A high-power, frequency-adjustable gyrotron loading test system for nuclear fusion

Abstract

This invention discloses a high-power, frequency-tunable gyrotron loading test system for nuclear fusion, relating to the field of nuclear fusion technology. It includes a 2-megawatt, 170 / 240 GHz frequency-tunable coaxial gyrotron and a loading test platform. The loading test platform comprises a gyrotron component loading system, a strong magnet system, a vacuum system, a power supply system, a load system, a cooling system, a monitoring and diagnostic system, and a control system. The component loading system is used for precise assembly; the strong magnet system provides an adjustable strong magnetic field; the vacuum system maintains an ultra-high vacuum; the power supply system includes a cathode power supply and a bulk power supply, with the bulk power supply acting as a high-voltage amplifier to achieve 10 kHz rapid power modulation; the cooling system provides independent active cooling; the load system simulates a real load; the monitoring and diagnostic system performs comprehensive testing; and the control system achieves coordinated control and rapid protection. This invention provides a complete solution for the development, testing, operation, and maintenance of a 2-megawatt, frequency-tunable gyrotron.

Description

Technical Field

[0001] This invention relates to the field of nuclear fusion engineering and high-power microwave vacuum tube technology, specifically to a high-power, frequency-tunable gyrotron loading test system for nuclear fusion. Background Technology

[0002] Magnetic confinement fusion is one of the most promising technological approaches to addressing future clean energy needs. In this field, electron cyclotron resonant heating (ECRH) and current-driven systems are the core means of maintaining and controlling high-temperature plasma. As the core high-power millimeter-wave source of the ECRH system, the performance of the cyclotron tube directly determines the efficiency, reliability, and real-time control capability of the entire heating system.

[0003] With the development of next-generation devices such as the International Thermonuclear Experimental Reactor (ITER) and the China Experimental Fusion Reactor (CFETR), plasma volumes are larger, magnetic fields are stronger, and the requirements for heating and current drive are more precise. This necessitates the development of gyrotrons used in the ECRH system towards megawatt-level single-tube output power, long pulse / continuous wave operation, higher operating frequencies (such as 170 GHz, 240 GHz, and even higher), and the ability to rapidly tune frequencies, in order to achieve higher energy deposition efficiency, suppress plasma instabilities, and adapt to the needs of different physics experiments.

[0004] However, existing gyrotron technology and its supporting research and testing systems face a series of severe technical bottlenecks and system-level challenges in meeting the aforementioned comprehensive requirements:

[0005] 1. Single-tube power and frequency increases face physical and engineering limits: Existing commercial megawatt-class gyroscopes are mostly designed with an output power of around 1MW and a fixed operating frequency. Further increasing the single-tube power to the 2MW level while simultaneously raising the operating frequency would drastically increase the power density and heat load within the tube. This leads to difficulties in heat dissipation in traditional resonant cavity structures, intensified mode competition, the risk of power breakdown in the output window, and difficulty in maintaining electron beam quality and stability. Although a few institutions internationally have achieved 1MW, hundred-second-level operation, higher power (e.g., 1.5MW and above) and higher frequency (e.g., above 200GHz) gyroscopes are still under development and have not yet become mature and reliable engineering products. In China, high-power gyroscopes (>500kW) suitable for fusion devices still mainly rely on imports.

[0006] 2. Low thermal management and energy recovery efficiency during long-pulse / continuous-wave operation: Under long-term operation, waste heat continuously accumulates in key components such as the collector and resonant cavity. Traditional cooling solutions struggle to achieve efficient and uniform heat dissipation, easily causing thermal deformation of components and disrupting the synchronization between the electromagnetic field and the electron beam. Simultaneously, the energy recovery efficiency of existing collectors is generally low, with a large amount of residual electron beam energy being converted into waste heat. This not only limits the overall tube efficiency (typically below 50%) but also places extreme pressure on the thermal management system.

[0007] 3. High system complexity, large footprint, and lack of a full-condition integrated verification platform: Due to the power limitation of a single gyroscope, existing large-scale fusion devices have to use dozens of gyroscopes operating in parallel to meet the total power requirements, resulting in a complex ECRH system structure and a huge footprint. More importantly, the development of gyroscopes spans multiple disciplines, including vacuum electronics, strong magnetic field technology, high-voltage engineering, and precision thermal management, making technology integration extremely difficult. Currently, the industry lacks a fully functional integrated loading test system capable of simulating the real operating environment of future fusion reactors. This makes it difficult to conduct full-condition performance testing, reliability assessment, and rapid iterative optimization at the system level for the development of new gyroscopes and their core components (such as new electron guns, coaxial inserts, and high-efficiency collectors), prolonging the transformation cycle from prototype to highly reliable engineering products and increasing development risks and costs.

[0008] Therefore, the industry urgently needs an innovative and systematic solution that can not only overcome the key technical challenges of high-power, high-frequency, and long-pulse operation from the perspective of physical design and core components, but also provide a fully integrated loading test platform to support the development, testing, and reliability verification of such high-end gyrotrons, thereby accelerating the fulfillment of the urgent need for high-performance electron gyro heating systems in next-generation nuclear fusion devices. Summary of the Invention

[0009] To address the problems existing in the prior art, this invention aims to provide an integrated gyrotron loading test system. It combines an optimized 2-megawatt, 170 / 240GHz frequency-adjustable gyrotron with a fully functional test platform to overcome key technical bottlenecks such as high-power high-frequency operation, long-pulse thermal management, and rapid control, and supports its full-condition testing and iterative development.

[0010] The technical solution adopted in this invention is as follows: A high-power, frequency-tunable gyrotron loading test system for nuclear fusion, comprising:

[0011] The gyrotron, which is a coaxial gyrotron, includes an electron gun, a coaxial insert, a beam channel, a resonant cavity, a transmitter, a quasi-optical transmission system, a mirror box and an output window, and a collector. The output power is in the 2 MW range, the center frequency is 170 GHz or 240 GHz and the frequency is adjustable, and it supports a long pulse operation mode with a pulse width of not less than 1 second and a continuous wave operation mode.

[0012] The loading test platform is connected to the gyrotube to form an integrated test system, which is used to support the full life cycle test verification of the gyrotube from joint investigation and manufacturing, factory testing to access nuclear fusion test and operation and maintenance;

[0013] The loading test platform is configured to adaptably provide corresponding power supply, cooling, magnetic field and load conditions according to the testing requirements of different models of gyrotubes. It includes a gyrotube component loading system, a strong magnet system, a vacuum system, a power supply system, a load system, a cooling system, a monitoring and diagnostic system and a control system.

[0014] The gyrotube component loading system is used to precisely coaxially align modular gyrotube components and assemble them into a complete gyrotube machine.

[0015] The strong magnet system is used to provide the gyrotube with a strong magnetic field that meets the resonant frequency and power requirements;

[0016] The vacuum system uses a sputtering ion pump and a non-evaporative getter to maintain the gyrotube at a pressure better than 10. -8 The ultra-high vacuum operating state of mbar is used to prevent gas ionization, high voltage breakdown and cathode poisoning.

[0017] The power system is used to provide electrical energy to the gyrotube test specimens with different power levels and modulation requirements, as well as the loading test platform itself.

[0018] The load system includes a dummy load for testing and a real load connected to the nuclear fusion device, used to simulate or bear the working load of the gyrotron in an actual nuclear fusion device.

[0019] The cooling system is used to provide independent active cooling for the resonant cavity, quasi-optical transmission system, collector and load system of the gyro, as well as the power system and the strong magnet system of the gyro.

[0020] The monitoring and diagnostic system is used to monitor and diagnose the operating conditions and parameters of the gyrotube and its components;

[0021] The control system is used for coordinated control, status monitoring, safety interlocking, and fault protection of the loading test platform.

[0022] Furthermore, the gyrotron component loading system includes: a modular component alignment and assembly fixture for achieving precise coaxial positioning and fixation of the electron gun, coaxial insert, beam channel, resonant cavity, quasi-optical transmission system, and collector; and an integrated test interface unit, which integrates standardized electrical, fluid, and signal interfaces for interfacing with the power system, cooling system, load system, control system, and monitoring and diagnostic system, for conducting joint debugging and loading tests on the assembled gyrotron.

[0023] Furthermore, the strong magnet system is a liquid helium-free superconducting magnet system with a magnetic field strength of 6.7-10.5 Tesla; the superconducting magnet system is also equipped with a multi-pole correction coil system for providing precise alignment for the coaxial insert.

[0024] Furthermore, the electron gun includes a reverse magnetron injection gun mounted at the bottom and a magnetron injection gun at the top. The anode and cathode profiles of the magnetron injection gun are configured to suppress electron beam corona and secondary electron generation. The magnetron injection gun emitter adopts an emission ring structure to reduce the impact of manufacturing and alignment tolerances of the emitter and its adjacent components on the performance of the gyrotron. The edge of the emission ring is coated with an anti-emission material. The heat-sensitive components in the electron gun are equipped with a direct cooling structure.

[0025] The coaxial insert is installed at the lower center of the gyrotube, and its position is adjusted relative to the cavity wall of the resonant cavity by a two-dimensional micro-drive device so that the concentricity of the coaxial insert and the resonant cavity meets the design requirements.

[0026] Furthermore, the resonant cavity includes an input conical section, a cylindrical interaction region, and an output conical section; the outer wall of the resonant cavity is provided with mode conversion ripples, and the cooling of the resonant cavity is achieved by filling the space between its outer wall and the external water cooling jacket with a Raschig ring or a microchannel cooling structure;

[0027] The cooling system includes an external water-cooled jacket surrounding the resonant cavity; the external water-cooled jacket is connected by an axial drive mechanism, enabling it to move along the axial direction of the resonant cavity to accommodate the differences in temperature and thermal expansion coefficient of different components during operation.

[0028] Furthermore, the collector is a multi-stage step-down collector based on the E×B drift concept; the multi-stage step-down collector includes multiple collection stages separated by conical spiral grooves, the spiral grooves being used to generate the angular component of the electric field to cooperate with the axial magnetic field to achieve E×B drift of the electron beam.

[0029] Furthermore, the output window is a chemical vapor deposition diamond Brewster angle window with a diameter of not less than 180 mm and a thickness of not less than 2 mm, and is installed at a Brewster angle.

[0030] Furthermore, the power supply system includes: a cathode power supply and a bulk power supply for providing accelerating voltage; a DC magnetic field power supply for providing the strong magnet system with the DC magnetic field required to generate a magnetic field of 6.7-10.5 Tesla; and an auxiliary power supply for powering the control system, cooling system, and other auxiliary equipment.

[0031] The negative terminal of the cathode power supply is connected to the cathode of the gyrotube, and the positive terminal is connected to the collector and grounded. The power supply establishes a main accelerating negative high voltage of -55kV to -85kV between the cathode and the collector, with a current of 45-100 amperes. It is controlled by a thyristor and is the main source of electron injection kinetic energy.

[0032] The negative terminal of the body power supply is grounded, and the positive terminal is connected to the body electrode. A positive voltage of +25kV to +35kV is provided between the collector and the body electrode. The body power supply is configured as a high-voltage amplifier with a bandwidth of not less than 10 kHz and an output voltage swing of not less than 15 kV. It is used to modulate the radio frequency output power of the gyrotron at a frequency of 10 kHz by adjusting its output voltage.

[0033] The sum of the absolute values ​​of the cathode power supply voltage and the body power supply voltage together constitutes the accelerating voltage of the gyrotron; the total accelerating voltage can be finely adjusted by independently adjusting the body power supply voltage; low modulation amplitude can be achieved by controlling only the body power supply voltage, while large amplitude power modulation requires synchronous modulation of the cathode power supply and body power supply voltages to prevent collector overload.

[0034] During wide-range power modulation, the control system synchronously adjusts the output voltage of the cathode power supply and the body power supply. While realizing rapid changes in the radio frequency power of the gyrotron, it ensures the stability of the collector potential and prevents it from overloaded due to sudden current changes.

[0035] The cathode power supply adopts pulse step modulation technology and is composed of multiple modular switching power supply units based on solid-state transformers connected in series. Its total capacity is more than twice the rated power of the gyrotron, and the output voltage stability is better than 0.1%. The solid-state transformer uses a wide bandgap power semiconductor switch for its isolated DC / DC converter, and the operating frequency is increased to the kilohertz or even megahertz level. It uses an intermediate frequency transformer to replace the traditional power frequency transformer to achieve electrical isolation.

[0036] Furthermore, the cooling system is a megawatt-level active cooling system, including a water cooling system, a liquid helium-free cooling system, and an oil cooling system, wherein: the liquid helium-free cooling system is used to provide cooling for the liquid helium-free superconducting magnet system; the oil cooling system is used to provide cooling for the power supply system and parts of the electron gun that are not suitable for water cooling;

[0037] The cooling system employs dual power supply and includes multiple independent sub-cooling circuits to independently cool and monitor the heat load of the electron gun, coaxial insert, beam channel, resonant cavity, quasi-optical transmission system mirror, mirror box, output window, and collector of the gyrotron. Each branch is equipped with flow, temperature, and pressure sensors.

[0038] Furthermore, the monitoring and diagnostic system includes:

[0039] A power measurement unit is used to measure the output power of the gyrotron by calorimetry and to monitor the instantaneous radio frequency power through a directional coupler and a detector.

[0040] A frequency measurement unit for measuring radio frequency via a spectrum analyzer connected to a directional coupler;

[0041] The mode purity analysis unit is used to acquire the amplitude and phase distribution of the radio frequency beam through non-contact measurement technology, and to evaluate the purity of the output mode accordingly.

[0042] Furthermore, the control system includes:

[0043] The host computer and human-computer interaction software are used to select the working mode and set the operating parameters through a local or remote computer.

[0044] The logic controller is used to process information from external devices, power supply status, cooling system status, and vacuum system status, and to implement logical blocking of various control signals and commands.

[0045] The pulse controller, based on a field-programmable gate array, is used to perform precise timing control on and off of multiple pulse step modulation modules in the power supply system. The control interval is adjustable in the range of 1μs to 1s.

[0046] The interface circuit is used to convert the switching control signal and fault protection signal of the pulse controller into optical signals and transmit them through optical fiber to achieve high-voltage isolation between the controller and the high-voltage equipment.

[0047] The control system is configured to have rapid fault detection and execution capabilities, capable of judging system faults, including short circuits, within less than 20 microseconds and triggering protection actions. The protection actions include triggering a fast protection switch disconnection circuit connected in series in the high-voltage circuit. The fast protection switch is a water-cooled IGBT switch with a rated voltage of not less than 100 kV DC and a rated current of not less than 100 Amperes. The total time from fault detection to main circuit disconnection is within a few microseconds, so that the energy deposition at the fault point is less than 10 Joules.

[0048] The control system is also used to generate control signals to drive the bulk power supply to work as a high-voltage amplifier, so as to achieve modulation of the millimeter-wave output power of the gyrotube at a frequency of not less than 1kHz.

[0049] The logic controller is based on a programmable logic controller and monitors the temperature, pressure and flow parameters of the cooling system through a remote expansion module. It is also used to realize system start-up and shutdown sequences, interlocking of cooling and vacuum systems, fault signal latching, and blocking of power operation commands.

[0050] The control system also integrates at least three fault protection mechanisms, including output overvoltage protection, dual output overcurrent protection, rotary tube fault protection, crowbar action protection, and manual emergency stop protection.

[0051] The beneficial effects of this invention are as follows:

[0052] (1) This invention provides a systematic solution with clear technical indicators and specific technical paths. Its comprehensive performance directly addresses and meets the forward-looking requirements of the next-generation nuclear fusion device for the electron cyclotron heating system. Compared with the existing commercially available 1 MW single-frequency cyclotron technology, the design of this invention increases the single tube output power to the 2 MW level, sets the center operating frequency at 170 GHz or 240 GHz with adjustable capability, and systematically supports long pulse and continuous wave operation modes. To achieve this comprehensive performance leap, this invention proposes a series of interrelated and synergistic specific technical features, including but not limited to: a specific configuration electron gun for generating and confining high-quality electron beams, a 10.5 Tesla-level superconducting magnet for providing a strong magnetic field for high-frequency operation, a 180 mm diameter chemical vapor deposition diamond window to ensure high-power millimeter-wave output, a coaxial insert and matching alignment mechanism to achieve mode stability and efficiency improvement, and a multi-stage step-down collector based on the E×B drift principle to improve the overall tube efficiency to over 60%. The combination of these technical features constitutes a complete and feasible technical solution that directly addresses the technical requirements of next-generation nuclear fusion devices for high-power, high-frequency, and high-reliability electron cyclotron heating sources.

[0053] (2) This invention designs the gyrotube body and the fully functional loading test platform as an organic whole, thereby realizing a closed loop of performance verification and iterative optimization at the system level. Specifically: To address extreme thermal management challenges, an independent active cooling circuit and a mobile external water-cooling jacket structure adaptable to thermal expansion are designed for each heat-generating component (coaxial insert, resonant cavity, collector, and output window); to meet the requirements of fast and accurate power control, a bulk power supply architecture with high-voltage amplifier characteristics (bandwidth ≥ 10kHz, swing ≥ 15kV) is developed and works in conjunction with the main power supply based on pulse step modulation technology; to ensure system safety and reliability, a hierarchical control and protection system including microsecond-level fast protection switches and multiple hardware interlocks is constructed. This system-level integrated innovation ensures the reliable generation and effective control of 2 MW-level power at higher frequencies.

[0054] (3) The loading test platform of the present invention is not only for verifying specific models of gyrotrons, but also for providing a standardized and universal R&D infrastructure. The platform supports rapid replacement and accurate testing of key components (such as various electron guns and collectors) of different design configurations through modular component alignment and assembly tooling and integrated test interface units; its power supply, cooling, load and diagnostic systems have sufficient capacity margin and interface flexibility to adapt to gyrotrons of different power levels and frequency ranges. This allows the entire process from core component development and whole-machine integration and debugging to factory reliability assessment to be completed within the same platform system, providing a physical basis for rapid iteration of "design-test-optimization" and significantly reducing the R&D threshold and cycle.

[0055] (4) This invention clearly proposes a series of specific technical parameters and performance indicators such as output power, operating frequency, magnet field strength, diamond window size, cooling system capacity, power modulation bandwidth, and protection response time. For example, CVD diamond windows with a thickness of not less than 2.0 mm, spiral groove collector structures for achieving energy recovery efficiency of more than 77%, and microsecond-level protection switches to ensure energy deposition of less than 10 joules provide clear design inputs and verification standards for those skilled in the art, enabling the system described in this invention to have a clear path from scheme to engineering implementation. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0057] Figure 2 This is a schematic diagram of the 2-megawatt coaxial gyroscope structure of the present invention.

[0058] Figure 3 This is a schematic diagram of the initial velocity and trajectory of electrons emitted by the gyrotube of the present invention.

[0059] Figure 4 This is a schematic diagram of the electron gun emission ring structure of the present invention.

[0060] Figure 5 This is a diagram of the operating modes of the non-coaxial gyrotron, which is highly competitive in the 140 GHz mode.

[0061] Figure 6 This is a schematic diagram of the dimensions of a coaxial resonant cavity.

[0062] Figure 7 This is a diagram showing the operating mode selection for a 170GHz coaxial gyrotron.

[0063] Figure 8 This is a schematic diagram of the coaxial insert structure of the present invention.

[0064] Figure 9 This is a schematic diagram of the multi-pole correction coil of the strong magnet system of the present invention.

[0065] Figure 10 This is a schematic diagram of the high-efficiency Raschig ring cooling structure of the present invention; wherein, Figure 10 (a) is an overall view of the cavity, the external water jacket, and the Raschig ring; Figure 10 (b) is an enlarged view of the Raschig ring structure.

[0066] Figure 11 This is a cross-sectional schematic diagram of the resonant cavity cooling structure of the present invention.

[0067] Figure 12 This is a schematic diagram of the structure of the chemical vapor deposition diamond window of the present invention.

[0068] Figure 13 This is a schematic diagram of a multi-stage step-down collector; in which, Figure 13 (a) is the design principle diagram of E×B drift; Figure 13 (b) is a schematic diagram of a multi-stage step-down collector with a spiral electrode.

[0069] Figure 14 This is a schematic diagram of the gyrotron power supply configuration of the present invention.

[0070] Figure 15 This is a schematic diagram of the accelerating voltage and electron current of the gyrotron in this invention.

[0071] Figure 16 This is a schematic diagram of the main circuit structure of the high-voltage power supply system of the present invention.

[0072] Figure 17 This is the three-stage circuit topology diagram of the solid-state transformer of this invention.

[0073] Figure 18 This is a schematic diagram of the active cooling system allocation and monitoring of the present invention.

[0074] Figure 19 This is a schematic diagram of the millimeter-wave transmission and load link of the present invention.

[0075] Figure 20 This is a schematic diagram of the radio frequency conditioning unit structure of the present invention.

[0076] Figure 21 This is a schematic diagram of the power control system structure of the present invention.

[0077] In the diagram: 1: Gyroscope; 11: Electron gun; 111: Radiation shielding material; 112: Magnetron injection gun; 113: Inverse magnetron injection gun; 12: Coaxial insert; 13: Beam channel; 14: Resonant cavity; 15: Emitter; 16: Quasi-optical transmission system; 17: Lens box; 171: Water-cooled ceramic tube; 18: Output window; 19: Collector;

[0078] 2: Gyroscope component loading system; 3: Strong magnet system; 31: Multi-pole correction coil; 4: Vacuum pumping system; 5: Power supply system; 6: Load system; 61: Dummy load; 62: Real load; 7: Cooling system; 71: Water cooling system; 72: Liquid helium-free cooling system; 73: Oil cooling system; 8: Monitoring and diagnostic system; 9: Control system;

[0079] F: Filament; K: Cathode; A: Anode; B: Body electrode; C: Collector electrode; FPS: Filament power supply; MPS: Cathode power supply; BPS: Body power supply; APS: Anode power supply;

[0080] J1: Plane mirror; J2, J5: Secondary reflecting mirrors; J3, J4: Grating polarizers. Detailed Implementation

[0081] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0082] The electron cyclotron system in nuclear fusion is responsible for key functions including initiating, maintaining, and assisting tokamak plasma discharge. All the physical requirements of existing high power density (HCD) systems can be met by electron cyclotron systems, requiring two or three injection frequencies and up to six equatorial ports to accomplish all tasks. Not only is high power required, but the power deposition region must cover the entire plasma radius from the center to the edge, a goal currently impossible to achieve with a single injection frequency. A sufficient number of high-power cyclotron tubes are needed to provide the required power to the system. For a current emitter design with 22 beamlines and two clusters per port, an electron cyclotron heating system is required to provide 30 MW for boundary heating, 30 MW for unstable low-order modes, and 70 MW for thermionic stabilization, totaling 130 MW.

[0083] The International Thermonuclear Experimental Reactor (ITER) requires 24 gyrotrons operating at 170 GHz, with an output power of 1 MW, capable of continuous operation for 3600 seconds. Future gyrotrons for nuclear fusion require significant advancements, increasing output power from 1 MW to 2 MW, operating at multiple frequencies for versatility, and reaching operating frequencies above 200 GHz. Gyrotron power, efficiency, and frequency are key issues for future nuclear fusion electron gyro heating systems. Operation at different frequencies and rapid frequency adjustability with tuning steps of 2 to 3 GHz are required. High levels of reliability, availability, maintainability, and detectability (RAMI level) and advanced gyrotron control are also essential.

[0084] Please see Figure 1 The high-power, frequency-adjustable gyrotron loading test system for nuclear fusion provided by this invention is based on the integration of a high-performance gyrotron body and a fully functional loading test platform, forming an organically unified whole. The system includes a gyrotron 1 and a loading test platform, wherein the loading test platform includes a gyrotron component loading system 2, a strong magnet system 3, a vacuum system 4, a power supply system 5, a load system 6, a cooling system 7, a monitoring and diagnostic system 8, and a control system 9.

[0085] The gyrotron provided in this embodiment has a coaxial cavity structure, designed with an output power of 2 megawatts, a center operating frequency of 170 GHz or 240 GHz, and a certain range of frequency adjustability to support long pulse (≥1 second) and continuous wave (CW) operation. Figure 2 As shown, the coaxial gyrotron of this embodiment is mainly composed of modular components such as an electron gun 11, a coaxial insert 12, a beam channel 13, a resonant cavity 14, a transmitter 15, a quasi-optical transmission system 16, a mirror box 17, an output window 18, and a collector 19.

[0086] The connection relationship of the above components is as follows: the electron gun 11 is installed at the bottom of the gyrotube 1, and the annular electron beam emitted by its cathode moves upward under the guidance of a strong magnetic field; the coaxial insert 12 is coaxially installed at the center of the gyrotube 1 and extends axially into the resonant cavity 14; the beam channel 13 is the electron beam transmission path connecting the electron gun 11 and the resonant cavity 14. The annular electron beam generated by the electron gun 11 is adiabatically compressed through the beam channel 13 under the guidance of a strong magnetic field, gradually increasing the energy density and transverse velocity component of the electron beam, and finally injecting it into the resonant cavity 14 at an optimized velocity ratio; the resonant cavity... Located above the electron gun 11, the 14 unit, together with the coaxial insert 12, forms the beam-wave interaction region. The transmitter 15 "unfolds" the high-order cylindrical waveguide mode within the resonant cavity 14 and radiates it into free space, forming a divergent beam with a specific amplitude and phase distribution. The mirror box 17 is a vacuum-sealed cavity, which is vacuum-sealed with the resonant cavity 14, the output window 18, and the collector 19. Its inner wall is lined with an internal load consisting of water-cooled ceramic tubes 171, used to absorb stray radiation generated during the quasi-optical transformation (typically up to 8% of the output power). All quasi-optical components are installed inside the mirror box 17. The divergent beam is reflected, focused, and phase-corrected by a series of parabolic mirrors, ellipsoidal mirrors, and plane mirrors, and is finally converted into a quasi-Gaussian beam with concentrated energy and a defined propagation direction. The quasi-Gaussian beam, after being transformed by the quasi-optical transmission system 16, is radiated out of the vacuum chamber through the output window 18 with optimized mode purity, beam waist radius, and propagation direction. The output window 18 employs a chemical vapor deposition diamond Brewster angle window, mounted at a 67.2° angle on the side wall of the mirror box 17 to achieve millimeter-wave output. The depleted electron beam, after interaction, continues to move upwards under the guidance of the residual magnetic field, entering the collector 19 located at the top of the gyrotube. These components are arranged sequentially along the gyrotube axis and are all encapsulated within a vacuum housing, forming a complete gyrotube system. Each component is rapidly connected to the power system 5, cooling system 7, and control system 9 of the loading test platform via an integrated test interface unit, forming an integrated test system.

[0087] To achieve a 2-megawatt output power, a 170GHz or 240GHz center frequency, and adjustable frequency capability, this invention utilizes the following collaborative technical means:

[0088] (1) A 6.7-10.5 Tesla-level superconducting magnet system is used to provide the required strong magnetic field conditions for the 170GHz or 240GHz working frequency based on the proportional relationship between electron cyclotron frequency and magnetic field strength.

[0089] (2) The resonant cavity 14 adopts a high-order operating mode design. The cavity radius corresponding to this high-order operating mode is increased, which limits the peak value of the wall ohmic load to the design target range of 2 kilowatts per square centimeter, so that the gyrotube can withstand 2 megawatts of power operation without cavity thermal breakdown.

[0090] (3) The coaxial insert 12 is introduced to change the boundary conditions of the resonant cavity 14, effectively widening the frequency interval between different modes, enhancing mode selectivity, enabling the required higher-order mode to oscillate stably while suppressing competing modes; by adjusting the axial position of the coaxial insert 12, the resonant frequency can be continuously adjusted within a certain range to achieve electronic tuning.

[0091] (4) The output window 18 adopts a CVD diamond Brewster corner window with a diameter of not less than 180 mm and a thickness of not less than 2 mm. Its low dielectric loss and high thermal conductivity characteristics enable it to withstand 2MW millimeter wave power output without thermal cracking.

[0092] (5) The electron gun 11 adopts a magnetron injection gun design, which can provide the large current electron beam (tens of amperes) required for 2MW level power, while maintaining low velocity dispersion and high-level flow characteristics to ensure beam interaction efficiency;

[0093] (6) Collector 19 adopts a multi-stage pressure reduction collector. The multi-stage pressure reduction collector is designed based on the E×B drift principle. The energy recovery efficiency can reach more than 77%, which can improve the overall tube efficiency to more than 60% and effectively reduce the heat load pressure.

[0094] The above-mentioned technical means work together to form a complete technical solution for realizing a 2MW-level, 170 / 240GHz frequency adjustable gyrotron.

[0095] The high-power, frequency-tunable gyrotron technology provided by this invention can be summarized as follows: It employs a coaxial insert, and the larger cavity size of the coaxial gyrotron allows for stable operation in high-performance modes. Selecting higher-order operating modes and increasing the cavity radius controls the peak ohmic load at a reasonable level (2 kW per square centimeter). The coaxial gyrotron can meet the requirements of 2 MW output power and frequency tunability. It changes the physical structure of conventional gyrotron resonant cavities, representing an advanced form developed by overcoming the inherent defects of conventional cylindrical gyrotrons such as mode competition and power bottlenecks. In addition to using a coaxial gyrotron insert, it addresses the power output bottleneck with a CVD diamond output window, generates high-quality electron beams with an advanced magnetron injection gun and superconducting magnets, improves interaction efficiency with a non-uniform resonant cavity and optimized electron dynamics, and utilizes multi-stage step-down collectors for energy recovery and heat load management. Coupled with precise quasi-optical conversion and a powerful active cooling structure and system, it ultimately achieves stable operation of a 2 MW-class, continuous-wave, high-efficiency, frequency-tunable gyrotron.

[0096] Electron Gun 11:

[0097] The power of a gyrotron is proportional to the voltage and current of the electron beam. Increasing the power requires improving the electron gun's ability to withstand higher voltages (above 100kV) and larger currents. Gyrotron efficiency is the ratio of output microwave power to input electron beam power; improving efficiency means reducing heat energy consumption at the source. This involves increasing the electron gun voltage and current to increase power while precisely controlling the ratio of the electron beam's lateral velocity to its axial velocity (see...). Figure 3 The electron velocity v is the sum of the axial velocity v1 and the lateral velocity v2. e This invention optimizes the electron beam quality to achieve optimal "phase focusing" within the resonant cavity. Simultaneously, it optimizes the magnetic field profile from the electron gun to the resonant cavity, achieving adiabatic compression of the electron beam, increasing its energy density and coupling efficiency with the microwave mode, and reducing parasitic oscillations in the electron beam compression region. The invention uses a magnetron injection gun composed of a single cathode or multiple emitting surfaces to optimize the electron beam quality, resulting in low velocity dispersion and high laminar flow characteristics, enabling more efficient coupling with the microwave mode. It also improves the performance of the electron gun and electron optics system, minimizing the impact of manufacturing tolerances and misalignments in the magnetron injection gun and coaxial inserts on the quality of the generated electron beam.

[0098] See Figure 8 The electron gun 11 of this invention includes a reverse magnetron injection gun 113 mounted at the bottom and a magnetron injection gun 112 at the top. The anode and cathode profiles of the magnetron injection gun 112 are co-optimized. By modifying the anode and cathode profiles, the "electron beam corona" phenomenon caused by magnetically trapped electrons between the cathode and the interaction resonant cavity is suppressed, and the possibility of secondary electrons being generated in the non-emission area of ​​the electrodes due to bombardment by trapped particles is minimized. Figure 4 As shown, the electron gun employs a ring-shaped emitter with its edges coated with an anti-emission material 111 to reduce the impact of manufacturing and assembly tolerances on beam quality. To cope with the heat load caused by long-pulse operation, a direct cooling channel is integrated inside high-heat-load components (such as the cathode support structure) near the emitter. Forced liquid cooling improves temperature distribution, suppresses thermal expansion, and thus maintains the stability of electron beam parameters.

[0099] Coaxial insert 12:

[0100] Coaxial cavity designs are better suited to meet the requirements of 2 MW output power and ≥170 GHz frequency compared to traditional cavity designs. Traditional cavity designs currently cannot achieve these performance targets. Further research is needed on TE... 34，11The effects of structural parameters, electron beam parameters, and cavity wall loss of a coaxial cavity gyroscope on beam-beam interaction were investigated. It was found that coaxial cavity gyroscopes have advantages such as alleviating mode competition, improving the stability of single-mode operation, and increasing power capacity. The most direct way to increase the power capacity of a gyroscope is to select higher-order modes as the operating modes. However, higher-order modes bring severe mode competition, reducing beam-beam interaction efficiency. The operating mode diagram of a 140 GHz non-coaxial gyroscope is shown below. Figure 5 As shown, TE 28,8 Models also have dense pattern maps, and the competition among models is actually very fierce.

[0101] Using coaxial inserts and coaxial cavity structures is an effective method to suppress competing modes. The principle of mode selection is: the operating mode spectrum should be relatively sparse to reduce modes that may compete; the energy of the transverse electric field of the operating mode should be concentrated in the middle position of the conductors inside and outside the resonant cavity to enhance wave-beam interaction and reduce ohmic losses at the cavity walls.

[0102] The enhancement mode selectivity of the coaxial cavity allows for stable operation in very high operating modes, which is compatible with the larger cavity size. Selecting higher-order operating modes and increasing the cavity radius can keep the peak ohmic load of the cavity at a reasonable level (2 kW per square centimeter). The coaxial gyrotron changes the physical structure of the conventional gyrotron resonator cavity and is an advanced form developed by overcoming the inherent defects of conventional cylindrical gyrotrons such as mode competition and power bottlenecks.

[0103] TE m，n The cutoff frequency of the operating mode can be approximately determined by the inner radius of the outer waveguide of the resonant cavity. and eigenvalues Find:

[0104] Formula I,

[0105] Where c is the speed of light.

[0106] Figure 6 The dimensions of the coaxial resonant cavity are shown in Table 1, and the corresponding parameter values ​​are shown in Table 1.

[0107] Table 1:

[0108]

[0109] When the outer radius and operating frequency are preset to 22 mm and 170 GHz, the characteristic value can be obtained from Equation I. =78.33. Analyze the patterns with eigenvalues ​​around 78.33, and select a suitable pattern as the working mode.

[0110] When designing the inner conductor radius and electron beam guiding radius, the caustic radius... This is a very important parameter. Caustic radius It is an approximate inner boundary of the transverse electric field:

[0111] Formula II,

[0112] in, These are the order parameters of the corresponding waveguide modes, and TE. m,n The meaning of 'm' in the pattern is consistent; It is TE m,n The feature value corresponding to the pattern.

[0113] The maximum radius of the inner conductor should be smaller than the caustic radius of the operating mode, and the optimal radius of the electron beam guiding center should be equal to the radius at the point of maximum transverse field strength of the operating mode, and slightly larger than the caustic radius of the operating mode. In this way, the transverse field distribution of the operating mode is almost unaffected by the inner conductor, the operating mode can interact efficiently with the electron beam, and it is beneficial for suppressing competing modes.

[0114] Based on the principle of mode selection that the energy of the transverse electric field should be concentrated at the midpoint between the inner and outer conductors of the resonant cavity, and the physical meaning of the caustic radius, and The ratio was set in the range of 0.4 to 0.5. Figure 7 The operating mode selection spectrum of the 170 GHz coaxial gyrotron shows modes with eigenvalues ​​ranging from 77.5 to 79.5 and their beam coupling coefficients (electron beam guide center radius). (10.1mm). From Figure 7 The pattern can be seen from it There are fewer competing patterns nearby, and the radius of the electronic injection guidance center is smaller. When the diameter is 10.1 mm, the same direction rotating mold The coupling coefficient with the electron beam is the largest, and it can be calculated to obtain... The above conditions are met. Therefore, the same-direction rotating mold is selected. As a work mode ( Figure 7 The red lines represent the same-direction rotating molds, and the blue lines represent the opposite-direction rotating molds.

[0115] After selecting the operating mode, the effects of current, magnetic field strength, and cavity wall ohmic loss on beam-wave interaction were analyzed, and the operating parameters were optimized. Simulation results show that: when the magnetic field strength remains constant, the operating frequency increases slowly with increasing operating current, and the interaction efficiency first increases and then decreases; the guiding magnetic field strength has a significant impact on beam-wave interaction efficiency; as the magnetic field increases, the maximum interaction efficiency under each magnetic field will decrease; cavity wall loss reduces both interaction efficiency and operating frequency; the peak ohmic loss density on the inner and outer conductor surfaces increases with increasing current; when velocity dispersion is no greater than 10%, velocity dispersion has a relatively small impact on interaction; when the electron beam thickness is less than 0.44 mm, the changes in operating frequency and interaction efficiency are small. Through optimization of the simulated operating parameters, when the electron beam current is 68 A, the operating voltage is 65 kV, and the guiding magnetic field strength is 6.58 T, an output power of 2.18 MW and an efficiency of 49.23% can be obtained, with a peak ohmic loss density of 1.94 kW / cm² on the outer cavity wall. 2 The peak ohmic loss density on the surface of the inner conductor is less than 0.15 W / cm². 2 Coaxial gyrotrons can achieve 2-megawatt-level RF output power. For example... Figure 8 As shown, the coaxial insert 12 of this invention is a precision-machined metal cylinder (inner conductor), approximately 1.2 meters in length, coaxially mounted at the center of the gyrotube 1. The coaxial gyrotube has an inner conductor precisely inserted into a conventional cylindrical cavity, forming a structure similar to a coaxial cable. The inserted inner conductor alters the electromagnetic field distribution and boundary conditions of the cavity, effectively widening the frequency gap between different modes and achieving "mode purification." Only the required higher-order modes can oscillate stably, while the frequencies of other competing modes are effectively suppressed. The resonant frequency of the coaxial gyrotube is jointly determined by the gap between the inner and outer conductors. This structure is less sensitive to machining errors. By precisely moving the axial position of the inner conductor, the resonant frequency can be continuously and rapidly adjusted within a certain range, achieving electronic tuning.

[0116] The coaxial insert 12 lays the foundation for the feasibility of a 2-megawatt, frequency-adjustable coaxial gyrotube.

[0117] The concentricity of the coaxial insert 12 with the inner wall of the resonant cavity 14 is crucial to mode purity. The position of the coaxial insert 12 is adjusted relative to the cavity wall of the resonant cavity 14 using a two-dimensional micro-drive device to ensure that the concentricity of the coaxial insert with the resonant cavity meets design requirements. Any precision positioning mechanism capable of achieving two-dimensional micron-level displacement adjustment can be applied to this invention without departing from the scope of protection of this invention.

[0118] To achieve sub-millimeter alignment accuracy, such as Figure 9As shown, this embodiment integrates a 3×4 multipole correction coil system into the strong magnet system. The strong magnet system itself is a liquid helium-free superconducting magnet with a central magnetic field strength of 6.7-10.5 Tesla (T) and an aperture of 261 mm, capable of providing the required resonant magnetic field for cyclotron oscillations at 240 GHz. By independently controlling the current of the multipole correction coil 31, a small lateral electromagnetic force can be applied to the coaxial insert 12, achieving micron-level positioning adjustment in the two-dimensional direction, thereby compensating for machining and assembly errors.

[0119] Beam channel 13:

[0120] The beam channel 13 is the electron beam transmission path connecting the electron gun 11 and the resonant cavity 14. The annular electron beam generated by the electron gun 11 is adiabatically compressed through the beam channel 13 under the guidance of a strong magnetic field, gradually increasing the energy density and transverse velocity component of the electron beam, and finally injecting it into the resonant cavity 14 at an optimized speed ratio.

[0121] Resonant cavity 14:

[0122] The resonant cavity 14 is the region where energy exchange occurs between the electron beam and electromagnetic waves. Along with ohmic surface losses, the radio frequency power generated by the interaction of the electron waves is formed within the cavity. This invention optimizes the geometric profile of the resonant cavity, dividing its structure into a linear input cone segment, a cylindrical interaction region, and a linear output cone segment to improve mode purity and reduce electron beam velocity dispersion, thereby achieving TE... 34,19 The power conversion rate from one mode to another is less than 0.2%. Mode conversion ripples are etched on the outer wall of the resonant cavity to suppress unwanted competing modes. Higher-order electromagnetic modes are used to increase the cavity size, thereby enabling it to withstand higher power without breakdown, while keeping the peak ohmic load on the walls within acceptable limits for copper at room temperature (1 kW / cm²).

[0123] In a gyrotron, a significant amount of energy exchange occurs between the ring-shaped rotating electron beam and the millimeter wave. The waveguide behaves like a true open resonant cavity, requiring careful management of the thermal load. The heat dissipation capacity and thermomechanical stability of the resonant cavity largely determine the performance of the gyrotron. Effective cooling allows for the selection of modes with higher electron beam / wave interaction efficiency in higher-order operating modes, thereby achieving an overall increase in radio frequency (RF) output power. To manage peak wall loads up to 2 kW / cm², this invention employs an innovative design for resonant cavity cooling:

[0124] First, such as Figure 10 , Figure 11 As shown, between the outer wall of the resonant cavity 14 and the external water-cooling jacket ( Figure 11 The area indicated by medium gray is filled with copper Raschig rings to form a porous brazed structure with high thermal conductivity, achieving efficient heat transfer. See also Figure 10 (b) A Raschig ring is a small hollow cylinder (of the same length and height) made of copper and coated with a metallic alloy. Multiple Raschig rings are filled within a thin annular space outside the cavity where electromagnetic interactions occur, and are welded together by the coating to form a porous structure with high thermal conductivity. Raschig rings in cavity resonators can handle peak heat loads up to approximately 20 MW / m². Microchannels consist of a series of circular or semi-circular channels drilled around the cavity, utilizing the high-speed turbulence of the coolant to achieve a large heat transfer coefficient, overcoming the limitations of Raschig rings under low water flow conditions. The Raschig ring cooling system consists of a porous medium composed of a number of small hollow cylinders, forming a macaroni-like structure. These cylinders are made of copper and are in the millimeter range in size, length, and diameter. To create the porous medium, annular radiators coated with a thin layer of brazing alloy are injected into the area between the resonant cavity and the external water jacket and brazed in a furnace.

[0125] In addition, the external water-cooling jacket surrounding the resonant cavity is connected by an axial drive mechanism, allowing it to move along the axis of the resonant cavity. Before or during long pulse operation, the external water-cooling jacket can be moved to compensate for the dimensional changes in the resonant cavity caused by thermal expansion, ensuring optimal cooling clearance and avoiding excessive thermal stress.

[0126] Launcher 15:

[0127] The transmitter 15 "unfolds" the high-order cylindrical waveguide mode within the resonant cavity 14 and radiates it into free space, forming a divergent beam with a specific amplitude and phase distribution.

[0128] Quasi-optical transmission system 16:

[0129] The quasi-optical transmission system 16 consists of a series of mirrors (such as plane mirrors, gratings, and ellipsoidal mirrors) and is a key intermediate link connecting the resonant cavity 14 and the output window 18. Its core function is to transmit the higher-order operating modes (such as TE) generated by the resonant cavity 14. 34,19 The mode is efficiently and with low loss converted into a quasi-Gaussian beam suitable for free space transmission and subsequent mode purification, and guided to be incident on the output window 18 with the correct direction and polarization state.

[0130] Mirror Box 17:

[0131] All quasi-optical components are installed inside the mirror housing 17. During quasi-optical transformations, a small amount of stray radiation inevitably occurs that is not captured by the mirror or is caused by impure mode conversion. If this stray radiation directly bombards the inner wall of the mirror housing 17, it can cause localized overheating and may induce parasitic oscillations. Therefore, the inner wall of the mirror housing 17 is fitted with an internal load consisting of water-cooled ceramic tubes 171 (see [link to documentation]). Figure 2These internal loads have a large equivalent surface area and efficient cooling capacity, capable of absorbing leakage losses of up to about 8% of the gyrotube output power, effectively controlling stray radiation levels and heat load within the mirror box 17.

[0132] Output window 18:

[0133] The quasi-Gaussian beam, transformed by the quasi-optical transmission system 16, is radiated out of the vacuum chamber through the output window 18 with optimized mode purity, beam waist radius, and propagation direction, before entering the subsequent RF conditioning unit and load system. Diamond is a material with low dielectric constant, high thermal conductivity, and high strength. At ε = 5.67 and 300K, its thermal conductivity is 1900 W / mK, and its mechanical strength reaches 400 MPa, sufficient to diffuse the losses within the window to the outside of the diamond disk frame for cooling. Figure 12 As shown, this embodiment uses an elliptical diamond window, fabricated by chemical vapor deposition (CVD) with a diameter of 180 mm, a thickness of 2 mm, and low internal stress, as a high-efficiency output window. It is installed at a Brewster angle (approximately 67.2°) and connected to a window unit with a diameter of 63.5 mm and a transmission power of 2 MW. The window edge is connected to the copper window frame using a high-temperature active metal brazing process and is equipped with a separate water-cooling ring for effective cooling. The diamond window possesses high thermal conductivity, low microwave loss, and low internal stress. By improving the quality and welding of the diamond window, it can withstand enormous microwave power and the resulting heat. Multi-stage step-down collector:

[0134] The collector electrode is used to recover the residual energy of the electron beam after interaction and is key to improving overall tube efficiency. After giving up its energy, the electron beam still carries a large amount of kinetic energy, which bombards the collector electrode and generates enormous heat. By applying a decreasing potential to the step-down collector electrode, the electrons are slowed down before reaching the collector electrode surface, recovering some of their kinetic energy as electrical energy, while distributing the heat load over a larger area.

[0135] This implementation employs a multi-stage step-down collector based on the E×B drift principle. Its inner wall is divided into multiple collecting stages with progressively decreasing potentials by a conical spiral groove. The spiral groove structure generates an angular component of the electric field in the radial direction, which, together with the axial residual magnetic field, causes electrons to undergo E×B drift, guiding them to different collecting stages and achieving staged energy recovery. This design can increase the collector's own energy recovery efficiency to approximately 77%, thereby helping the overall tube efficiency exceed 60%.

[0136] The core task of the "multi-stage step-down collector," a key component of the gyrotron, is to recover the residual energy of "waste electrons" after microwave energy has been extracted from the electron beam. After microwaves are generated in the core cavity of the gyrotron, the "waste electron beam" still carries high velocity and kinetic energy. If it were to directly bombard a collector electrode at a high potential, this energy would be entirely wasted as heat. The multi-stage step-down collector achieves energy recovery by dividing the collector electrode into multiple electrodes with progressively decreasing potentials. As the waste electrons enter each stage, they are subjected to a reverse decelerating electric field. During this deceleration, their kinetic energy is recovered by the electric field and converted into electrical energy. This recovered electrical energy can be returned to the power system or used in other auxiliary circuits, thereby reducing the total power drawn from the grid. By recovering energy, the residual kinetic energy of the electrons when they finally bombard the collector electrode surface is greatly reduced, directly lowering the heat dissipation pressure on the collector electrode and improving reliability and lifespan.

[0137] With the increasing power of electron cyclotron resonant heating systems and the extension of pulse length to continuous waves, the efficient operation of cyclotrons has become increasingly important. Cyclotrons employing a single-stage step-down collector can achieve an overall efficiency of 50% to 55%. However, by employing a multi-stage step-down collector system based on the E×B drift concept, the magnetically confined electron beam of the cyclotron is efficiently distributed to different electrodes, further improving the overall efficiency of the cyclotron, with a collector efficiency as high as 91%. Figure 13 (a) illustrates the design principle of E×B drift. Figure 13 (b) shows a multi-stage step-down collector with helical electrodes.

[0138] The helical cut of the multi-stage step-down collector separates the two stages, generating an azimuth electric field that guides the radial drift of the electron center. This directs electrons of different energies to electrodes with different potentials, maximizing kinetic energy recovery. The unique advantages of the E×B type multi-stage magnetron collector also include its ability to handle secondary electrons and its high immunity to stray magnetic fields and electron beam deviation. Using an optimized two-stage design, the collector efficiency can reach 77%. Assuming an interaction efficiency of 35% and internal losses of 10% in the gyrotron, the overall gyrotron efficiency can reach 63%.

[0139] The loading test platform provides comprehensive support for the assembly, testing, and iteration of the gyrotron body, and mainly includes the following subsystems:

[0140] (1) Rotor component loading system 2

[0141] The gyrotube component loading system 2 is a fundamental component of the loading test platform. Its core function is to precisely assemble modular key gyrotube components into a complete gyrotube machine and provide physical conditions for subsequent component iteration, correction, and reloading.

[0142] To meet the stringent requirements for component coaxiality in a 2 MW, 170 / 240 GHz coaxial gyrotron, this invention provides a modular component alignment and assembly fixture. This fixture, using the optical axis of the gyrotron system as a reference, provides a precise mechanical positioning interface for fixing and guiding the following core components: electron gun 11, coaxial insert 12, beam channel 13, resonant cavity 14, quasi-optical transmission system 16, and collector 19.

[0143] To address the concentricity requirements between the coaxial insert 12 and the resonant cavity 14, the assembly fixture is equipped with a two-dimensional micro-drive device. This device can finely adjust the position of the coaxial insert 12 during assembly, ensuring that its distance relative to the cavity wall is within the design tolerance range. This effectively suppresses mode eigenvalue changes, decreased electron beam coupling efficiency, and increased stray radiation caused by misalignment.

[0144] After precise coaxial assembly, the gyrotron assembly needs to be quickly and reliably connected to the various support subsystems of the loading test platform. To this end, this invention integrates an integrated test interface unit into the loading test platform. This interface unit adopts a standardized design, centrally integrating various interfaces for interfacing with the power system 5, load system 6, cooling system 7, monitoring and diagnostic system 8, and control system 9. These include, but are not limited to: electrical interfaces for connecting high-voltage cables and signal cables to the cathode power supply, bulk power supply, filament power supply, and magnetic field power supply; fluid interfaces for connecting quick-connect fittings to the independent sub-circuits of the cooling system; and signal interfaces for connecting command lines, status feedback lines to the control system, and various sensor signal lines to the monitoring and diagnostic system. Through this integrated test interface unit, the assembled gyrotron assembly can be connected to the complete test environment in the shortest possible time, entering the commissioning and loading test state.

[0145] This invention fully considers the iterative characteristics of "design-test-optimization" in the development of gyrotrons. The gyrotron component loading system 2 supports the removal, modification, and reloading of components from the assembled unit. When a modular component is found to have performance that does not meet technical specifications during testing, it can be removed from the unit for design correction or process improvement. The corrected component can then be reloaded onto the test platform via the assembly tooling and interface unit for a new round of integration and performance verification. This design makes the loading test platform not only the operating environment of the gyrotron unit but also an integrated R&D infrastructure supporting the iterative upgrade of gyrotron components and accelerating technological breakthroughs.

[0146] (2) Strong magnet system 3

[0147] The high-power magnet system 3 is the core component that provides the gyrotron with a strong magnetic field that meets the resonant frequency and power requirements. Its basic physical principle is that the operating frequency of the gyrotron is proportional to the electron cyclotron frequency, which is determined by the magnetic field strength. Therefore, using a stronger magnetic field allows the gyrotron to operate at a higher frequency, thus meeting the demand for higher magnetic field strength in nuclear fusion devices. Simultaneously, a highly stable magnetic field is also crucial for maintaining electron beam quality and ensuring beam-wave interaction efficiency.

[0148] To meet the technical goals of a 2MW-class coaxial gyroscope with adjustable center frequencies of 170GHz and 240GHz, this invention employs a liquid helium-free cryogenic superconducting magnet system. Specifically, the design value of the central magnetic field strength of the superconducting magnet system is 6.7-10.5 Tesla (T), and the room temperature aperture of the magnet is 261 mm. This aperture size design fully considers the assembly requirements of the entire coaxial gyroscope—a sealed vacuum tube shell is placed inside the magnet aperture, with the bottom accommodating the cathode electron gun assembly that generates the electron beam, and the top accommodating the resonant cavity and quasi-optical output system. The magnet uses direct conduction cooling technology with a liquid helium-free refrigerator, eliminating the need for liquid helium immersion or frequent replenishment, significantly reducing operating and maintenance costs and complexity. Theoretical calculations show that this 10.5T-class superconducting magnet system can provide a stable, uniform, and high-precision axial guiding magnetic field for a 2MW-class coaxial gyroscope operating at frequencies up to 240GHz.

[0149] This invention integrates a multi-pole correction coil system within the superconducting magnet system as an actuator for precise alignment of the insert. In a preferred embodiment, this multi-pole correction coil system employs a bipolar coil (or dipole coil) configuration, such as a 3×4 coil array. This coil system is powered independently of the main magnet and is driven by an independent programmable, high-stability DC power supply. Its working principle is as follows: by precisely controlling the magnitude and direction of the current in each correction coil, a controllable, weak transverse correction magnetic field can be generated within the magnet aperture. This correction magnetic field interacts with the coaxial insert, generating a small transverse electromagnetic force, thereby achieving two-dimensional, micron-level displacement adjustment of the insert relative to the cavity axis. This ensures that the gyrotron always operates in its optimal mode, providing a crucial guarantee for achieving stable 2MW-level output in the 240GHz high-frequency band.

[0150] The superconducting magnet system is tightly integrated with the cooling system. The magnet's cold head is directly thermally connected to the refrigerator, and the cold shield and current leads are also equipped with dedicated cooling circuits. The entire magnet system is monitored and interlocked for safety by the main control system. Any signal indicating overrun, abnormal temperature, or cooling failure will trigger the system's emergency protection procedure to ensure device safety.

[0151] (3) Vacuum system 4

[0152] The vacuum system 4 uses a sputtering ion pump and a non-evaporative getter to maintain the gyrotube 1 at a pressure better than 10. -8 Operating at an ultra-high vacuum of mbar. To ensure low-loss transmission of millimeter waves within the waveguide and prevent air breakdown, a turbomolecular pump-based vacuum system is configured throughout the waveguide transmission link (from the output window to the load). This system can pump the vacuum level inside the waveguide to below 0.01 Pa, ensuring no ionization breakdown occurs within the waveguide under high-power continuous wave conditions and reducing atmospheric absorption losses. Simultaneously, an ultra-high vacuum environment must also be maintained inside the gyrotube to ensure normal electron beam emission and transmission, preventing ionization breakdown or cathode poisoning caused by collisions between residual gas molecules and electrons.

[0153] (4) Power supply system 5

[0154] The power system 5 is the core that provides energy to the gyrotron and enables precise control and protection. It is a complex, multi-level system whose design draws heavily on the latest advancements in modular power electronics technology, particularly the high power density, high efficiency, and high controllability advantages of solid-state transformer (SST) technology in high-voltage DC power supplies and data center power supplies. This invention applies this modular technology to the specific field of nuclear fusion heating sources, constructing a high-performance power supply that meets the specific requirements of a 2-megawatt gyrotron through the series combination of basic modules.

[0155] Electrical configuration and core power definition:

[0156] The operation of a gyrotron requires multiple power sources. The power supply configuration principle of this invention is as follows: Figure 14 As shown: The electron gun consists of a filament F and a cathode K. The filament F heats the cathode K, emitting electrons. The electrons are accelerated in the acceleration chamber, passing through the anode A and the body electrode B before reaching the resonant cavity. The electrons ultimately collide with the collector electrode C. The potential of the collector electrode C is lower than that of the body electrode B to slow down the electron velocity. The filament power supply FPS supplies power to the filament F, and the cathode power supply MPS provides a negative voltage between the collector electrode C and the cathode K, in the range of tens of kilovolts. The body electrode power supply BPS provides a positive voltage between the collector electrode C and the body electrode B, also in the range of tens of kilovolts. The anode power supply APS can selectively switch the voltage between the cathode K and the anode A, thereby regulating the beam current.

[0157] To drive the electron gun and establish an electron beam acceleration field, the system is equipped with the following special power supply group:

[0158] Cathode power supply MPS: such as Figure 15 As shown, the cathode power supply has its positive output grounded and its negative output connected to the cathode of the gyrotron, serving as the primary source of electron injection kinetic energy. The main power supply is rated at 60 kV DC and 100 amps, and is controlled by a thyristor.

[0159] Body power supply BPS: such as Figure 15 As shown, its positive terminal is connected to the body electrode of the gyrotube, and its negative terminal is grounded. This power supply provides an adjustable positive voltage between the body electrode and ground potential, with a typical design value of approximately 30 kV (which can be adjusted within a certain range as needed during actual operation). The total accelerating voltage is the sum of the absolute values ​​of the cathode power supply voltage and the body power supply voltage, with a typical value of approximately 80 kV.

[0160] DC magnetic field power supply: Used to provide the DC current required to generate a 6.7-10.5 Tesla magnetic field for the superconducting magnet. This power supply is independent of... Figure 15 The main circuit shown is directly connected to the superconducting magnet system.

[0161] Auxiliary power supply: This includes power supplies for the control system 9, cooling system 7, and other auxiliary equipment. These auxiliary power supplies are also independent of... Figure 15 The main circuit shown is distributed across various subsystems of the loading test platform.

[0162] A crucial parameter for gyrotron operation is the beam voltage between the cathode K and the body electrode B. Electrons are accelerated between these electrodes by this voltage, which determines their kinetic energy and the increase in relativistic mass. This increase in relativistic mass affects the electron's cyclotron frequency. The resonant cavity of a gyrotron typically has a high quality factor Q, meaning that even a small change in the cyclotron frequency significantly impacts the gyrotron's output power. Solid-state transformer DC power supplies can ensure the beam voltage is as precise as possible with minimal ripple.

[0163] Gyrotron high-voltage DC power supply system architecture:

[0164] The gyrotron high-voltage DC power supply system of this invention supports pulse and continuous wave modes. Its foundation and core is a pulse step modulator (PSM), and a DC / DC converter is added to improve flexibility, reliability and performance.

[0165] The high-voltage DC power supply system mainly consists of circuit breakers and contactors, three high-voltage units, a multi-winding high-voltage isolation transformer, a PSM module, an output voltage and current measurement and control box, and a control system. The main circuit structure of the high-voltage power supply is as follows: Figure 16As shown. Power is supplied from the mains. Each high-voltage unit includes a three-phase multi-winding transformer and 42 switching power supply modules. Each transformer has 42 windings on its secondary side to power the switching power supply modules. High-voltage circuit breakers provide power to the transformer and overcurrent protection; contactors enable soft-start power-on and reduce inrush current; multi-winding high-voltage isolation transformers provide individual power to the PSM modules while achieving high-voltage isolation for the system; output voltage and current measurement and control boxes detect and determine threshold values ​​for the high-voltage power supply output voltage and current, participating in logic protection; the control system monitors the entire high-voltage power supply system, selects the power supply operating mode, sets parameters, and interacts with the main control system of the gyrotube test bench to achieve various interlocking controls and rapid protection functions.

[0166] The control system calculates the number of rectifier modules to be activated based on the set voltage, then sequentially delays and alternately controls the conduction of the IGBTs inside the modules to establish high voltage. It adjusts the number of modules activated in real time based on the set and output voltage values, achieving power supply regulation within an 80kV / 100A range to meet the requirements of the electronic rotary heating system. This solution overcomes the shortcomings of traditional high-voltage DC power supplies, such as large unit size, low efficiency, grid-side low-order harmonic pollution, low power factor, large output ripple, and slow dynamic response. It possesses the dual advantages of steady-state voltage application and rapid modulation.

[0167] The gyrotron high-voltage DC power supply system of this invention can achieve the following key performance indicators: providing DC and pulse systems with a maximum voltage of 200 kV and a current of up to 2 kA; ​​the total system capacity is configured to be more than twice the rated power of the gyrotron, the output voltage stability is better than 0.1%, the redundant design improves reliability, the thermal module load is balanced, and the service life is long; the load short-circuit energy is <5 joules (<1 joule when operating with reverse voltage), the rise time is short (5 microseconds / 160 kV) and continuously adjustable; it is suitable for resistive loads, RF loads, megawatt-level continuous wave loads, and high peak power pulse modulator loads.

[0168] Body power supply and fast power modulation:

[0169] The bulk power supply (BPS) is specifically designed as a high-voltage amplifier. Its small-signal bandwidth is no less than 10 kHz, and its output voltage swing is no less than 15 kV. A fast high-voltage amplifier with a 30 kV voltage swing is used to stabilize the accelerating voltage and modulate the millimeter-wave power up to 10 kHz. By rapidly and precisely adjusting the bulk power supply voltage, deep modulation of the gyrotron's millimeter-wave output power can be achieved at a frequency of 10 kHz. Under typical operating conditions, a reduction in bulk voltage of approximately 15 kV can decrease the millimeter-wave power from 1 MW to 100 kW.

[0170] When performing wide-range power modulation, the control system will synchronously adjust the output voltage of the cathode power supply MPS and the bulk power supply BPS to ensure the stability of the collector potential while realizing rapid changes in millimeter-wave power, and prevent it from overloaded due to sudden current changes.

[0171] Fast protection switch:

[0172] The gyrotrobe is extremely sensitive to arcing within the waveguide. To limit energy deposition in the event of an internal arc, this invention incorporates a water-cooled IGBT fast protection switch connected in series in the high-voltage DC main circuit. The typical rated value is 100 kV DC, 100 Amperes. This switch is directly linked to a fast protection circuit based on a Field-Programmable Gate Array (FPGA). Upon detecting fault signals such as overcurrent or arcing, the protection circuit can drive the IGBT switch to disconnect the gyrotrobe from the power supply within 2 microseconds, ensuring that the energy deposited at the fault point is strictly limited to below 10 Joules. The system is also equipped with a solid-state circuit breaker to short-circuit the power supply in the event of a fault, forming multiple layers of protection.

[0173] Solid-state transformer technology:

[0174] The high-voltage DC power supply uses a solid-state transformer as the core technology of its modular switching power supply unit. A solid-state transformer is a power conversion device based on power electronics and high-frequency magnetic isolation technology. Through high-frequency and modular design, it achieves a significant improvement in power density and conversion efficiency.

[0175] The solid-state transformer used in this invention employs a wide-bandgap power semiconductor switch in its isolated DC / DC converter, increasing the operating frequency to the kilohertz or even megahertz level. Combined with an intermediate frequency transformer to replace the traditional power frequency transformer, it achieves electrical isolation while significantly reducing the volume of the magnetic core and windings, and significantly improving the power density.

[0176] like Figure 17 As shown, the solid-state transformer uses a three-stage circuit topology to achieve power conversion and isolation:

[0177] Medium-voltage stage: The medium-voltage stage is the grid interface of the solid-state transformer, employing a multi-H-bridge module cascaded topology. Each phase consists of the same number of cascaded power modules to withstand the input phase voltage, rectifying the three-phase medium-voltage AC power from the grid into stable high-voltage DC power. High-power Si IGBTs or SiC MOSFETs are used for the AC / DC stage power devices to achieve rectification and power factor correction. A filter inductor is connected between the mains power and the cascaded H-bridges to filter out high-frequency ripple in the input current and achieve a boost function.

[0178] Isolation Stage: The isolation stage is the core component of the solid-state transformer, enabling electrical isolation, voltage matching, and power regulation. It consists of two H-bridge circuits and a high-frequency transformer. The front-stage H-bridge inverts the high-voltage DC output from the medium-voltage stage into a high-frequency AC square wave, which is then coupled to the secondary side via the high-frequency transformer. The rear-stage H-bridge rectifies the high-frequency AC square wave into a stable low-voltage DC. The high-frequency transformer uses nanocrystalline or ferrite cores, and its volume is only one-tenth that of a traditional power frequency transformer, with an efficiency exceeding 98%. The DC / DC stage power devices use SiC MOSFETs, employing a dual active bridge or resonant topology to achieve soft switching and high-efficiency power transfer through resonant transformation.

[0179] Low-voltage stage: The low-voltage stage is the final output unit of the solid-state transformer facing the load. The output sides of each module are connected in series to meet the high voltage and high power requirements of the gyrotron high-voltage DC power supply. The low-voltage stage uses pulse width modulation (PWM) technology to convert the DC power output from the isolation stage into customized electrical energy required by the load, and has functions such as continuously adjustable output voltage, real-time voltage regulation, and current limiting protection.

[0180] For ease of deployment and testing, this invention can also employ a containerized integrated power supply solution. The complete power system described above is integrated into a standard weatherproof container, with prefabrication and commissioning completed at the factory. This solution improves the system's mobility and deployment flexibility, making it suitable for mobile test platforms or early demonstration projects.

[0181] (5) Cooling system 7

[0182] The cooling system 7 is the core guarantee for the stable operation of the 2MW-class long-pulse / continuous-wave gyrotron. The gyrotron and its power supply generate a huge amount of heat during operation, which must be effectively managed through a large-capacity cooling system to avoid equipment damage and maintain stable performance.

[0183] The cooling system 7 fully utilizes the modular characteristics of the gyrotube to design independent active cooling circuits for each key sub-component, including a water cooling system 71, a liquid helium-free cooling system 72, and an oil cooling system 73. Specifically: the liquid helium-free cooling system 72 provides cooling for the strong magnet system 3; the oil cooling system 73 provides cooling for the power system 5 and the parts of the electron gun 11 that are not suitable for water cooling.

[0184] This invention uses a megawatt-class water-cooled unit as the cold source for the cooling system. To ensure power supply reliability, the cooling system adopts a dual-power supply design, which can maintain normal operation of the cooling system even if either power supply circuit fails, thus avoiding equipment damage to the rotary tube due to cooling failure.

[0185] The cooling system 7 includes multiple independent sub-cooling circuits to independently cool and monitor the heat load of the electron gun 11, coaxial insert 12, beam channel 13, resonant cavity 14, quasi-optical transmission system mirror, mirror box 17, output window 18, and collector 19.

[0186] Figure 18 This embodiment demonstrates a cooling distribution system for a rotary tube, consisting of a main manifold and distribution manifolds. A stainless steel manifold connects the cooling water to the rotary tube distribution manifold and is divided into six main branches based on pressure and flow requirements, providing dedicated input and output interfaces for each cooling loop. Each loop is equipped with flow, temperature, and pressure monitoring sensors. All sensor parameters can be displayed locally and remotely monitored, acquired, and controlled via control system 9.

[0187] During long pulse and continuous wave operation, the control system 9 monitors the internal losses and heat load status of each component in real time through sensors distributed in each loop, and performs online evaluation of the overall energy balance of the gyrotube, providing a basis for optimizing and adjusting the operating parameters.

[0188] The resonant cavity 14 is the component with the highest power density and the greatest difficulty in thermal management within the gyrotube. Especially under high-power operating conditions where the maximum power density at the cavity center reaches 2 kW / cm², conventional cooling methods are insufficient to meet heat dissipation requirements. To address this, the present invention fills the space between the outer wall of the resonant cavity and the external water-cooling jacket with copper Raschig rings, forming a porous brazed structure with high thermal conductivity, thereby achieving efficient heat transfer.

[0189] The beam channel 13 is internally stacked with corrugated copper rings and damping ceramic rings. The corrugated copper rings are used to increase the heat transfer area and enhance the turbulent heat transfer effect; the damping ceramic rings also serve multiple functions such as structural support, vibration damping, and electrical insulation.

[0190] Cooling channel form: Spiral cooling channels are integrated inside and around the above-mentioned stacked structure, which allows the cooling medium to flow at high speed along the spiral path, significantly improving the local heat transfer coefficient.

[0191] Active cooling device: The spiral cooling channel is connected to the external cooling circuit to form a closed-loop active cooling system, which continuously removes the ohmic heat loss deposited on the cavity wall.

[0192] To accommodate the temperature differences and thermal expansion characteristics of different components during operation, this invention further designs an external water-cooling jacket that can move along the axis. This external water-cooling jacket surrounds the cavity and forms the outer flow channel of the cavity's cooling circuit.

[0193] The external water-cooling jacket is connected to the loading test platform via a mechanical guiding mechanism and is movable and adjustable along the axial direction. During the process of the rotary tube starting from a cold state to a thermal steady state, or when the temperature distribution of the cavity changes due to changes in operating power, the relative dimensional changes between the cavity and the external water-cooling jacket caused by thermal expansion mismatch can be actively compensated by adjusting the axial position of the external water-cooling jacket, thus maintaining the optimal cooling gap and avoiding local overheating or cooling dead zones.

[0194] In addition to the cavity, this invention also designs a special cooling solution for other components under high heat load:

[0195] Collector cooling: A multi-stage step-down collector structure is adopted, and each collection stage is equipped with an independent cooling circuit to effectively remove the electron beam deposition energy;

[0196] Output window cooling: The edge of the CVD diamond window is connected to the copper window frame by high-temperature brazing. The window frame is equipped with a water cooling channel to force cooling of the window edge and control the temperature difference between the center and edge of the window within the allowable range.

[0197] Mirror cooling: Each mirror in the quasi-optical transmission system has a cooling channel on its back to dissipate stray radiation power absorbed by the mirror surface. The overall heat dissipation capacity of the MOU unit reaches 80 kilowatts.

[0198] The cooling system of this invention, through a series of technical means such as dual-power redundant design, modular independent cooling circuit, enhanced heat exchange structure inside the cavity, and axially movable external water cooling jacket, constitutes a complete thermal management network covering all heat-generating components of the gyrotube, providing stable and reliable cooling guarantee for 2MW-level, long pulse / continuous wave operation.

[0199] (6) Millimeter-wave transmission link and load system 6

[0200] The load system 6 includes a dummy load 61 for testing and a real load 62 for connecting to the nuclear fusion device, used to simulate or bear the working load of the gyrotron 1 in an actual nuclear fusion device. Figure 19 As shown, this invention constructs a complete, high-power capacity millimeter-wave transmission link.

[0201] Radio frequency conditioning unit (MOU):

[0202] To meet the high-efficiency transmission requirements of 2MW-level, 170 / 240GHz high-frequency millimeter waves, and to ensure flexible alignment under different test conditions, this invention incorporates a radio frequency conditioning unit (MOU) after the gyrotron output window. For example... Figure 20 As shown, the radio frequency modulation unit (MOU) adopts an in-plane optical layout, consisting of a five-mirror system located on the same plane:

[0203] Plane mirror J1: Used to compensate for misalignment errors in the output beam of the gyrotube and to achieve initial optical path correction.

[0204] Secondary reflectors J2 and J5: Used to convert the high-order beam output from the gyrotron into the HE11 low-loss mode that matches the subsequent transmission line, ensuring transmission efficiency.

[0205] Grating polarizers J3 and J4: Composed of two gratings, used to adjust the polarization state of millimeter waves, while effectively reducing the peak power density of the mirror surface through optical path extension.

[0206] All mirrors are equipped with precision adjustment mechanisms. Plane mirror J1 and secondary reflectors J2 and J5 can be rotated and adjusted around two orthogonal axes, while grating polarizers J3 and J4 can rotate around an axis perpendicular to their respective mirror surfaces. This allows for flexible and convenient optical path alignment while maintaining high power capacity. After adjustment by the MOU, the gyrotron output power is injected into the subsequent waveguide transmission line with a coupling efficiency of no less than 96%. The mirrors and cavity walls integrated within the MOU are designed with independent active cooling circuits. The cooling system provides circulating cooling medium, stably dissipating the heat load of up to 80 kW generated inside the MOU due to stray radiation and ohmic losses, ensuring thermal stability and optical path pointing stability under long pulse and continuous wave operation.

[0207] Waveguide transmission line:

[0208] The millimeter wave, coupled via MOU, enters the main transmission link. The transmission link includes:

[0209] Corrugated waveguide: A vacuum corrugated waveguide approximately 3.5 meters long with an inner diameter of 63.5 millimeters, used to transmit millimeter waves to the terminal load with low loss. The corrugated waveguide structure also has good mechanical flexibility, which can absorb system thermal deformation and installation tolerances.

[0210] Bidirectional directional coupler: A bidirectional horseshoe-shaped directional coupler is integrated on the waveguide, with a coupling coefficient of approximately 80 dB. This coupler is used to extract minute forward and reflected wave signals from the main transmission line, enabling the detection and diagnostic system to monitor the instantaneous output power, reflected power, and oscillation frequency of the gyrotron in real time.

[0211] Waveguide Switch: A manually operated single-pole double-throw (SPDT) waveguide switch is located at the end of the waveguide, before the dummy load. This switch allows the millimeter-wave output to be switched between two load ports without disrupting the vacuum.

[0212] Port 1: Connected to a short-pulse dummy load (operating in a standard atmospheric pressure environment) for short-pulse operation testing during the initial commissioning phase of the gyrotube;

[0213] Port 2: Connected to a continuous wave dummy load for long pulse and continuous wave rated power operation testing.

[0214] To ensure low-loss transmission of millimeter waves within the waveguide and prevent air breakdown, a turbomolecular pump (TMP)-based vacuum system is configured throughout the entire waveguide transmission link (from the output window to the load). This system can pump the vacuum level inside the waveguide to below 0.01 Pa, ensuring that ionization breakdown does not occur within the waveguide under high-power continuous wave conditions and reducing atmospheric absorption loss.

[0215] Dummy load:

[0216] Continuous Wave Dummy Load: Employing a water-cooled, fully absorbent load design, it possesses the full power absorption capability to withstand 2MW-level continuous wave operation. The load features an optimized water flow channel connected to the high-flow-rate deionized water circuit of the cooling system, and the average output power of the rotary tube is accurately measured using calorimetry.

[0217] Short pulse dummy load: A special short pulse absorption load under atmospheric pressure is used, which is suitable for power measurement in the initial commissioning stage of gyrotubes (narrow pulse width and low duty cycle), and can be used in conjunction with pulse integration technology to estimate peak power.

[0218] The load system and millimeter-wave transmission link of this invention, through the integration of multiple technical means such as high-efficiency MOU optical path matching, low-loss corrugated waveguide transmission, flexible dual load switching, high-precision directional coupling monitoring, and high vacuum maintenance, provide a complete, reliable, and high-precision testing environment from the output window to the terminal load for 2MW-class, 170 / 240GHz high-frequency gyrotrons, strongly supporting all technical solutions for the performance evaluation of the gyrotron and the realization of the testing and diagnostic system functions.

[0219] (7) Monitoring and Diagnostic System 8

[0220] The monitoring and diagnostic system 8 is the core measurement unit of the gyrotron loading test platform, used to perform full-parameter characterization and performance evaluation of the millimeter-wave beam output by the gyrotron. To meet the testing requirements of 2MW-class, 170 / 240GHz high-frequency gyrotrons under long-pulse and continuous-wave operating conditions, this invention constructs a complete diagnostic system covering three core indicators: power, frequency, and mode purity.

[0221] Output power measurement and monitoring:

[0222] For long-pulse and continuous-wave operating conditions, calorimetry is used as the absolute measurement method for output power. The continuous-wave dummy load has an optimized water flow channel inside, which is connected to the high-precision deionized water circuit of the cooling system. By measuring the temperature difference and water flow rate at the inlet and outlet of the dummy load water circuit, the average output power of the rotary tube is obtained through reliable calorimetric calculation.

[0223] To monitor the dynamic changes in the output power of the gyrotron in real time, this invention installs a calibrated Schottky diode detector at the output port of the directional coupler of the waveguide transmission line. The detector converts the coupled radio frequency signal into a voltage signal proportional to the instantaneous power, which is then sent to the control system via a data acquisition system to achieve continuous monitoring of the instantaneous radio frequency power.

[0224] During the initial short-pulse debugging phase of the gyrotron development, a short-pulse dummy load was used, along with pulse integration technology for power estimation. The pulse waveform was captured by a high-speed detector, and the pulse energy was integrated to calculate and invert the peak pulse power.

[0225] Output frequency measurement:

[0226] The operating frequency of the gyrotron directly determines the deposition location of millimeter waves in fusion plasma. This invention employs a spectrum analyzer for frequency measurement. By appropriately connecting the sampling port of the directional coupler to the spectrum analyzer, the spectral distribution of the gyrotron output signal is acquired and displayed in real time, and the center frequency value is directly read. Through real-time frequency measurement within an appropriate frequency range, frequency shifts and gyrotron deviance oscillations can be effectively detected.

[0227] Output mode purity diagnosis:

[0228] To minimize waveguide transmission line and coupling losses, the purity of the gyrotron output beam modes should be around 95%. This invention employs a non-contact measurement technique for mode purity assessment. This method measures the amplitude distribution of the high-power RF beam at different propagation distances, uses the amplitude information combined with phase retrieval technology to determine the phase distribution, and then estimates the mode content and purity of the output beam based on the obtained amplitude and phase distributions. This non-contact diagnostic method does not require intrusion into the high-power beam and can operate online at full power in continuous wave conditions, providing a basis for assessing the purity of gyrotron output modes.

[0229] (8) Control system 9

[0230] The control system 9 is the core command and decision-making center of the loading test system, responsible for coordinating the orderly operation of all subsystems, ensuring test safety, and achieving precise energy output of the gyrotron under complex operating conditions. The control system of this invention adopts a hierarchical distributed architecture, encompassing both global monitoring and slow interlocking at the test platform level, and embedding fast control and protection units with microsecond-level response capabilities for high-power supplies. Figure 21 As shown, its hardware components include a host computer and human-computer interaction software, a logic controller, a pulse controller, and interface circuits.

[0231] The host computer runs on an industrial control computer, providing a graphical human-machine interface. Operators can select the system's operating mode (such as short pulse debugging, long pulse operation, continuous wave operation, power modulation test, etc.) and set all operating parameters via a local computer located on-site or a remote computer on a test bench. These parameters include the target value of the accelerating voltage, the modulation waveform and amplitude of the body power supply, the magnetic field current, the cooling system temperature threshold, and the fault protection settings. All parameters are transmitted to the logic controller and pulse controller via serial communication.

[0232] The logic controller, implemented based on a programmable logic controller (PLC) or a high-performance industrial microprocessor, is the core execution unit of the main control layer. Its main functions include:

[0233] Status monitoring and slow-speed interlocking: Real-time acquisition of analog and digital signals such as temperature, pressure, flow rate, and vacuum level across the system via remote expansion modules. This includes water temperature, pressure, and flow rate parameters for each loop of the cooling system, vacuum level of the vacuum system, and operating status of the auxiliary power supply. The logic controller, based on preset safety thresholds, automates the management of system start / stop sequences, cooling and vacuum system interlocking, and auxiliary power supply control.

[0234] Signal and command blocking: The logic controller stores information about external devices and the status of power supply operation. When it detects that the system is in an unsafe state (such as insufficient cooling water flow or vacuum failure), it can block subsequent power supply operation commands and various control signals to prevent high voltage from starting under abnormal conditions.

[0235] Fault signal processing: Latch and report fault signals from each subsystem, and participate in the judgment of slow protection logic.

[0236] The pulse controller is the key unit for achieving high-precision, high-speed power supply control in this invention, and it is constructed using a field-programmable gate array (FPGA). Its core tasks include:

[0237] Precision timing control: Receives voltage commands from the logic controller and decomposes them into precise switching control sequences for nearly a hundred Pulse Step Modulation (PSM) modules. The pulse controller achieves smooth high-voltage establishment and rapid adjustment by delaying and interleaving the on / off states of the IGBTs within each PSM module. The on / off interval of each module is continuously adjustable within the range of 1 microsecond to 1 second, with timing control accuracy reaching 1 microsecond, thereby ensuring high stability and low ripple of the high-voltage power supply output.

[0238] Fast power modulation: The pulse controller simultaneously generates a fast analog reference signal (0-10VDC) to drive the power supply as a high-voltage amplifier. The frequency and amplitude of this reference signal are controlled by modulation parameters set by the host computer, enabling the power supply to achieve an output voltage swing of not less than 15 kV at a frequency of not less than 10 kHz, thereby achieving deep and fast linear modulation of the millimeter-wave output power of the gyrotron;

[0239] Digital and analog interfaces: The digital inputs of the pulse controller are used to receive status signals (such as module faults, abnormal temperatures) and external rapid fault signals from each PSM module; the digital outputs are used to generate switching control signals for the PSM modules; the analog inputs are used to receive external 0-10VDC voltage signals (such as real-time feedback from the diagnostic system); the analog outputs are used to output 0-10VDC voltage signals (such as for recording or forwarding to other subsystems).

[0240] To achieve safe isolation between the low-voltage control circuit and the high-voltage power circuit, and to enhance the system's electromagnetic interference resistance, all switching control signals, module status signals, and fast fault protection signals of the PSM modules are converted into optical signals via an interface circuit and transmitted using optical fiber. The photoelectric signal conversion interface circuit enables reliable connection and complete electrical isolation between the controller and the high-voltage equipment.

[0241] The control system of this invention has a multi-level, highly redundant fault protection system, among which rapid hardware protection is its core safety barrier:

[0242] Rapid Fault Detection: The pulse controller (FPGA) directly monitors critical fault signals from the power system and the gyrotron body via hardwired connections, including output overvoltage, dual output overcurrent, gyrotron body faults (such as arcing and overcurrent), and crowbar activation triggering. The control system can determine various system faults, including short circuits, within less than 20 microseconds.

[0243] Rapid protection execution: Once a fault is confirmed, the pulse controller immediately triggers the protection action, blocking the drive pulses of all PSM modules within microseconds and directly driving the fast protection switch connected in series in the high-voltage DC main circuit to disconnect the circuit. This fast protection switch is a water-cooled IGBT switch with a rated voltage of not less than 100 kV DC and a rated current of not less than 100 Amps. The total time from the occurrence of the fault to the complete disconnection of the main circuit is strictly controlled within microseconds, ensuring that the energy deposited at the fault point (such as the arc point in the waveguide) is less than 10 Joules, thereby effectively protecting the expensive high-power gyrotron from damage;

[0244] Slow-speed and emergency protection: In addition to fast hardware protection, the logic controller (PLC) layer also implements slow-speed interlock protection for output overvoltage and overcurrent. The system also has a hard-wired manual emergency stop button, which can trigger an emergency stop with the highest priority under any circumstances.

[0245] The control system and power supply system work in deep coordination. During large-amplitude power modulation, the control system synchronously adjusts the output voltage of the cathode power supply and the bulk power supply. While achieving rapid changes in millimeter-wave power (modulation capability of not less than 1kHz), it ensures the stability of the collector potential and prevents it from overloading due to sudden current changes.

[0246] The logic controller is based on a programmable logic controller. It monitors the temperature, pressure, and flow parameters of the cooling system in real time through a remote expansion module (ET 200M), and realizes the start-up and shutdown of the cooling system, the switching of the cooling circuit, and the fault interlock according to the preset algorithm.

[0247] The control system of this invention adopts a three-layer architecture of upper computer instruction issuance, logic controller platform coordination, and FPGA pulse controller precision execution and fast protection. Combined with all-fiber high-voltage isolation technology, it successfully solves the special requirements of PSM high-voltage power supply for multiple controlled objects, complex control process, high operating speed and accuracy requirements, and adaptation to multiple operating modes. It realizes stable, reliable, on-demand and safe control of the 2MW-level high-frequency gyrotron loading test process.

[0248] In summary, this invention, through the innovative component design of the gyrotron body and the systematic construction of the loading test platform, not only provides a specific technical solution for a gyrotron that can reach 2MW, 170 / 240GHz, with adjustable frequency and support for long pulse operation, but more importantly, it provides an "integrated" infrastructure that can support the entire process of this high-end device from research and development, testing to iterative maturity, effectively solving the integrated testing bottleneck in the development of complex systems.

[0249] For those skilled in the art, various improvements and modifications can be made without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. The above descriptions are merely preferred embodiments of this invention and do not limit the patent scope of this invention. Any equivalent structural or procedural transformations made based on the description and drawings of this invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this invention.

Claims

1. A continuous-wave, high-power, frequency-tunable gyrotron loading test system for nuclear fusion, characterized in that, include: The gyrotube (1) is a coaxial gyrotube, which includes an electron gun (11), a coaxial insert (12), a beam channel (13), a resonant cavity (14), a transmitter (15), a quasi-optical transmission system (16), a mirror box (17) and an output window (18), and a collector (19). The output power is 2 megawatts, the center frequency is 170 GHz or 240 GHz and the frequency is adjustable, and it supports a long pulse operation mode with a pulse width of not less than 1 second and a continuous wave operation mode. The loading test platform is connected to the gyro tube (1) to form an integrated test system, which is used to support the full life cycle test verification of the gyro tube (1) from joint research and manufacturing, factory testing to access nuclear fusion test and operation and maintenance; The loading test platform is configured to adaptably provide corresponding power supply, cooling, magnetic field and load conditions according to the test requirements of different models of gyrotubes (1). It includes a gyrotube component loading system (2), a strong magnet system (3), a vacuum system (4), a power supply system (5), a load system (6), a cooling system (7), a monitoring and diagnostic system (8) and a control system (9). The gyro tube component loading system (2) is used to precisely align the modular gyro tube (1) components coaxially and assemble them into a complete gyro tube machine. The strong magnet system (3) is used to provide the gyrotube (1) with a strong magnetic field that meets the requirements of resonance frequency and power; The vacuum system (4) uses a sputtered ion pump and a non-evaporative getter to maintain the gyrotube (1) at a pressure better than 10. -8 The ultra-high vacuum operating state of mbar is used to prevent gas ionization, high voltage breakdown and cathode poisoning. The power system (5) is used to provide power to the gyrotube test specimens with different power levels and modulation requirements and the loading test platform itself; The load system (6) includes a dummy load (61) for testing and a real load (62) connected to the nuclear fusion device to simulate or carry the working load of the gyrotube (1) in an actual nuclear fusion device. The cooling system (7) includes multiple independent sub-cooling circuits to independently cool and monitor the heat load of the electron gun (11), coaxial insert (12), beam channel (13), resonant cavity (14), quasi-optical transmission system mirror, mirror box (17), output window (18) and collector (19) of the gyrotube (1). Each branch is equipped with flow, temperature and pressure sensors. The beam channel (13) is internally stacked with corrugated copper rings and shock-absorbing ceramic rings, and integrated with a spiral cooling channel, so that the cooling medium flows along the spiral path to enhance heat transfer and suppress vibration. The cooling system (7) also includes an external water-cooled jacket surrounding the resonant cavity (14); the external water-cooled jacket is connected by an axial drive mechanism so that it can move along the axial direction of the resonant cavity (14) to accommodate the temperature and thermal expansion coefficient differences of different components during operation; the cooling of the resonant cavity (14) is achieved by a Raschig ring or microchannel cooling structure filled between its outer wall and the external water-cooled jacket; The inner wall of the mirror box (17) is lined with a water-cooled ceramic tube (171) to absorb stray radiation generated during quasi-optical transmission. The collector (19) is a multi-stage step-down collector, with each stage having an independent cooling circuit; The monitoring and diagnostic system (8) is used to monitor and diagnose the operating conditions and parameters of the rotary tube (1) and its components; The control system (9) is used for coordinated control, status monitoring, safety interlocking and fault protection of the loading test platform.

2. The gyrotube loading test system according to claim 1, characterized in that, The gyrotube component loading system (2) includes: Modular component alignment and assembly fixtures are used to achieve precise coaxial positioning and fixation of the electron gun (11), coaxial insert (12), beam channel (13), resonant cavity (14), quasi-optical transmission system (16) and collector (19); The integrated test interface unit integrates standardized electrical, fluid and signal interfaces that interface with the power system (5), cooling system (7), load system (6), control system (9) and monitoring and diagnostic system (8) for joint debugging and load testing of the assembled gyrotube (1).

3. The gyrotube loading test system according to claim 1, characterized in that, The strong magnet system (3) is a liquid helium-free superconducting magnet system with a magnetic field strength of 6.7-10.5 Tesla; the superconducting magnet system is also equipped with a multi-pole correction coil system for providing precise alignment of the coaxial insert (12).

4. The gyrotube loading test system according to claim 1, characterized in that, The electron gun (11) includes a reverse magnetron injection gun (113) mounted at the bottom and a magnetron injection gun (112) at the top. The anode and cathode profiles of the magnetron injection gun (112) are configured to suppress electron beam corona and secondary electron generation. The emitter of the magnetron injection gun (112) adopts an emission ring structure to reduce the impact of manufacturing and alignment tolerances of the emitter and its adjacent components on the performance of the gyrotube. The edge of the emission ring is coated with an anti-emission material (111). The heat-sensitive components in the electron gun (11) are equipped with a direct cooling structure. The coaxial insert (12) is installed at the lower center of the gyrotube (1), and its position is adjusted relative to the cavity wall of the resonant cavity (14) by a two-dimensional micro-drive device so that the concentricity of the coaxial insert (12) and the resonant cavity (14) meets the design requirements.

5. The gyrotube loading test system according to claim 1, characterized in that, The resonant cavity (14) includes an input conical section, a cylindrical interaction region, and an output conical section; the outer wall of the resonant cavity (14) is provided with mode conversion ripples.

6. The gyrotube loading test system according to claim 1, characterized in that, The collector (19) is a multi-stage step-down collector based on the E×B drift concept; the multi-stage step-down collector includes multiple collection stages separated by conical spiral grooves, which are used to generate the angular component of the electric field to cooperate with the axial magnetic field to realize the E×B drift of the electron beam.

7. The gyrotube loading test system according to claim 1, characterized in that, The output window (18) is a chemical vapor deposition diamond Brewster angle window with a diameter of not less than 180 mm and a thickness of not less than 2 mm, and is installed at a Brewster angle.

8. The gyrotube loading test system according to claim 1, characterized in that, The power supply system (5) includes: a cathode power supply and a body power supply that provide accelerating voltage; a DC magnetic field power supply for providing the strong magnet system (3) with the magnetic field required to generate a magnetic field of 6.7-10.5 Tesla; and an auxiliary power supply for powering the control system (9), the cooling system (7) and other auxiliary equipment. The negative terminal of the cathode power supply is connected to the cathode of the gyrotube (1), and the positive terminal is connected to the collector and grounded; the power supply establishes a main accelerating negative high voltage of -55kV to -85kV between the cathode and the collector, with a current of 45-100 amperes, and is controlled by a thyristor. The negative terminal of the body power supply is grounded, and the positive terminal is connected to the body electrode. A positive voltage of +25kV to +35kV is provided between the collector and the body electrode. The body power supply is configured as a high-voltage amplifier with a bandwidth of not less than 10 kHz and an output voltage swing of not less than 15 kV. It is used to modulate the radio frequency output power of the gyrotron (1) at a frequency of 10 kHz by adjusting its output voltage. The sum of the absolute values ​​of the cathode power supply voltage and the body power supply voltage together constitutes the accelerating voltage of the gyrotube (1); the total accelerating voltage can be finely adjusted by independently adjusting the body power supply voltage; low modulation amplitude can be achieved by controlling the body power supply voltage alone, while large amplitude power modulation requires synchronous modulation of the cathode power supply and body power supply voltage to prevent collector overload. When performing wide-range power modulation, the control system (9) synchronously adjusts the output voltage of the cathode power supply and the body power supply. While realizing the rapid change of the radio frequency power of the gyrotube (1), it ensures the stability of the collector potential and prevents it from being overloaded due to sudden current changes. The cathode power supply adopts pulse step modulation technology and is composed of multiple modular switching power supply units based on solid-state transformers connected in series. Its total capacity is more than twice the rated power of the gyrotron (1), and the output voltage stability is better than 0.1%. The solid-state transformer uses a wide bandgap power semiconductor switch for its isolated DC-DC converter, and the operating frequency is increased to the kilohertz or even megahertz level.

9. The gyrotube loading test system according to claim 1, characterized in that, The cooling system (7) is a megawatt-level active cooling system, including a water cooling system (71), a liquid helium-free cooling system (72), and an oil cooling system (73), wherein: the liquid helium-free cooling system (72) is used to provide cooling for the strong magnet system (3); the oil cooling system (73) is used to provide cooling for the power supply system (5) and the parts of the electron gun (11) that are not suitable for water cooling; the cooling system (7) adopts dual power supply.

10. The gyrotube loading test system according to claim 1, characterized in that, The monitoring and diagnostic system (8) includes: The power measurement unit is used to measure the output power of the gyrotube (1) by calorimetry and to monitor the instantaneous radio frequency power by means of a directional coupler and a detector; A frequency measurement unit for measuring radio frequency via a spectrum analyzer connected to a directional coupler; The mode purity analysis unit is used to acquire the amplitude and phase distribution of the radio frequency beam through non-contact measurement technology, and to evaluate the purity of the output mode accordingly.

11. The gyrotube loading test system according to claim 8, characterized in that, The control system (9) includes: The host computer and human-computer interaction software are used to select the working mode and set the operating parameters through a local or remote computer. The logic controller is used to process information from external devices, power supply status, cooling system status, and vacuum system status, and to implement logical blocking of various control signals and commands. The pulse controller, based on a field-programmable gate array, is used to perform precise timing control on and off of multiple pulse step modulation modules in the power system (5), and the control interval is adjustable in the range of 1μs to 1s. The interface circuit is used to convert the switching control signal and fault protection signal of the pulse controller into optical signals and transmit them through optical fiber to achieve high-voltage isolation between the controller and the high-voltage equipment. The control system (9) is configured to have rapid fault detection and execution capabilities, and can complete the judgment of system faults, including short circuits, within less than 20 microseconds and trigger protection actions; the protection actions include triggering the fast protection switch disconnection circuit connected in series in the high-voltage circuit; the fast protection switch is a water-cooled IGBT switch with a rated voltage of not less than 100 kV DC and a rated current of not less than 100 Amperes; the total time from fault detection to main circuit disconnection is within a few microseconds, so that the energy deposition at the fault point is less than 10 Joules; The control system (9) is also used to generate control signals to drive the body power supply as a high voltage amplifier to achieve modulation of the millimeter wave output power of the gyrotube (1) at a frequency not lower than 1kHz. The logic controller is based on a programmable logic controller. It monitors the temperature, pressure and flow parameters of the cooling system (7) through a remote expansion module and is used to realize the system start-stop sequence, interlocking of the cooling and vacuum systems, fault signal latching and blocking of power operation commands. The control system (9) also integrates at least three fault protection mechanisms, including output overvoltage protection, dual output overcurrent protection, rotary tube fault protection, crowbar action protection, and manual emergency stop protection.

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