W-band microwave reflectometer for high-heat-load plasma superconducting linear device and measuring method of W-band microwave reflectometer

Abstract

The invention discloses a W-band microwave reflectometer for a high-heat-load plasma superconducting linear device and a measuring method of the W-band microwave reflectometer, and belongs to the technical field of plasma diagnosis. The signal source unit is used for generating a transmitting signal; the transmitting unit is used for dividing a transmitting signal into two paths; the transmission unit is used for dividing the emission signal into a reference signal and a detection signal, sending the detection signal to the plasma and transmitting a reflection signal reflected from the plasma to the signal processing unit; the signal processing unit is used for amplifying the reflected signal and ensuring unidirectional transmission of the signal; and the frequency mixing unit is used for performing first-time frequency mixing on the reflected signal and the reference signal to obtain an intermediate frequency signal, and performing second-time frequency mixing on the intermediate frequency signal and the crystal oscillator reference signal to obtain I and Q signals. The method is used for overcoming the defects that in existing plasma density diagnosis, real synchronous measurement cannot be achieved in an O / X mode, the system is complex, the signal-to-noise ratio is low, and the integration degree is low.

Description

Technical Field

[0001] This invention belongs to the field of plasma diagnostic technology, specifically relating to a W-band microwave reflectometer for a high-heat-load plasma superconducting linear device and its measurement method. Background Technology

[0002] In magnetic confinement fusion and plasma property research, electron density is one of the key parameters determining plasma properties and behavior. Measuring its density profile is crucial for studying plasma confinement, stability, and transport phenomena. Microwave reflectometer technology, as a non-invasive plasma density profile diagnostic tool, is widely used in laboratory plasma density measurements. The working principle of a frequency-modulated continuous-wave microwave reflectometer is as follows: a continuously varying microwave signal is emitted into the plasma. When the frequency of the electromagnetic wave equals the cutoff frequency corresponding to a specific density in the plasma, it will be reflected. By measuring the phase difference between the reflected wave signal and the emitted signal, the location of the cutoff layer and the density information at that location can be calculated. Furthermore, the entire plasma density profile can be reconstructed using an inversion algorithm.

[0003] Since the spatial resolution of a microwave reflectometer is directly proportional to its sweep bandwidth, the development of high-frequency microwave reflectometer technology is inevitable in order to achieve higher spatial resolution and measure higher density ranges. However, existing microwave reflectometer technology, especially in the high-frequency band, faces several mutually restrictive technical bottlenecks: 1. Measurement Accuracy and System Complexity Issues of Dual-Antenna Systems: To achieve transmit-receive isolation, traditional microwave reflectometers typically employ a dual-antenna system, with one antenna transmitting the signal and the other receiving the reflected signal. While this approach ensures that the transmitted and received signals do not interfere with each other, it has some inherent drawbacks: First, the system has low integration, occupies a large space, and is costly. The dual-antenna design is difficult to deploy when the optical window size is small, limiting the band expansion. Second, precise alignment is difficult during antenna installation; even a small angular error between the two antennas can introduce phase measurement errors, affecting the density inversion accuracy. Finally, there is inevitably an angular difference between the two antennas, making it difficult to ensure that the same position is measured, leading to inherent biases in the results.

[0004] 2. Spectral purity and spurious signal issues: In the selection of microwave sources, existing solutions often use voltage-controlled oscillators for direct frequency multiplication or ordinary mixers for frequency conversion. These solutions generate spurious signals such as image frequencies and local oscillator leakage, causing interference: First, image frequencies will form interference signals at the receiver, leading to distance ambiguity and making it difficult to distinguish the true and false cutoff layers; second, spurious signals will increase system noise, making reflected signals difficult to distinguish; finally, in order to suppress these spurious signals, it is usually necessary to use filtering devices such as bandpass filters after the mixer, which is not only costly but also introduces additional insertion loss and phase nonlinearity.

[0005] 3. Problems with O-mode and X-mode measurements in the presence of a magnetic field: Existing solutions typically use a single linearly polarized antenna, controlling the antenna's polarization direction via a mechanical switch to measure O-mode and X-mode in a time-division manner. First, this temporal asynchrony results in a time difference in the plasma density information obtained in the two modes, making it impossible to reconstruct density profiles at the same moment for mutual reference. Second, switching polarization requires the introduction of additional components, increasing the system's cost, size, and complexity, and also introducing issues such as mechanical aging and switching speed. Finally, some solutions choose to directly build two independent microwave reflectometer systems for O-mode and X-mode, which avoids switching, but makes it difficult to ensure precise time synchronization between the two systems, and the hardware construction cost increases exponentially.

[0006] Therefore, existing technological approaches struggle to provide a solution that simultaneously achieves high spatiotemporal resolution, high integration, and high precision. Furthermore, on the high-heat-load plasma superconducting linear inductively coupled plasma (HIT-PSI) experimental platform simulating the extreme environment of a future fusion reactor divertor, plasma beam densities can reach 10-1. 21 m -3 The magnitude is greater than 2 T, the axial magnetic field exceeds 2 T, and the heat flux load is greater than 10 MW·m. -2 High-density plasmas require reflectometers to operate at higher frequencies, and strong magnetic field environments demand excellent anti-magnetic interference capabilities and stable O / X mode synchronous measurement capabilities. Therefore, there is an urgent need for a microwave reflectometer system that can be matched with a high-heat-load plasma superconducting linear device platform. The purpose of this invention is to overcome this technical barrier and provide a new method for achieving simultaneous, rapid, accurate, and continuous frequency sweep measurement of both O and X modes within a single system architecture. Summary of the Invention

[0007] This invention provides a W-band microwave reflectometer and measurement method for a high-heat-load plasma superconducting linear device, which solves the shortcomings of existing plasma density diagnostics, such as the inability to truly synchronize O / X modes, system complexity, low signal-to-noise ratio, and low integration.

[0008] This invention is achieved through the following technical solution: A W-band microwave reflectometer for a high-heat-load plasma superconducting linear device, the W-band microwave reflectometer comprising a signal generation unit, a transmission unit, a signal processing unit, and a mixing unit; The signal source unit is used to generate the transmitted signal; The transmitting unit is used to split the transmitted signal into two paths, one for O mode and the other for X mode, and multiply the two paths to obtain the detection signal. The transmission unit is used to divide the transmitted signal into a reference signal and a detection signal, send the detection signal to the plasma, and transmit the reflected signal reflected back from the plasma to the signal processing unit. The signal processing unit is used to amplify the reflected signal and ensure unidirectional signal transmission; The mixing unit is used to perform a first mixing of the reflected signal and the reference signal to obtain an intermediate frequency signal, and to perform a second mixing of the intermediate frequency signal and the crystal oscillator reference signal to obtain I and Q signals.

[0009] Furthermore, the signal generating unit is connected to the transmitting unit and the mixing unit respectively, the mixing unit is also connected to the signal processing unit, the transmission unit, the acquisition card and the computer respectively, and the transmission unit is also connected to the transmitting unit, the signal processing unit and the plasma respectively.

[0010] Furthermore, the signal source unit includes a crystal oscillator module and a VCO module; the crystal oscillator module is used to output a crystal oscillator signal; the VCO module is used to generate a transmission signal. The crystal oscillator module includes a crystal oscillator and a frequency multiplier. The crystal oscillator outputs a 100 MHz crystal signal and divides the crystal signal into four paths: one crystal signal is output to the intermediate frequency port of the single-sideband modulator; one is output to the external reference clock input of the data acquisition card for synchronous frequency sweep timing; the other two crystal signals are multiplied by a sixth frequency multiplier to generate a 600 MHz signal, which is output to the mixing unit as the reference signal for the IQ mixer. The frequency multiplier is used to multiply the output crystal oscillator signal to 600 MHz to obtain the crystal oscillator signal; The VCO module includes a signal generator and a voltage-controlled oscillator (VCO); the signal generator is used to generate a sawtooth wave signal to drive the VCO. The voltage-controlled oscillator generates a linear sweep frequency signal of 12.4-18.3 GHz under the drive of the sawtooth wave signal and the synchronization of the crystal oscillator, and the output terminal is connected to the local oscillator port of the single sideband modulator. The signal generated by the voltage-controlled oscillator and the crystal oscillator signal are mixed by a single-sideband modulator to obtain a pure 12.5-18.4 GHz single-sideband signal.

[0011] Furthermore, the transmitting unit includes a power divider and a frequency multiplier; the power divider is used to divide the 12.5-18.4 GHz transmitted signal of the signal source unit into two equally distributed paths. The frequency multiplier is used to multiply the transmitted signal to 75-110.4 GHz, which are used as the transmitted signals for mode O and mode X, respectively.

[0012] Furthermore, the transmission unit includes a directional coupler I, a directional coupler II, and a dual-polarized antenna; the directional coupler I is used to split the signal into two paths, with the main output terminal of the directional coupler I outputting a detection signal to the directional coupler II, and the other coupling terminal outputting a reference signal to the mixing unit; The detection signal of the directional coupler II is input from the coupling end and output from the input end to the dual-polarized antenna. The reflected signal is input from the dual-polarized antenna to the input end and output from the output end to the signal processing unit.

[0013] Furthermore, the mixing unit includes an amplifier, an IQ mixer, and a mixer; the amplifier is used to amplify the power of the crystal oscillator signal to drive the IQ mixer; The mixer is used to down-convert the reflected signal and the reference signal to obtain an intermediate frequency signal. The reflected signal after passing through the isolator is input to the RF port of the mixer, and the reference signal from the directional coupler 1 is input to the local oscillator port of the mixer. The IQ mixer is used to mix the intermediate frequency signal output by the mixer with the crystal oscillator reference signal to obtain I and Q signals. The intermediate frequency signal of the mixer is input to the intermediate frequency port, the 600 MHz reference signal from the crystal oscillator is input to the local oscillator port, and the output I and Q signals are input to the acquisition card for synchronous digitization.

[0014] Furthermore, the 100 MHz crystal oscillator is connected to hexadecimal generator I, hexadecimal generator II, and single-sideband modulator, respectively. The single-sideband modulator is also connected to voltage-controlled oscillator (VCO) and power divider, respectively. The VCO is connected to a signal generator. The power divider is connected to hexadecimal generator III and hexadecimal generator IV, respectively. Hexadecimal generator III is connected to directional coupler I-1. Hexadecimal generator IV is connected to directional coupler I-2. Directional coupler I-1 is connected to directional coupler II-1. Directional coupler I-2 is connected to directional coupler II-2. The sixth frequency multiplier I is connected to amplifier I, amplifier I is connected to IQ mixer I, and IQ mixer I is connected to mixer I and the acquisition card respectively; mixer I is connected to directional coupler I-1 and isolator I respectively, isolator I is connected to low noise amplifier I, low noise amplifier I is connected to directional coupler II-1, and directional coupler II-1 is connected to dual-polarized antenna; The sixth frequency multiplier II is connected to amplifier II, amplifier II is connected to IQ mixer II, IQ mixer II is connected to mixer II and acquisition card respectively; mixer II is connected to directional coupler I-2 and isolator II respectively, isolator II is connected to low noise amplifier II, low noise amplifier II is connected to directional coupler II-2, and directional coupler II-2 is connected to dual-polarized antenna.

[0015] A measurement method for a W-band microwave reflectometer used in a high-heat-load plasma superconducting linear apparatus, characterized in that the measurement method uses the W-band microwave reflectometer described above for a high-heat-load plasma superconducting linear apparatus, and the measurement method specifically comprises: The signal generator outputs a sawtooth wave, which, under the combined action of the sawtooth wave and the crystal oscillator, drives the voltage-controlled oscillator to generate a signal, resulting in an upper sideband swept electromagnetic wave signal and two reference signals. The swept-frequency electromagnetic wave signal is split into an input mixer as a reference signal and an input dual-polarized antenna detection signal after passing through a directional coupler. The dual-polarized antenna transmits the detection signal, which passes through the plasma, isolator, and mixer to obtain two signals, I and Q. These signals are then input into the acquisition card and converted into digital signals. Data processing is then performed to reconstruct the plasma density profile.

[0016] Furthermore, a signal generator is first used to output a sawtooth wave, which controls a voltage-controlled oscillator (VCO) and a 100 MHz crystal oscillator to continuously sweep frequencies within the 12.4-18.3 GHz range with a period of 20 μs. The signal emitted by the VCO and the 100 MHz crystal oscillator is split into three paths. One path, along with the VCO sweep signal, is input to a single-sideband modulator to obtain an upper sideband sweep electromagnetic wave signal in the 12.5-18.4 GHz range. The other two paths are input to two IQ mixers as reference signals after passing through a sixth harmonic and a power amplifier, respectively.

[0017] Furthermore, the upper sideband signal is split into two paths by a power divider, and then multiplied by a six-fold frequency multiplier to a frequency range of 75-110.4 GHz, which serve as the transmission signals for paths O and X. The O and X mode transmission signals are split into two paths after passing through directional couplers. One path is input to the mixer as a reference signal, and the other path is input to the dual-polarized antenna as a detection signal. The O mode transmission signal is input to the H plane of the OMT in the dual-polarized antenna, and the X mode transmission signal is input to the E plane of the OMT in the dual-polarized antenna. The detection signals of the two modes are coupled together through the OMT, and their vibration directions are perpendicular to each other. After being emitted into the plasma, they do not affect each other, so that the O mode and X mode can be measured simultaneously. After the dual-polarized antenna transmits the detection signal into the plasma, the signal undergoes total reflection at a specific density. The reflected signal is then received by the dual-polarized antenna, amplified by a low-noise amplifier, and input into an isolator to ensure unidirectional signal transmission and prevent reverse signals from damaging microwave devices. After passing through the isolator, the reflected signal is input to the mixer, which down-converts the reference signal and the reflected signal to obtain the intermediate frequency signal. This intermediate frequency signal is input to the IQ mixer, and together with the frequency-multiplied 600 MHz crystal oscillator signal, it is demodulated by the IQ mixer to obtain the IQ two-channel signals. Finally, the IQ signals from both OX and OX modes are input into the acquisition card and converted into digital signals. Data processing is then performed to reconstruct the plasma density profile.

[0018] The beneficial effects of this invention are: This invention achieves a single-transmit, single-receive architecture by using a single dual-polarized antenna, coupling both O and X diagnostic modes, effectively enabling simultaneous measurement of both O and X diagnostic modes, resulting in high system integration and saving diagnostic window space.

[0019] This invention uses a 100MHz crystal oscillator and a single-sideband modulator to suppress image frequency and local oscillator leakage, thereby achieving a novel sweep frequency signal output with a clean spectrum, improving the system signal-to-noise ratio, and providing strong anti-interference capability.

[0020] This invention achieves accurate extraction of the phase of the reflected signal by using an IQ mixer to coherently demodulate the intermediate frequency signal. Based on this phase data, the system can effectively diagnose the radial velocity and direction of the plasma.

[0021] This invention provides a clock reference for the VCO, IQ mixer and data acquisition card by using a multi-output crystal oscillator, ensuring phase synchronization of the entire system and improving measurement accuracy and system stability.

[0022] This invention exhibits high spatiotemporal resolution. With a rapid frequency sweep of 20 μs, the system's temporal resolution reaches the order of 20 microseconds. Within a frequency sweep range of 75 GHz to 110 GHz (35 GHz bandwidth), the theoretical spatial resolution can reach approximately 4.2 mm, effectively resolving fine structures in plasma. Since the system's spatial resolution is proportional to the frequency sweep bandwidth, even higher spatial resolution can be achieved by extending the frequency band.

[0023] This invention employs a non-contact measurement method and an external antenna design, which avoids thermal damage to the diagnostic device caused by high internal heat load. The system has a high degree of integration and can operate reliably for a long time under extreme conditions. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the microwave reflectometer frame of the present invention.

[0025] Figure 2 This is an overall block diagram of the microwave reflectometer of the present invention.

[0026] Figure 3 This is a block diagram of the signal source unit of the present invention.

[0027] Figure 4 This is a block diagram of the transmitting unit of the present invention.

[0028] Figure 5 This is a block diagram of the transmission unit of the present invention.

[0029] Figure 6 This is a block diagram of the mixing unit of the present invention.

[0030] Figure 7 This is a block diagram of the signal processing unit of the present invention.

[0031] Figure 8 This is a flowchart of the method of the present invention. Detailed Implementation

[0032] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of this application with unnecessary detail.

[0033] It should be understood that, when used in this specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0034] It should also be understood that the terminology used in this application specification is for the purpose of describing particular embodiments only and is not intended to limit the application. As used in this application specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0035] The following is in conjunction with the appendix to this application specification. Figure 1-8 The technical solutions in the embodiments of this application are clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0037] Implementation Method 1 This embodiment provides a W-band microwave reflectometer for a high-heat-load plasma superconducting linear apparatus. This invention serves the experimental platform of the high-heat-load plasma superconducting linear apparatus, aiming to perform non-contact, high spatiotemporal resolution, and synchronous measurement of plasma density profiles under experimental conditions of high heat flux, strong magnetic field, and long-term steady-state operation. Its operating band (W-band) can cover 0.7-1.5 × 10⁻⁶. 20 m -3 With its wide density range, accurate measurement of density profiles in high-density areas can be achieved. Simultaneously, by using the same architecture, the frequency range can be extended to enable complete measurement of density profiles in both low-density and central high-density areas.

[0038] This invention designs a single-transmitter, single-receiver microwave reflectometer system for simultaneous O / X mode measurement to diagnose electron density in plasma under magnetic field conditions. The system utilizes a dual-polarized antenna to achieve strictly synchronized transmission and reception in O / X modes, and combines this with single-sideband modulation technology to simultaneously and with high precision acquire plasma electron density profiles, radial velocity, and their directions. This provides a novel microwave reflectometer scheme for studying the equilibrium, stability, and turbulence of magnetized plasmas.

[0039] like Figure 1 As shown, the system mainly includes a signal generation unit, a transmission unit, a transmission unit, a signal processing unit, and a mixing unit. The signal generation unit is connected to the transmission unit and the mixing unit respectively. The mixing unit is also connected to the signal processing unit, the transmission unit, the acquisition card, and the computer respectively. The transmission unit is also connected to the transmission unit, the signal processing unit, and the plasma respectively.

[0040] 1. Signal source unit, used to generate transmission signals, including crystal oscillator module and VCO module.

[0041] The crystal oscillator module, including a crystal oscillator and a frequency multiplier, is used to output the crystal oscillator signal; the VCO module, including a signal generator and a voltage-controlled oscillator, is used to generate the transmission signal.

[0042] A crystal oscillator is used to output a 100 MHz crystal signal, which is then divided into four paths: one crystal signal is output to the intermediate frequency port of the single-sideband modulator; one is output to the external reference clock input of the data acquisition card for synchronous frequency sweep timing; the other two crystal signals are multiplied by a sixth frequency multiplier to generate a 600 MHz signal, which is output to the mixer unit as the reference signal for the IQ mixer. A frequency multiplier is used to multiply the output crystal oscillator signal to 600 MHz to obtain the crystal oscillator signal; A signal generator is used to generate sawtooth wave signals to drive a voltage-controlled oscillator. The voltage-controlled oscillator generates a linear sweep frequency signal of 12.4-18.3GHz under the drive of the sawtooth wave signal and the synchronization of the crystal oscillator. The output terminal is connected to the local oscillator port of the single-sideband modulator. A single-sideband modulator is used to mix the signal generated by a voltage-controlled oscillator with the crystal oscillator signal to obtain a pure 12.5-18.4 GHz single-sideband signal.

[0043] 2. Transmitting unit, used to split the transmitted signal into two paths, one for O mode and the other for X mode, and multiply the frequencies to obtain the detection signal; The two-way power divider, with its input connected to the output of a single-sideband modulator, is used to divide the 12.5-18.4 GHz transmit signal of the signal source unit into two equal paths. A six-fold frequency multiplier is used to multiply the transmitted signal to 75-110.4 GHz, which are used as the transmitted signals for mode O and mode X, respectively.

[0044] 3. Transmission unit, which divides the transmitted signal into a reference signal and a detection signal, sends the detection signal to the plasma, and transmits the reflected signal reflected back from the plasma to the signal processing unit.

[0045] Directional coupler 1 is used to split the signal into two paths. The main output of directional coupler 1 outputs a probe signal to directional coupler 2, and the other coupling end outputs a reference signal to the mixer unit.

[0046] Directional coupler 2: The detection signal is input from the coupling end and output from the input end to the dual-polarized antenna; the reflected signal is input from the dual-polarized antenna to the input end and output from the output end to the signal processing unit. A dual-polarized antenna is used to couple the O and X modes, transmitting the detection signal into the plasma and receiving the reflected signal.

[0047] 4. Signal processing unit, used to amplify the reflected signal and ensure unidirectional signal transmission.

[0048] A low-noise amplifier is used to amplify the received reflected signal and optimize system noise. An isolator is used to ensure unidirectional transmission of reflected signals and prevent interference signals such as local oscillator leakage from subsequent mixers from being reflected back to the previous stage and damaging the low-noise amplifier.

[0049] 5. Mixing unit, used to perform a first mixing of the reflected signal and the reference signal to obtain the intermediate frequency signal, and to perform a second mixing of the intermediate frequency signal and the crystal oscillator reference signal to obtain the I and Q signals. An amplifier is used to amplify the power of the crystal oscillator signal to drive an IQ mixer; The mixer is used to down-convert the reflected signal and the reference signal to obtain the intermediate frequency signal. The reflected signal after passing through the isolator is input to the RF port of the mixer, and the reference signal from the directional coupler 1 is input to the local oscillator port of the mixer. The IQ mixer is used to mix the intermediate frequency signal output by the mixer with the crystal oscillator reference signal to obtain I and Q signals. The intermediate frequency signal of the mixer is input to the intermediate frequency port, the 600 MHz reference signal from the crystal oscillator is input to the local oscillator port, and the two output I and Q signals are input to the acquisition card for synchronous digitization.

[0050] The 100 MHz crystal oscillator is connected to hexadecimal multiplier I, hexadecimal multiplier II, and single-sideband modulator, respectively. The single-sideband modulator is also connected to voltage-controlled oscillator (VCO) and power divider, respectively. The VCO is connected to a signal generator. The power divider is connected to hexadecimal multiplier III and hexadecimal multiplier IV, respectively. Hexadecimal multiplier III is connected to directional coupler I-1. Hexadecimal multiplier IV is connected to directional coupler I-2. Directional coupler I-1 is connected to directional coupler II-1. Directional coupler I-2 is connected to directional coupler II-2. The sixth frequency multiplier I is connected to amplifier I, amplifier I is connected to IQ mixer I, and IQ mixer I is connected to mixer I and the acquisition card respectively; mixer I is connected to directional coupler I-1 and isolator I respectively, isolator I is connected to low noise amplifier I, low noise amplifier I is connected to directional coupler II-1, and directional coupler II-1 is connected to dual-polarized antenna; The sixth frequency multiplier II is connected to amplifier II, amplifier II is connected to IQ mixer II, IQ mixer II is connected to mixer II and acquisition card respectively; mixer II is connected to directional coupler I-2 and isolator II respectively, isolator II is connected to low noise amplifier II, low noise amplifier II is connected to directional coupler II-2, and directional coupler II-2 is connected to dual-polarized antenna.

[0051] This system operates in the W-band (75-110GHz). For diagnostic needs in other density ranges, the same solution can be used in different bands. By selecting components suitable for different frequency bands, a single-transmitter, single-receiver microwave reflectometer that can simultaneously measure O and X modes in different frequency bands can be built without changing the core method of this invention. The specific implementation is as follows: 1. Diagnostic testing for extremely low density bands such as the Ku band (12-18GHz): Directly use a Ku band VCO or select a 6-9GHz VCO with a frequency doubler, and adjust the operating frequency band of the SSB modulator and frequency doubler accordingly. During transmission, select appropriate operating frequency band components such as coaxial cables, directional couplers, low-noise amplifiers, and dual-polarized antennas.

[0052] 2. Low-density diagnostics in the Q-band (33-50GHz): A 16.5-25GHz VCO with a frequency doubler is selected, and the operating frequency bands of the SSB modulator and frequency doubler are adjusted accordingly. During transmission, coaxial cables, directional couplers, low-noise amplifiers, and dual-polarized antennas with appropriate operating frequencies are used.

[0053] 3. High-density diagnostics in the terahertz band: A scheme using a terahertz microwave source and a terahertz frequency multiplier is selected, along with components such as directional couplers, low-noise amplifiers, and dual-polarized antennas operating in the terahertz band. Typically, waveguides are required for transmission in high-frequency bands above the W band.

[0054] In summary, by selecting devices operating in different frequency bands, this invention can achieve flexible coverage from the Ku to W bands and even the terahertz band under the current technology of component suppliers, meeting the full-range density profile diagnostic requirements for high-density plasmas in the core, from cryogenic plasmas to tokamak fusion. This scalability further illustrates the broad applicability and enormous application potential of the architecture proposed in this invention.

[0055] Based on the HIT-PSI steady-state high heat load plasma experimental platform, this microwave reflectometer can be used for: 1. Plasma beam characteristic diagnosis: Real-time measurement of the spatiotemporal evolution of plasma density profile under steady-state operation to study beam uniformity and stability.

[0056] 2. Electromagnetic wave research under strong magnetic fields: Using synchronously acquired O / X mode data, we study the influence of a 2T strong magnetic field on the cutoff layer in electromagnetic wave propagation, and verify and improve the density inversion algorithm in magnetized plasma.

[0057] 3. Integration and Validation of Multiple Diagnostic Methods: Provide density benchmarks for other diagnostic methods such as probes and spectrometers on the platform, realize joint analysis and cross-validation of multiple diagnostic methods, and improve the reliability of the diagnostic system.

[0058] 4. Provide diagnostic support for simulating future fusion reactor divertor-related experiments: Provide accurate plasma density boundary conditions for experiments on the interaction between high heat flux plasma and target materials, and support research on heat flux and particle flow deposition mechanisms.

[0059] The microwave reflectometer described in this invention, by being applied in different wavelength bands, can accurately diagnose plasma densities within different density ranges. Its applicable platforms are as follows: 1. Used for diagnosing plasma density profiles and fluctuations in magnetically confined nuclear fusion devices. Applied to tokamak (conventional tokamak, spherical tokamak, etc.), stellarator, reverse field pinch and other devices, it can realize real-time and accurate measurement of the electron density profile from the plasma core to the boundary, providing data support for plasma confinement research.

[0060] 2. Used for monitoring the uniformity and stability of process plasma in industrial processing equipment. It is mainly applied to semiconductor manufacturing equipment (plasma etching machine, chemical vapor deposition equipment, etc.) and material surface treatment equipment. It can realize non-invasive, online monitoring of the spatial distribution uniformity and temporal evolution of plasma density in the reaction chamber, and realize closed-loop control of the process.

[0061] 3. Used to measure the density distribution and oscillation characteristics of plasma thruster plumes, applied in electric propulsion systems such as Hall effect thrusters and ion thrusters, as well as their ground testing and space experimental platforms. By diagnosing the plasma distribution at the thruster exit, it evaluates propulsion efficiency and beam characteristics, and is used to study plasma oscillations and uncertainties, providing data support for thruster design and optimization.

[0062] 4. Used in various basic plasma research devices such as linear plasma devices, Q devices, and magnetic mirror devices, to study fundamental plasma problems such as wave-particle interactions and turbulent transport by measuring density perturbations excited by Alfvén waves, ion acoustic waves, or various instabilities.

[0063] Implementation Method 2 This embodiment provides a measurement method for a W-band microwave reflectometer used in a high-heat-load plasma superconducting linear device, such as... Figure 8 As shown, the measurement method uses a W-band microwave reflectometer for a high-heat-load plasma superconducting linear apparatus as described in Embodiment 1. The measurement method is as follows: First, a signal generator outputs a sawtooth wave to control a voltage-controlled oscillator (VCO) to continuously sweep frequencies within the 12.4-18.3 GHz range with a period of 20 μs. A 100 MHz crystal oscillator emits a signal, which is split into three paths. One path, along with the VCO sweep signal, is input to a single-sideband modulator to obtain the upper sideband 12.5-18.4 GHz sweep electromagnetic wave signal. The other two paths are respectively passed through a sixth harmonic and a power amplifier before being input to two IQ mixers as reference signals.

[0064] The signal above is split into two paths by a power divider, and then multiplied by a six-fold frequency multiplier to a frequency range of 75-110.4GHz, which are used as the transmission signals for paths O and X.

[0065] The O and X mode transmission signals are split into two paths after passing through directional couplers. One path is input to the mixer as a reference signal, and the other path is input to the dual-polarized antenna as a probe signal. The O mode transmission signal is input to the H-plane of the OMT in the dual-polarized antenna, and the X mode transmission signal is input to the E-plane of the OMT in the dual-polarized antenna. The probe signals of the two modes are coupled together through the OMT, with their vibration directions perpendicular to each other. After being emitted into the plasma, they do not interfere with each other, enabling simultaneous measurement of O and X modes.

[0066] After the antenna transmits the detection signal into the plasma, the signal undergoes total reflection at a specific density. The reflected signal is then received by the dual-polarized antenna, amplified by a low-noise amplifier, and input into an isolator to ensure unidirectional signal transmission and prevent reverse signals from damaging microwave devices.

[0067] After passing through the isolator, the reflected signal is input to the mixer, which down-converts the reference signal and the reflected signal to obtain an intermediate frequency (IF) signal. This IF signal is then input to the IQ mixer, where it is demodulated along with the frequency-multiplied 600 MHz crystal oscillator signal to obtain two separate IQ signals.

[0068] Finally, the IQ signals from both OX and OX modes are input into the acquisition card and converted into digital signals. Data processing is then performed to reconstruct the plasma density profile.

[0069] The specific density location is specifically... Based on the microwave cutoff reflection effect, the relationship between the cutoff frequency and density in O-mode is:

[0070] The relationship between the cutoff frequency and density in X-mode is:

[0071] Where f_pe is the plasma frequency and f_ce is the electron cyclotron frequency. .

Claims

1. A W-band microwave reflectometer for a high-heat-load plasma superconducting linear apparatus, characterized in that, The W-band microwave reflectometer includes a signal generation unit, a transmission unit, a signal processing unit, and a mixing unit; The signal source unit is used to generate the transmitted signal; The transmitting unit is used to split the transmitted signal into two paths, one for O mode and the other for X mode, and multiply the two paths to obtain the detection signal. The transmission unit is used to divide the transmitted signal into a reference signal and a detection signal, send the detection signal to the plasma, and transmit the reflected signal reflected back from the plasma to the signal processing unit. The signal processing unit is used to amplify the reflected signal and ensure unidirectional signal transmission; The mixing unit is used to perform a first mixing of the reflected signal and the reference signal to obtain an intermediate frequency signal, and to perform a second mixing of the intermediate frequency signal and the crystal oscillator reference signal to obtain I and Q signals.

2. The W-band microwave reflectometer according to claim 1, characterized in that, The signal generating unit is connected to the transmitting unit and the mixing unit respectively. The mixing unit is also connected to the signal processing unit, the transmission unit, the acquisition card and the computer respectively. The transmission unit is also connected to the transmitting unit, the signal processing unit and the plasma respectively.

3. The W-band microwave reflectometer according to claim 1, characterized in that, The signal source unit includes a crystal oscillator module and a VCO module; the crystal oscillator module is used to output a crystal oscillator signal; the VCO module is used to generate a transmission signal. The crystal oscillator module includes a crystal oscillator and a frequency multiplier. The crystal oscillator outputs a 100 MHz crystal signal and divides the crystal signal into four paths: one crystal signal is output to the intermediate frequency port of the single-sideband modulator; one is output to the external reference clock input of the data acquisition card for synchronous frequency sweep timing; the other two crystal signals are multiplied by a sixth frequency multiplier to generate a 600 MHz signal, which is output to the mixing unit as the reference signal for the IQ mixer. The frequency multiplier is used to multiply the output crystal oscillator signal to 600 MHz to obtain the crystal oscillator signal; The VCO module includes a signal generator and a voltage-controlled oscillator (VCO); the signal generator is used to generate a sawtooth wave signal to drive the VCO. The voltage-controlled oscillator generates a linear sweep frequency signal of 12.4-18.3 GHz under the drive of the sawtooth wave signal and the synchronization of the crystal oscillator, and the output terminal is connected to the local oscillator port of the single sideband modulator. The signal generated by the voltage-controlled oscillator and the crystal oscillator signal are mixed by a single-sideband modulator to obtain a pure 12.5-18.4 GHz single-sideband signal.

4. The W-band microwave reflectometer according to claim 3, characterized in that, The transmitting unit includes a power divider and a frequency multiplier; the power divider is used to divide the 12.5-18.4 GHz transmitted signal of the signal source unit into two equal paths. The frequency multiplier is used to multiply the transmitted signal to 75-110.4 GHz, which are used as the transmitted signals for mode O and mode X, respectively.

5. The W-band microwave reflectometer according to claim 1, characterized in that, The transmission unit includes a directional coupler I, a directional coupler II, and a dual-polarized antenna; the directional coupler I is used to split the signal into two paths, with the main output terminal of the directional coupler I outputting a detection signal to the directional coupler II, and the other coupling terminal outputting a reference signal to the mixing unit; The detection signal of the directional coupler II is input from the coupling end and output from the input end to the dual-polarized antenna. The reflected signal is input from the dual-polarized antenna to the input end and output from the output end to the signal processing unit.

6. The W-band microwave reflectometer according to claim 3, characterized in that, The mixing unit includes an amplifier, an IQ mixer, and a mixer; the amplifier is used to amplify the power of the crystal oscillator signal to drive the IQ mixer. The mixer is used to down-convert the reflected signal and the reference signal to obtain an intermediate frequency signal. The reflected signal after passing through the isolator is input to the RF port of the mixer, and the reference signal from the directional coupler 1 is input to the local oscillator port of the mixer. The IQ mixer is used to mix the intermediate frequency signal output by the mixer with the crystal oscillator reference signal to obtain I and Q signals. The intermediate frequency signal of the mixer is input to the intermediate frequency port, the 600 MHz reference signal from the crystal oscillator is input to the local oscillator port, and the output I and Q signals are input to the acquisition card for synchronous digitization.

7. The W-band microwave reflectometer according to claim 6, characterized in that, The 100 MHz crystal oscillator is connected to hexadecimal multiplier I, hexadecimal multiplier II, and single-sideband modulator, respectively. The single-sideband modulator is also connected to voltage-controlled oscillator (VCO) and power divider, respectively. The VCO is connected to a signal generator. The power divider is connected to hexadecimal multiplier III and hexadecimal multiplier IV, respectively. Hexadecimal multiplier III is connected to directional coupler I-1. Hexadecimal multiplier IV is connected to directional coupler I-2. Directional coupler I-1 is connected to directional coupler II-1. Directional coupler I-2 is connected to directional coupler II-2. The sixth frequency multiplier I is connected to amplifier I, amplifier I is connected to IQ mixer I, and IQ mixer I is connected to mixer I and the acquisition card respectively; mixer I is connected to directional coupler I-1 and isolator I respectively, isolator I is connected to low noise amplifier I, low noise amplifier I is connected to directional coupler II-1, and directional coupler II-1 is connected to dual-polarized antenna; The sixth frequency multiplier II is connected to amplifier II, amplifier II is connected to IQ mixer II, IQ mixer II is connected to mixer II and acquisition card respectively; mixer II is connected to directional coupler I-2 and isolator II respectively, isolator II is connected to low noise amplifier II, low noise amplifier II is connected to directional coupler II-2, and directional coupler II-2 is connected to dual-polarized antenna.

8. A measurement method for a W-band microwave reflectometer used in a high-heat-load plasma superconducting linear device, characterized in that, The measurement method uses a W-band microwave reflectometer for a high-heat-load plasma superconducting linear apparatus as described in any one of claims 1-7, and the measurement method specifically includes: The signal generator outputs a sawtooth wave, which, under the combined action of the sawtooth wave and the crystal oscillator, drives the voltage-controlled oscillator to generate a signal, resulting in an upper sideband swept electromagnetic wave signal and two reference signals. The swept-frequency electromagnetic wave signal is split into an input mixer as a reference signal and an input dual-polarized antenna detection signal after passing through a directional coupler. The dual-polarized antenna transmits the detection signal, which passes through the plasma, isolator, and mixer to obtain two signals, I and Q. These signals are then input into the acquisition card and converted into digital signals. Data processing is then performed to reconstruct the plasma density profile.

9. The measurement method according to claim 8, characterized in that, First, a signal generator is used to output a sawtooth wave, which controls a voltage-controlled oscillator (VCO) and a 100 MHz crystal oscillator to continuously sweep the frequency in the 12.4-18.3 GHz range with a period of 20 μs. The signal generated by the VCO and the 100 MHz crystal oscillator is split into three paths. One path is input into a single-sideband modulator along with the VCO sweep signal to obtain the upper sideband 12.5-18.4 GHz sweep electromagnetic wave signal. The other two paths are input into two IQ mixers as reference signals after passing through a sixth harmonic and a power amplifier, respectively.

10. The measurement method according to claim 9, characterized in that, The upper sideband signal is split into two paths by a power divider, and then multiplied by a six-fold frequency multiplier to a frequency range of 75-110.4 GHz, which serve as the transmission signals for paths O and X. The O and X mode transmission signals are split into two paths after passing through directional couplers. One path is input to the mixer as a reference signal, and the other path is input to the dual-polarized antenna as a detection signal. The O mode transmission signal is input to the H plane of the OMT in the dual-polarized antenna, and the X mode transmission signal is input to the E plane of the OMT in the dual-polarized antenna. The detection signals of the two modes are coupled together through the OMT, and their vibration directions are perpendicular to each other. After being emitted into the plasma, they do not affect each other, so that the O mode and X mode can be measured simultaneously. After the dual-polarized antenna transmits the detection signal into the plasma, the signal undergoes total reflection at a specific density. The reflected signal is then received by the dual-polarized antenna, amplified by a low-noise amplifier, and input into an isolator to ensure unidirectional signal transmission and prevent reverse signals from damaging microwave devices. After passing through the isolator, the reflected signal is input to the mixer, which down-converts the reference signal and the reflected signal to obtain the intermediate frequency signal. This intermediate frequency signal is input to the IQ mixer, and together with the frequency-multiplied 600 MHz crystal oscillator signal, it is demodulated by the IQ mixer to obtain the IQ two-channel signals. Finally, the IQ signals from both OX and OX modes are input into the acquisition card and converted into digital signals. Data processing is then performed to reconstruct the plasma density profile.

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