System and method for real-time detection of plasma microwave frequency and power

Abstract

This invention discloses a system and method for real-time detection of microwave frequency and power in plasma, belonging to the field of magnetic confinement fusion plasma heating and diagnostic technology. It extracts the main microwave signal output from the gyrotron via a waveguide coupler, and after passing through an attenuator and a millimeter-wave mixer, splits it into two paths: one path is sent to a power detection module to obtain power information, and the other path is sent to a phase-locked loop frequency tracking module to obtain frequency information, achieving synchronous real-time detection of frequency and power. This invention has advantages such as fast response speed, high measurement accuracy, and strong anti-interference capability. It is suitable for online monitoring of the gyrotron microwave source in tokamak devices such as EAST, providing reliable data support for plasma heating and control, and ensuring the safe and stable operation of the device.

Description

Technical Field

[0001] This invention belongs to the field of magnetic confinement fusion plasma heating and diagnostic technology, specifically relating to a system and method for real-time detection of plasma microwave frequency and power. Background Technology

[0002] Magnetic confinement fusion devices (such as tokamaks and stellarators) aim to achieve safe, clean, and sustainable energy output through controlled nuclear fusion reactions in high-temperature plasmas, representing a crucial pathway to addressing future human energy needs. Electron cyclotron resonance (ECRH) heating, a key auxiliary heating method in this field, is widely used in core physical processes such as plasma initiation, heating, current-driven processes, confinement mode modulation, and fracture mitigation. The cyclotron tube is the core microwave source of the ECRH system, and its output microwave frequency and power directly determine the energy deposition location, heating efficiency, and plasma confinement quality. As fusion devices evolve towards long-pulse, steady-state operation (such as ITER and CFETR), the monitoring requirements for ECRH systems have evolved from simple offline calibration to real-time online monitoring with millisecond-level response, high precision, and resistance to strong electromagnetic interference.

[0003] Currently, real-time detection of microwave power output from a gyrotron primarily employs the directional coupler detection method. This method extracts coupled power by placing a directional coupler in the transmission line to estimate the main power. This method boasts a fast response speed and has been applied in the ECRH system of a commercial fusion device. However, existing directional couplers are mostly optimized for a single operating frequency. When the gyrotron needs to switch between multiple frequencies or perform frequency sweeps, the change in coupling degree with frequency introduces significant measurement errors, affecting the accuracy and reliability of power detection. Another power measurement method—liquid calorimetry—while highly accurate, is essentially a time-delay measurement. It can only obtain the accumulated heat and average power after the discharge ends, failing to reflect the dynamic changes in microwave power in real time during gyrotron operation. Furthermore, it is susceptible to environmental vibrations and heat source interference, making it difficult to meet the millisecond-level real-time power monitoring requirements during long-pulse operation.

[0004] In frequency detection, the output microwave frequency (millimeter wave and even terahertz band) of a gyrotron is mainly measured using the heterodyne method, which combines a spectrum analyzer and a spread spectrum module. This method down-converts the high-frequency signal to the intermediate frequency range through external harmonic mixing, and then obtains the frequency information through a fast Fourier transform. It offers high measurement accuracy, but relies heavily on the frequency scanning of the spectrum analyzer, resulting in response times typically on the order of seconds or even longer. It is primarily used for factory testing, debugging, and offline diagnostics of gyrotrons. For frequency drift caused by factors such as cavity thermal expansion and electron beam parameter fluctuations during long-pulse operation, offline frequency measurement cannot capture it in real time, making it difficult to promptly assess and adjust the gyrotron's operating status.

[0005] It is worth noting that the output frequency and power of a gyrotron are not independent but rather have a complex coupling relationship. Adjustments to parameters such as operating voltage, magnetic field strength, and cathode temperature simultaneously affect both frequency and power. However, existing frequency and power measurement methods are separate in terms of response speed, measurement principles, and system structure, and an integrated detection scheme capable of synchronously and in real-time acquiring both parameters has not yet been formed. This separation results in a lack of real-time, coordinated parameter support for comprehensive diagnosis of the gyrotron's operating status, hindering the refined control of the ECRH system and the optimization of fusion experiments.

[0006] In summary, existing methods for detecting the output microwave frequency and power of gyrotrons have the following main problems and drawbacks:

[0007] Power detection: Liquid calorimetry has a time delay and cannot achieve millisecond-level real-time dynamic monitoring; directional coupler detection method has reduced measurement accuracy due to changes in coupling degree under multi-frequency conditions, and its anti-electromagnetic interference capability is insufficient.

[0008] Frequency detection: The heterodyne method based on spectrum analyzers has a long response time (on the order of seconds), which cannot meet the requirements of real-time monitoring of frequency drift in fusion experiments, and can only be used for offline diagnosis.

[0009] Separate detection methods: The frequency and power detection systems are independent of each other, lacking integrated, synchronous, and real-time parameter acquisition capabilities, making it difficult to support comprehensive evaluation and closed-loop control of the ECRH system output status under long pulse and steady-state operation.

[0010] Therefore, there is an urgent need to develop a system and method that can synchronously and in real time detect the microwave frequency and power output of a gyrotron, and that has millisecond-level response, high precision, multi-frequency adaptability and strong electromagnetic interference resistance. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention provides a system and method for real-time detection of plasma microwave frequency and power. This system is applicable to the real-time detection of microwave frequency and power output from gyrotrons in magnetic confinement fusion devices such as tokamaks and stellarators, and is also applicable to real-time detection of microwave frequency and power in other applications.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A system for real-time detection of plasma microwave frequency and power, enabling synchronous millisecond-level real-time detection of frequency and power, includes a waveguide coupling aperture, a 60 dB attenuator, a heterodyne receiver module, a phase-locked loop frequency tracking module, and a power detection module.

[0014] The waveguide coupling aperture is set on the output transmission waveguide of the cyclotron heating system, and the output end of the waveguide coupling aperture is connected to the input end of the heterodyne receiving module through a 60 dB attenuator.

[0015] The heterodyne receiver module includes a tuned local oscillator and a millimeter-wave mixer. The input of the millimeter-wave mixer is connected to the output of a 60dB attenuator. The millimeter-wave mixer is connected to the local oscillator. The output of the millimeter-wave mixer serves as the output of the heterodyne receiver module.

[0016] The input terminal of the phase-locked loop frequency tracking module is connected to the output terminal of the heterodyne receiver module, and is used to track the intermediate frequency signal output by the heterodyne receiver module and output the instantaneous frequency signal.

[0017] The input terminal of the power detection module is connected to the output terminal of the heterodyne receiver module, and is used to detect the power of the intermediate frequency signal output by the heterodyne receiver module and output the instantaneous power signal.

[0018] The present invention also provides a method for real-time detection of plasma microwave frequency and power, which, using the above-described system for real-time detection of plasma microwave frequency and power, includes the following steps:

[0019] Step 1: Extract a portion of the cyclotron heating signal from the main waveguide with a minimum coupling efficiency of less than 30 dB using a waveguide coupler installed on the output transmission waveguide of the cyclotron heating system. After passing through a 60 dB attenuator, the signal is input to the heterodyne receiving module.

[0020] Step 2: Use the local oscillator and millimeter-wave mixer in the heterodyne receiver module to perform down-conversion processing on the extracted signal to obtain an intermediate frequency signal that retains the original frequency drift information and relative power information;

[0021] Step 3: The intermediate frequency signal is sent to the phase-locked loop frequency tracking module, which consists of a phase-locked mixer, a low-pass filter, and a voltage-controlled oscillator, to obtain the instantaneous frequency signal. At the same time, it is sent to the power detection module to obtain the instantaneous power signal. The phase-locked loop frequency tracking module and the power detection module process in parallel to achieve synchronous detection.

[0022] Step 4: Synchronously package the obtained instantaneous frequency signal and instantaneous power signal, and send them to the plasma control system or data acquisition system in real time through a high-speed digital interface.

[0023] Beneficial effects:

[0024] 1. This invention integrates a pinhole coupling, heterodyne downconversion, and intermediate frequency parallel processing architecture, achieving for the first time in the field of cyclotron heating detection in magnetic confinement fusion devices, synchronous millisecond-level real-time detection of frequency and power. Frequency is tracked by a phase-locked loop, and power is measured by an intermediate frequency detector; the two operate independently and in parallel, completely solving the problems of separate frequency and power measurements and slow response speeds (typically hundreds of milliseconds to seconds) in traditional methods. This allows both frequency and power detection response times to reach the millisecond level.

[0025] 2. By downconverting high-frequency signals of hundreds of GHz to intermediate-frequency signals in the hundreds of MHz range, this invention effectively avoids the extremely high cost and complex design required for high-speed analog-to-digital conversion in the millimeter-wave or submillimeter-wave bands. It significantly reduces the engineering difficulty of direct sampling in the high-frequency band, making the phase-locked loop tracking and detector scheme easy to implement and stable in practical engineering.

[0026] 3. Since the intermediate frequency (IF) is far from the main electromagnetic interference (EMI) band during tokamak operation (such as magnetic disturbances and radio frequency heating spurious radiation from tens of kHz to tens of MHz), combined with IF bandpass filtering and shielding design, this invention can significantly improve the signal-to-noise ratio and reliability of the detection system. Furthermore, the pinhole coupling method is passive coupling and does not introduce additional interference, thus possessing strong resistance to strong EMI. In frequency detection, the phase-locked loop (PLL) can achieve extremely low frequency tracking error within its operating bandwidth, typically better than 0.1% relative error, and can continuously track frequency variations caused by gyrotron operating point drift, avoiding measurement blind spots and time gaps in traditional spectrum analyzer scanning modes. It offers high frequency detection accuracy and continuous drift tracking. In power detection, a logarithmic detector with high linearity and wide dynamic range can be selected for power detection in the IF band. Compared to direct detection at the main waveguide or millimeter-wave coupling end, it has a larger dynamic range and is less susceptible to interference from high-power echoes from the main path, resulting in a wide dynamic range and good linearity in power detection.

[0027] 4. The instantaneous frequency and instantaneous power output by this invention can be either analog voltage signals or digital signals after analog-to-digital conversion, output through high-speed digital interfaces such as optical fiber, PCIe (high-speed peripheral component interconnection) or EtherCAT (Ethernet control automation technology). The response delay can be controlled within 1 to 2 milliseconds, making it easy to integrate with plasma control systems and meeting the real-time requirements of future fusion devices for rapid feedback control of cyclotron heating.

[0028] 5. By changing the local oscillator frequency and the center frequency of the intermediate frequency filter, this invention can be adapted to cyclotron heating systems in different frequency bands, such as 28GHz, 105GHz, 140GHz, 170GHz and even above 200GHz. Furthermore, the probe or pinhole coupling structure can be flexibly designed according to the waveguide type, making it suitable for various magnetic confinement fusion devices and exhibiting good versatility and scalability. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a system for real-time detection of plasma microwave frequency and power according to the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] like Figure 1 As shown, this invention provides a system for real-time detection of plasma microwave frequency and power, including a waveguide coupling aperture, a 60 dB attenuator, a heterodyne receiving module, a phase-locked loop (PLL) frequency tracking module, and a power detection module. The waveguide coupling aperture is disposed on the output transmission waveguide of the cyclotron heating system. The output end of the waveguide coupling aperture is connected to the input end of the heterodyne receiving module via the 60 dB attenuator. The input end of the millimeter-wave mixer of the heterodyne receiving module is connected to the output end of the 60 dB attenuator. The millimeter-wave mixer is connected to a local oscillator source, and its output serves as the output end of the heterodyne receiving module. The input end of the PLL frequency tracking module is connected to the output end of the heterodyne receiving module, used for frequency tracking of the intermediate frequency (IF) signal output by the heterodyne receiving module and outputting an instantaneous frequency signal. The input end of the power detection module is connected to the output end of the heterodyne receiving module, used for power detection of the IF signal output by the heterodyne receiving module and outputting an instantaneous power signal.

[0032] Preferably, the waveguide coupling aperture, the 60 dB attenuator, and the heterodyne receiver module are connected by a WR-10 waveguide, and an RF coaxial cable is used to output the signal to the phase-locked loop frequency tracking module and the power detection module.

[0033] The heterodyne receiver module includes a low-noise amplifier (...). Figure 1 (not shown in the image), tunable local oscillator, millimeter-wave mixer and intermediate frequency filter ( Figure 1 (Not shown in the image) The local oscillator and the millimeter-wave mixer are connected by an RF coaxial cable.

[0034] The waveguide coupling aperture is a small-aperture coupling structure with a coupling efficiency of less than 30 dB (one-thousandth). A 60 dB attenuator then reduces the signal power coupled from the megawatt-level main waveguide power to the system used for real-time plasma microwave frequency and power detection to the milliwatt level. Without affecting the main transmission, a portion of the cyclotron heating signal is extracted from the main waveguide with minimal coupling, thus reducing the signal power entering the system for real-time plasma microwave frequency and power detection to a safe milliwatt level while avoiding impact on the megawatt-level main power transmission.

[0035] By setting the local oscillator frequency of the local oscillator source so that the difference between the input RF signal and the fixed local oscillator frequency falls into the intermediate frequency (IF) band, and after mixing by a millimeter-wave mixer and filtering by an IF filter, a clean IF signal is obtained. Figure 1 The intermediate frequency signal is the mixed output signal; this intermediate frequency signal completely preserves the frequency drift information and relative power information of the original cyclone heating signal.

[0036] The intermediate frequency (IF) signal is split into two paths by a broadband power divider. The first IF signal is sent to the frequency detection branch of the phase-locked loop (PLL) frequency tracking module, and the second IF signal is sent to the power detection branch of the power detection module. The two branches are processed in parallel to achieve synchronous millisecond-level detection of frequency and power.

[0037] The frequency detection branch consists of a phase-locked mixer, a low-pass filter, and a voltage-controlled oscillator (VCO) connected in sequence, forming a closed-loop frequency tracking circuit. The input of the phase-locked mixer serves as the input of the PLL frequency tracking module and is connected to the input of the low-pass filter. The output of the low-pass filter is connected to the input of the VCO. The high-frequency output of the VCO is connected to the phase-locked mixer to form a closed loop. Using an intermediate frequency (IF) signal as a reference signal for locking, the PLL frequency tracking module has a loop bandwidth on the order of kHz, enabling a frequency detection response time on the order of milliseconds. By measuring the control voltage of the VCO in real time and combining it with the division ratio of the PLL frequency tracking module and the local oscillator frequency setpoint, the instantaneous frequency of the original gyroradiometer signal is calculated using the formula fRF(t) = fLO ± fIF(t). This allows for continuous real-time tracking of the frequency drift of the gyroradiometer caused by changes in operating conditions. Here, fRF represents the gyroradiometer frequency, fLO represents the local oscillator frequency, fIF represents the output frequency of the phase-locked mixer, and t represents time.

[0038] The power detection branch includes a detector and a bias adjustment circuit connected in sequence. The detector can be a high-speed detector diode or a logarithmic detector. The second intermediate frequency signal is input to the detector, which, together with the analog-to-digital converter and the bias adjustment circuit, has the advantages of fast response speed, good linearity and high temperature stability due to the intermediate frequency being much lower than the original millimeter wave band. Its response time can reach the microsecond level. With appropriate filtering, it can reliably achieve millisecond-level power detection response. The instantaneous output power of the gyrothering heating system is calculated in real time by using the pre-calibrated system transmission coefficient between the main waveguide power and the intermediate frequency detector voltage.

[0039] The present invention also provides a method for real-time detection of plasma microwave frequency and power, comprising the following steps:

[0040] Step 1: Set a small-aperture coupling structure as a waveguide coupler at the 90-degree adapter of the output transmission waveguide of the cyclotron heating system. Extract part of the cyclotron heating signal from the main waveguide with extremely low coupling (usually coupling efficiency less than 30 dB). Then, through a 60 dB attenuator, reduce the signal power entering the system used for real-time detection of plasma microwave frequency and power to a safe range of milliwatts while avoiding affecting the transmission of megawatt-level main power. The safe range is that the input power should be between -30 dBm and 0 dBm.

[0041] Step 2: Input the coupled microwave signal into the heterodyne receiver module. By setting the local oscillator frequency, the difference between the input RF signal and the fixed local oscillator falls into the intermediate frequency band. After mixing and filtering, a pure intermediate frequency signal is obtained. This intermediate frequency signal completely preserves the frequency drift information and relative power information of the original cyclotron heating signal.

[0042] Step 3: The intermediate frequency signal obtained above is divided into two paths by a broadband power divider. The first intermediate frequency signal is sent to the frequency detection branch of the phase-locked loop frequency tracking module, and the second intermediate frequency signal is sent to the power detection branch of the power detection module. The two branches are processed in parallel to achieve synchronous millisecond-level detection of frequency and power.

[0043] In the frequency detection branch, the intermediate frequency signal is used as the reference signal for locking. The phase-locked loop frequency tracking module has a loop bandwidth on the order of kHz, which enables the frequency detection response time to reach the order of milliseconds. By measuring the voltage in real time to control the oscillator's control voltage and combining the frequency division ratio of the phase-locked loop frequency tracking module with the local oscillator frequency setting value, the instantaneous frequency of the original gyro heating signal is obtained by back-calculation according to the formula fRF(t)=fLO±fIF(t), thereby realizing continuous real-time tracking of the frequency drift of the gyro heating tube caused by changes in operating conditions.

[0044] In the power detection branch, the second intermediate frequency signal is connected to the detector, which, together with the analog-to-digital converter and bias adjustment circuit, has advantages such as fast response speed, good linearity and high temperature stability due to the intermediate frequency being much lower than the original millimeter wave band. Its response time can reach the microsecond level. With appropriate filtering, it can reliably achieve millisecond-level power detection response. The instantaneous output power of the gyrothering heating system is calculated in real time by using the pre-calibrated system transmission coefficient between the main waveguide power and the intermediate frequency detection voltage.

[0045] Step 4: Synchronously package the obtained instantaneous frequency and instantaneous output power, and send them in real time to the plasma control system or data acquisition system through a high-speed digital interface for closed-loop control and physical analysis of the cyclotron heating system.

[0046] Preferably, a switchable attenuator or limiter is set at the front end of the heterodyne receiver module to protect the subsequent circuits from transient high-power impacts caused by cyclotron heating arcing or reflection; a digital auxiliary algorithm is introduced in the phase-locked loop frequency tracking module to improve the initial locking speed over a wide frequency range; and a temperature compensation circuit is used in the power detection module to eliminate the drift effect of ambient temperature changes on the detector sensitivity.

[0047] Preferably, the instantaneous frequency and instantaneous output power are synchronously packaged and sent to the plasma control system or data acquisition system in real time through a high-speed digital interface. The total delay can be controlled within 1 to 2 milliseconds to meet the closed-loop control requirements and is used for closed-loop control and physical analysis of the cyclotron heating system.

[0048] Preferably, by changing the local oscillator frequency and the center frequency of the intermediate frequency filter, it can be adapted to gyrotrons in the 28 GHz, 105 GHz, 140 GHz, 170 GHz and even higher frequency bands, thus having good versatility.

[0049] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A system for real-time detection of plasma microwave frequency and power, characterized in that, To achieve real-time, millisecond-level synchronization of frequency and power, the system includes a waveguide coupling aperture, a 60 dB attenuator, a heterodyne receiver module, a phase-locked loop frequency tracking module, and a power detection module. The waveguide coupling aperture is set on the output transmission waveguide of the gyrothermal heating system, and the output end of the waveguide coupling aperture is connected to the input end of the heterodyne receiver module through a 60dB attenuator. The heterodyne receiver module includes a tunable local oscillator and a millimeter-wave mixer. The input of the millimeter-wave mixer is connected to the output of a 60 dB attenuator. The millimeter-wave mixer is connected to the local oscillator. The output of the millimeter-wave mixer serves as the output of the heterodyne receiver module. The input terminal of the phase-locked loop frequency tracking module is connected to the output terminal of the heterodyne receiver module, and is used to track the intermediate frequency signal output by the heterodyne receiver module and output the instantaneous frequency signal. The input terminal of the power detection module is connected to the output terminal of the heterodyne receiver module, and is used to detect the power of the intermediate frequency signal output by the heterodyne receiver module and output the instantaneous power signal.

2. The system for real-time detection of plasma microwave frequency and power according to claim 1, characterized in that, The waveguide coupling aperture is connected to a 60 dB attenuator and a heterodyne receiver module via a WR-10 waveguide.

3. The system for real-time detection of plasma microwave frequency and power according to claim 2, characterized in that, The phase-locked loop frequency tracking module includes a phase-locked mixer, a low-pass filter, and a voltage-controlled oscillator. The input terminal of the phase-locked mixer serves as the input terminal of the phase-locked loop frequency tracking module and is connected to the input terminal of the low-pass filter. The output of the low-pass filter is connected to the input of the voltage-controlled oscillator. The high-frequency output of the voltage-controlled oscillator is connected to the phase-locked mixer to form a closed loop.

4. The system for real-time detection of plasma microwave frequency and power according to claim 3, characterized in that, The control voltage of the voltage-controlled oscillator is used as the output of the phase-locked loop frequency tracking module to output the instantaneous frequency signal.

5. A system for real-time detection of plasma microwave frequency and power according to claim 1, characterized in that, It also includes a high-speed digital interface. The input of the high-speed digital interface is connected to the output of the phase-locked loop frequency tracking module and the output of the power detection module, respectively. The output of the high-speed digital interface is used to connect to the receiving port of the plasma control system or data acquisition system.

6. A method for real-time detection of plasma microwave frequency and power, employing the system for real-time detection of plasma microwave frequency and power according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Extract a portion of the cyclotron heating signal from the main waveguide with a minimum coupling efficiency of less than 30dB using a waveguide coupler installed on the output transmission waveguide of the cyclotron heating system. After passing through a 60dB attenuator, the signal is input to the heterodyne receiving module. Step 2: Use the local oscillator and millimeter-wave mixer in the heterodyne receiver module to perform down-conversion processing on the extracted signal to obtain an intermediate frequency signal that retains the original frequency drift information and relative power information; Step 3: The intermediate frequency signal is sent to the phase-locked loop frequency tracking module, which consists of a phase-locked mixer, a low-pass filter, and a voltage-controlled oscillator, to obtain the instantaneous frequency signal. At the same time, it is sent to the power detection module to obtain the instantaneous power signal. The phase-locked loop frequency tracking module and the power detection module process in parallel to achieve synchronous detection. Step 4: Synchronously package the obtained instantaneous frequency signal and instantaneous power signal, and send them to the plasma control system or data acquisition system in real time through a high-speed digital interface.

7. The method according to claim 6, characterized in that, In step 1, the waveguide coupler is a small-aperture coupling structure, and the coupling degree is changed by adjusting the size and position of the aperture.

8. The method according to claim 6, characterized in that, In step 2, the intermediate frequency signal is filtered by an intermediate frequency filter.

9. The method according to claim 8, characterized in that, In step 3, the instantaneous frequency signal of the original cyclotron heating signal is obtained by measuring the control voltage of the voltage-controlled oscillator in real time and combining the frequency division ratio of the phase-locked loop frequency tracking module with the local oscillator frequency setting value.

10. The method according to claim 6, characterized in that, In step 3, the instantaneous power signal of the gyrothering system is calculated in real time using the pre-calibrated system transmission coefficient between the main waveguide power and the intermediate frequency detector voltage.

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