A magnetic field helicity angle distribution measurement system based on an electron cyclotron emission radiometer

Abstract

The present invention belongs to the technical field of tokamaks, and particularly relates to a magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer. The present invention includes a polarizer, a servo motor, a microwave antenna, a band-stop filter, a high-pass filter, a low-noise RF amplifier, a directional coupler, an RF mixer, a directional coupler, a Gunn oscillator, a band-pass filter, an intermediate-frequency amplifier, a power divider, an intermediate-frequency band-pass filter, an intermediate-frequency amplifier, an intermediate-frequency mixer, an intermediate-frequency Gunn oscillator, an adjustable attenuator, a band-pass filter, a detector, a low-pass filter, a video amplifier, and a data collector. The present invention changes the intensity of the received ECE through a controllable polarizer, and obtains the spatio-temporal distribution of the magnetic field helical angle by finding the angle of the polarizer at the maximum intensity point.

Description

Technical Field

[0001] The present invention belongs to the technical field of tokamaks, and particularly relates to a magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer. Background Art

[0002] In a tokamak plasma, the total magnetic field formed by the superposition of the toroidal magnetic field and the poloidal magnetic field generated by the current has a certain helical angle relative to the equatorial plane. The magnitude of the helical angle directly determines the distribution of the safety factor q, which is crucial for research on plasma equilibrium, plasma control, disruption prediction, magnetohydrodynamic instability, micro-turbulence instability, high-energy particles, etc. In recent years, in order to achieve a high confinement operation mode of the plasma, many advanced tokamak operation schemes have been proposed, requiring the plasma magnetic shear s to be in a weak shear or even negative shear state, etc. These advanced operation modes are inseparable from the accurate measurement of the magnetic field helical angle.

[0003] Currently, the diagnosis of the magnetic field helical angle distribution in the world mainly includes the Motional Stark Effect (MSE) diagnosis and the Faraday rotation effect diagnosis. These two methods obtain the magnetic field helical angle information by measuring the spectral line broadening and the rotation angle. The Motional Stark polarization diagnosis is an active diagnosis method that relies on neutral beam injection. The direction of the magnetic field is obtained by measuring the polarization direction of a certain series of spectra of neutral beam particles. Since the MSE spectral line is very complex, the spectral resolution ability is very poor at low magnetic fields. Various broadening mechanisms lead to spectral line overlap, and the instability of the beam energy leads to a decrease in the signal-to-noise ratio. Therefore, the MSE polarization diagnosis is a diagnosis that is internationally recognized as very difficult. The Faraday rotation effect is generally measured by a polarization interferometer system. Since the incident wave vector k frequency is much higher than the characteristic absorption and reflection frequencies in the tokamak plasma, and the velocities of the left-handed circularly polarized light and the right-handed circularly polarized light in the magnetized plasma are different, the component of the poloidal magnetic field in the direction parallel to the wave vector k will cause the polarization direction of the wave vector k to deflect. The deflection angle is related to the electron density of the path and the parallel component of the poloidal magnetic field. Since the Faraday deflection angle is the result of a chord integral, the distribution of the electron density and the magnetic field needs to be introduced, so a large error will be introduced. The systems for diagnosing these two magnetic field helical angles are both relatively complex, have a large volume, are expensive, and are difficult to maintain. Summary of the Invention

[0004] The technical problem solved by the present invention is to propose a magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer for the complex, large-volume, expensive, and difficult-to-maintain Motional Stark polarimeter and polarization interference diagnostic system. The intensity of the received ECE is changed by a controllable polarizer, and the spatio-temporal distribution of the magnetic field helical angle is obtained by finding the angle of the polarizer at the maximum intensity.

[0005] The technical solution adopted by the present invention:

[0006] A magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer, comprising a polarizer, a servo motor, a microwave antenna, a band-stop filter, a high-pass filter, a low-noise RF amplifier, a directional coupler, an RF mixer, a directional coupler, a Gunn oscillator, a band-pass filter, an intermediate-frequency amplifier, a power divider, an intermediate-frequency band-pass filter, an intermediate-frequency amplifier, an intermediate-frequency mixer, an intermediate-frequency Gunn oscillator, an adjustable attenuator, a band-pass filter, a detector, a low-pass filter, a video amplifier, and a data collector. The polarizer is connected to the servo motor, and the servo motor is connected to the data collector. The polarizer faces the plasma directly. The microwave antenna is placed directly behind the polarizer to receive signals passing through the polarizer from the plasma. The rear end of the microwave antenna is connected to the band-stop filter to filter out the frequency band of electron cyclotron heating. The rear end of the band-stop filter is connected to the high-pass filter to filter out the image frequency signal of the ECE RF, with a low-frequency attenuation greater than 30 dB. The signal passing through the high-pass filter is connected to the low-noise RF amplifier to improve the signal-to-noise ratio. The signal passing through the low-noise RF amplifier is connected to the directional coupler to prevent the reflected standing wave from damaging the low-noise amplifier. The microwave signal is input into the RF end of the RF mixer through the directional coupler. The local oscillator end of the RF mixer is sequentially connected to the directional coupler and the Gunn oscillator. The RF and local oscillator signals of the RF mixer are mixed to generate an intermediate-frequency signal, which is connected to the band-pass filter to filter out the stray signals outside the working frequency band. The intermediate-frequency signal is filtered and then passed through the intermediate-frequency amplifier and then into the power divider to send the intermediate-frequency signal into the intermediate-frequency channel. The broadband intermediate-frequency signal is filtered to the working intermediate-frequency band through the intermediate-frequency band-pass filter. The narrowband intermediate-frequency signal passing through the intermediate-frequency band-pass filter is connected to the intermediate-frequency amplifier to improve the signal-to-noise ratio of the intermediate-frequency signal, and then passed into the intermediate-frequency mixer. The local oscillator end of the intermediate-frequency mixer is connected to the intermediate-frequency Gunn oscillator corresponding to the working frequency. The second-stage intermediate-frequency signal generated by the mixing is connected to the adjustable attenuator to adjust the strength of the signal. The second-stage intermediate-frequency signal is passed through the band-pass filter to adjust the measurement ability of the ECE system for signal perturbation and filter out the low-frequency interference signals. Finally, the signal enters the detector to measure the signal strength. The detected signal is connected to the low-pass filter to filter out the high-frequency interference signals. The low-pass filtered signal is connected to the video amplifier to increase the signal amplitude and finally connected to the data collector.

[0007] The initial polarization direction of the polarizer is placed in the vertical polarization direction.

[0008] The rotation period of the servo motor is 10 milliseconds and it rotates at a constant speed, and the control signal is connected to the data collector to know the polarization direction of the polarizer in real time through the control signal.

[0009] The band-stop of the band-stop filter should be greater than 60 dB, so that the intensity of the microwave signal entering the low-noise RF amplifier is weaker than -10 dB.

[0010] The noise figure of the low-noise RF amplifier should be lower than 5 dB, and the amplification gain should be greater than 20 dB.

[0011] Suppress the signals outside the intermediate frequency operating band by more than 30 dB.

[0012] Select a bandpass frequency band from 30 MHz to 300 MHz to achieve a spatial resolution of 1 to 2 cm for the helical angle distribution measurement of the ECE-measured magnetic field.

[0013] Select a low-pass filter with a cutoff frequency of 300 kHz.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] (1) A magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer provided by the present invention utilizes the characteristic that the intensity of the second harmonic X-mode in the tokamak plasma is much greater than that of the second harmonic O-mode. A controllable polarizer is used to measure the ECE radiation intensity at different polarization angles, and the magnetic field helical angle is obtained through half of the deflection angle corresponding to the maximum signal.

[0016] (2) A magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer provided by the present invention. In the tokamak discharge experiment, as the servo motor drives the polarizer to rotate, the ECE signal will show a sinusoidal periodic change. The helical angle of the magnetic field line can be calculated by recording the polarization angle corresponding to the last strongest point.

[0017] (3) A magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer provided by the present invention is not restricted by external conditions such as neutral beam injection. It can unrestrictedly obtain the distribution of the magnetic field helical angle in the tokamak plasma. The time resolution depends on the rotation speed of the servo motor and can reach within 10 microseconds. This diagnostic system can be obtained by modifying the ECE diagnostic system, with low cost, and is a very promising means for diagnosing the magnetic field helical angle distribution.

[0018] (4) A magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer provided by the present invention has a simple structure, small volume, low cost, and is convenient for maintenance. At the same time, it also has high spatio-temporal distribution capabilities, does not rely on external conditions such as neutral beam injection, and can provide real-time measurement of the magnetic field helical angle distribution in the tokamak plasma. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of a magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer provided by the present invention;

[0020] Figure 2 It is a schematic diagram for obtaining the maximum signal;

[0021] Figure 3Schematic diagram of the measurement result of the magnetic field helix angle distribution;

[0022] In the figure: 1 - polarizer, 2 - servo motor, 3 - microwave antenna, 4 - band-stop filter, 5 - high-pass filter, 6 - low-noise RF amplifier, 7 - directional coupler, 8 - RF mixer, 9 - directional coupler, 10 - Gunn oscillator, 11 - band-pass filter, 12 - intermediate-frequency amplifier, 13 - power divider, 14 - intermediate-frequency band-pass filter, 15 - intermediate-frequency amplifier, 16 - intermediate-frequency mixer, 17 - intermediate-frequency Gunn oscillator, 18 - adjustable attenuator, 19 - band-pass filter, 20 - detector, 21 - low-pass filter, 22 - video amplifier, 23 - data collector. Specific implementation manner

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0025] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0026] Such as Figure 1As shown in the figure, a magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer provided by the present invention includes a polarizer 1, a servo motor 2, a microwave antenna 3, a band-stop filter 4, a high-pass filter 5, a low-noise RF amplifier 6, a directional coupler 7, an RF mixer 8, a directional coupler 9, a Gunn oscillator 10, a band-pass filter 11, an intermediate-frequency amplifier 12, a power divider 13, an intermediate-frequency band-pass filter 14, an intermediate-frequency amplifier 15, an intermediate-frequency mixer 16, an intermediate-frequency Gunn oscillator 17, an adjustable attenuator 18, a band-pass filter 19, a detector 20, a low-pass filter 21, a video amplifier 22, and a data collector 23. The polarizer 1 is connected to the servo motor 2, and the servo motor 2 is connected to the data collector 23. The initial polarization direction of the polarizer 1 is placed in the vertical polarization direction and is facing the plasma 24. The rotation period of the servo motor 2 is a uniform rotation of 10 milliseconds, and the control signal is connected to the data collector 23. The polarization direction of the polarizer 23 can be known in real time through the control signal.

[0027] The microwave antenna 3 is placed directly behind the polarizer 1 to receive the signal from the plasma 24 passing through the polarizer 1. The rear end of the microwave antenna 3 is connected to the band-stop filter 4 to filter out the frequency band of electron cyclotron heating. It is required that the band-stop should be greater than 60 dB so that the intensity of the microwave signal entering the low-noise RF amplifier 6 is weaker than -10 dB. The rear end of the band-stop filter 4 is connected to the high-pass filter 5 to filter out the image frequency signal of the ECE RF. The low-frequency attenuation is greater than 30 dB. The rear end of the high-pass filter 5 is connected to the low-noise RF amplifier 6 to improve the signal-to-noise ratio of the signal. The noise figure of the low-noise RF amplifier 6 should be lower than 5 dB, and the amplification gain is greater than 20 dB. The signal passing through the low-noise RF amplifier 6 is connected to the directional coupler 7 to prevent the reflected standing wave from damaging the low-noise amplifier 6. The microwave signal is input to the RF end of the RF mixer 8 through the directional coupler 7. The local oscillator end of the RF mixer 8 is sequentially connected to the directional coupler 9 and the Gunn oscillator 10. In order to measure the magnetic field helical angle distribution, an appropriate operating frequency of the Gunn oscillator 10 should be selected so that the detection range of the ECE diagnosis covers the plasma core to the weak-field side edge of the plasma.

[0028] The radio frequency signal and the local oscillator signal are mixed by the radio frequency mixer 8 to generate an intermediate frequency signal, which is then connected to the band-pass filter 11 to filter out the spurious signals outside the working frequency band. After filtering, the intermediate frequency signal passes through the intermediate frequency amplifier 12 and then enters the power divider 13, which sends the intermediate frequency signal into the intermediate frequency channel. The broadband intermediate frequency signal is filtered by the intermediate frequency band-pass filter 14 to the working intermediate frequency band. To ensure the interpretability of the intermediate frequency signal, the signals outside the intermediate frequency working band need to be suppressed by more than 30 dB. The narrowband intermediate frequency signal passing through the intermediate frequency band-pass filter 14 is connected to the intermediate frequency amplifier 15 to improve the signal-to-noise ratio of the intermediate frequency signal, and then enters the intermediate frequency mixer 16. The local oscillator terminal of the intermediate frequency mixer 16 is connected to the intermediate frequency Gunn oscillator 17 corresponding to the working frequency. The generated second-stage intermediate frequency signal is connected to the adjustable attenuator 18 to adjust the signal strength. The second-stage intermediate frequency signal with appropriate signal strength enters the band-pass filter 19 to adjust the measurement ability of the ECE system for signal perturbation and filter out the low-frequency interference signals. Usually, a band-pass frequency band of 30 MHz to 300 MHz is selected to achieve a spatial resolution of 1 to 2 cm for measuring the magnetic field helical angle distribution by ECE. Finally, the signal enters the detector 20 to measure the signal strength. The detected signal is connected to the low-pass filter 21 to filter out the high-frequency interference signals. Generally, a low-pass filter of 300 kHz is selected. The low-pass filtered signal is connected to the video amplifier 22 to increase the signal amplitude and finally enters the data collector 23.

[0029] The control signal of the servo motor 2 connected to the data collector 23 and the data of the multi-channel ECE are analyzed to find the voltage signal value of the control signal of the servo motor 2 corresponding to the maximum signal strength of each ECE channel. Since the voltage signal value of the control signal corresponds one-to-one to the polarization angle of the polarizer 1, the polarization angle corresponding to the maximum amplitude of each channel in each servo motor cycle can be obtained.

[0030] Since the radiation intensity of the second harmonic X-mode is much greater than that of the second harmonic O-mode in the Tokamak plasma, we receive the ECE signal of the second harmonic X-mode, set the initial position of the polarizer and the antenna to the vertical polarization direction, and adjust the period of the microwave sweep source to be consistent with that of the servo motor. When there is no magnetic field helical angle caused by the plasma current, the polarized ECE diagnostic system obtains the maximum signal when the polarizer is vertically polarized. When the plasma current exists and causes a certain magnetic field helical angle, the polarized ECE diagnostic system obtains the maximum signal when the polarizer rotates a certain angle, as Figure 2 shown by the black hollow circles in. At this time, half of the angle between the polarization angle and the vertical direction is the magnetic field helical angle, as Figure 3 shown.

[0031] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, in any aspect, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

[0032] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A magnetic field helicity angle distribution measurement system based on an electron cyclotron emission radiometer, characterized in that, it includes a polarizer (1), a servo motor (2), a microwave antenna (3), a band-stop filter (4), a high-pass filter (5), a low-noise RF amplifier (6), a directional coupler (7), an RF mixer (8), a directional coupler (9), a Gunn oscillator (10), a band-pass filter (11), an intermediate-frequency amplifier (12), a power divider (13), an intermediate-frequency band-pass filter (14), an intermediate-frequency amplifier (15), an intermediate-frequency mixer (16), an intermediate-frequency Gunn oscillator (17), an adjustable attenuator (18), a band-pass filter (19), a detector (20), a low-pass filter (21), a video amplifier (22), and a data collector (23). The polarizer (1) is connected to the servo motor (2), the servo motor (2) is connected to the data collector (23), the polarizer (1) faces the plasma (24), the microwave antenna (3) is placed directly behind the polarizer (1) to receive the signal passing through the polarizer (1) from the plasma (24). The rear end of the microwave antenna (3) is connected to the band-stop filter (4) to filter out the frequency band of electron cyclotron heating. The rear end of the band-stop filter (4) is connected to the high-pass filter (5) to filter out the image frequency signal of the ECE RF, with a low-frequency attenuation greater than 30 dB. The rear end of the high-pass filter (5) is connected to the low-noise RF amplifier (6) to improve the signal-to-noise ratio of the signal. The signal passing through the low-noise RF amplifier (6) is connected to the directional coupler (7) to prevent the reflected standing wave from damaging the low-noise amplifier (6). The microwave signal is input into the RF port of the RF mixer (8) through the directional coupler (7). The local oscillator port of the RF mixer (8) is sequentially connected to the directional coupler (9) and the Gunn oscillator (10). The RF and local oscillator signals of the RF mixer (8) are mixed to generate an intermediate-frequency signal, which is connected to the band-pass filter (11) to filter out the stray signals outside the working frequency band. The intermediate-frequency signal is filtered and then passes through the intermediate-frequency amplifier (12) and then through the power divider (13) to send the intermediate-frequency signal into the intermediate-frequency channel. The broadband intermediate-frequency signal is filtered by the intermediate-frequency band-pass filter (14) to filter the broadband intermediate-frequency signal into the working intermediate-frequency band. The narrowband intermediate-frequency signal passing through the intermediate-frequency band-pass filter (14) is connected to the intermediate-frequency amplifier (15) to improve the signal-to-noise ratio of the intermediate-frequency signal, and then passes through the intermediate-frequency mixer (16). The local oscillator port of the intermediate-frequency mixer (16) is connected to the intermediate-frequency Gunn oscillator (17) corresponding to the working frequency. The second-stage intermediate-frequency signal generated by the mixing is connected to the adjustable attenuator (18) to adjust the strength of the signal. The second-stage intermediate-frequency signal passes through the band-pass filter (19) to adjust the measurement ability of the ECE system for signal perturbation and filter out the low-frequency interference signals. Finally, the signal enters the detector (20) to measure the signal intensity. The detected signal is connected to the low-pass filter (21) to filter out the high-frequency interference signals. The low-pass filtered signal is connected to the video amplifier (22) to increase the signal amplitude and finally connected to the data collector (23).

2. The magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer according to claim 1, wherein, the initial polarization direction of the polarizer (1) is placed in the vertical polarization direction.

3. The magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer according to claim 1, wherein, the rotation period of the servo motor (2) is a uniform rotation of 10 milliseconds and the control signal is connected to the data collector (23), and the polarization direction of the polarizer (23) is known in real time through the control signal.

4. The magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer according to claim 1, wherein, the band rejection of the band-stop filter (4) should be greater than 60 dB, so that the microwave signal intensity entering the low-noise RF amplifier (6) is weaker than -10 dB.

5. The magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer according to claim 1, wherein, the noise figure of the low-noise RF amplifier (6) should be lower than 5 dB and the amplification gain is greater than 20 dB.

6. The magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer according to claim 1, wherein, the signal outside the intermediate frequency operating band is suppressed by more than 30 dB.

7. The magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer according to claim 1, wherein, a band-pass frequency band of 30 MHz to 300 MHz is selected, so that the spatial resolution of the ECE measurement of the magnetic field helical angle distribution reaches 1 to 2 centimeters.

8. The magnetic field helical angle distribution measurement system based on an electron cyclotron emission radiometer according to claim 1, wherein, a low-pass filter of 300 kHz is selected.

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