Microwave reflectometer system for polar rotation speed distribution measurement on KSPEX device
By designing a microwave reflectometer system for the KSPEX device, employing multi-stage mixing and I/Q quadrature demodulation, the problems of complexity and poor frequency adaptability of existing systems were solved. This enabled high-precision measurement of plasma poloidal rotation velocity and diagnosis of density fluctuations, improving detection sensitivity and calibration capabilities.
Patent Information
- Application Number
- CN202511823191.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-05
- Publication Date
- 2026-03-06
AI Technical Summary
Existing microwave reflector systems are complex in structure, have high frequency bands, and are costly, making them difficult to apply to small and medium-sized space plasma simulation devices. Furthermore, traditional reflectors can only measure density profiles and cannot measure plasma poloidal rotation speed with high precision.
A microwave reflectometer system for the KSPEX device was designed, including a microwave signal source, a local oscillator signal source, a mixer, a signal processing module, a transmission module, and an acquisition module. It adopts a 1-10 GHz superheterodyne receiver and I/Q quadrature demodulation architecture, and achieves high-precision measurement of plasma poloidal rotation velocity through multi-stage mixing and signal processing.
It achieves high-precision measurement of plasma poloidal rotation velocity, provides a diagnostic method with high spatiotemporal resolution, enhances the detection sensitivity and linearity of frequency shift signals, supports cross-validation with traditional equipment, and provides experimental basis for absolute calibration.
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Figure CN121613129A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of microwave reflection system technology, and more particularly to a microwave reflector system for measuring the poloidal rotational velocity distribution on the KSPEX device. Background Technology
[0002] In magnetic confinement nuclear fusion and space plasma research, plasma density fluctuations and rotational velocity are key parameters for understanding turbulent transport and stability mechanisms. Traditional electrostatic probes suffer from problems such as plasma contamination and short lifespan. In contrast, microwave reflectometers, as a non-invasive microwave diagnostic tool, can invert the poloidal rotational velocity and density fluctuation wavenumber spectrum of plasma by measuring the Doppler frequency shift of the scattered echo in the plasma. They have advantages such as high spatiotemporal resolution and strong wavenumber selectivity, and have been widely used in fusion devices such as tokamaks.
[0003] Existing systems are mostly designed for large-scale fusion devices, resulting in complex structures, high frequencies, and high costs, making them difficult to directly apply to small and medium-sized space plasma simulation devices. Therefore, there is an urgent need for a high-performance microwave reflector system that is compact, operates in a suitable frequency band, and is easy to integrate. Summary of the Invention
[0004] Based on the technical problems existing in the background technology, the present invention proposes a microwave reflector system for measuring the poloidal rotational velocity distribution on the KSPEX device, which solves the problems of system complexity and poor frequency adaptability in the prior art, and realizes high-precision measurement of plasma poloidal rotational velocity.
[0005] This invention proposes a microwave reflectometer system for measuring the poloidal rotational velocity distribution on a KSPEX device, comprising:
[0006] A microwave signal source is used to output detection signals;
[0007] Local oscillator signal source, used to output local oscillation signal;
[0008] The first mixer is used for the first-stage mixing of the probe signal and the local oscillator signal;
[0009] The signal processing module is used to convert the frequency band of the mixed detection signal and local oscillation signal to the target transmission frequency band;
[0010] The transmission module is used for transmitting the target's radio frequency band and the scattered echo signal;
[0011] The second mixer is used for two-stage mixing of the scattered echo signal and the local oscillator signal;
[0012] The third mixer is used for the third-stage mixing of the probe signal and the output signal of the second mixer.
[0013] The acquisition module is used to acquire the signal output from the third mixer and calculate the plasma poloidal rotational velocity profile.
[0014] Preferably, the microwave signal source is an Agilent N5171B with an output frequency range of 0.5-2.75 GHz.
[0015] Preferably, the signal processing module includes a first frequency multiplier, a first amplifier, a first filter, and a second frequency multiplier arranged sequentially along the signal transmission direction;
[0016] The first frequency multiplier is used to multiply the output signal of the first mixer to 0.5-5 GHz;
[0017] The first amplifier is used to compensate for the insertion loss caused by the frequency doubling link and the directional coupler;
[0018] The first filter is used to suppress the fundamental frequency, third and higher harmonics, and subharmonic components;
[0019] The second frequency multiplier is used to multiply the signal to the target transmission frequency band of 1-10 GHz.
[0020] Preferably, the transmission module includes a directional coupler and a dual-ridge horn antenna;
[0021] The directional coupler has an input end connected to the output of the signal processing module, a coupling end connected to the double-ridged horn antenna, an isolation end connected to the matching load, and a through end connected to the receiving link. It is used to feed the target transmitted signal to the double-ridged horn antenna and directionally couple the scattered echo to the subsequent superheterodyne receiving channel.
[0022] The double-ridged horn antenna is used to transmit microwave signals into the plasma and receive the scattered echoes.
[0023] Preferably, the directional coupler is a single directional coupler with an operating frequency of 0.8-10 GHz and a coupling degree of 10 dB.
[0024] Preferably, the dual-ridge horn antenna provides a gain of ≥10 dB in a wide frequency band of 1-18 GHz and is used for both transmission and reception.
[0025] Preferably, a frequency divider 8 is further provided between the transmission module and the second mixer.
[0026] Preferably, the acquisition module includes a second filter and a second amplifier connected to one output of the third mixer, a third filter and a third amplifier connected to the other output of the third mixer, and both outputs of the third mixer are connected to the input of the digitizer.
[0027] This invention proposes a method for measuring the poloidal rotational velocity distribution on a KSPEX device, employing the aforementioned microwave reflectometer system. The method steps are as follows:
[0028] The detection signal is output through a microwave signal source;
[0029] The local oscillation signal is output through the local oscillator signal source;
[0030] The probe signal and the local oscillator signal are mixed in the first stage using the first mixer;
[0031] The signal processing module converts the frequency band of the primary mixing of the detection signal and the local oscillation signal to the target transmission frequency band.
[0032] The target's transmitting frequency band and scattered echo signal are transmitted through the transmission module;
[0033] The scattered echo signal and the local oscillator signal are mixed in two stages using a second mixer.
[0034] The detection signal is mixed with the output signal after two-stage mixing by the third mixer in a third stage;
[0035] The output signal of the third mixer is acquired by the acquisition module, and the plasma poloidal rotational velocity profile is calculated.
[0036] Beneficial technical effects of the present invention:
[0037] (1) This invention, through its integrated design with the KSPEX space plasma experimental device, can directly diagnose the fluctuations in plasma poloidal rotation speed and density, providing key physical information for understanding the interaction between space plasma turbulence and poloidal electric field, thereby helping laboratory plasma research to better grasp the mechanisms of ionospheric depletion and boundary layer evolution.
[0038] (2) The system of the present invention adds the high spatiotemporal resolution microwave diagnostic means of the KSPEX device, which can be cross-verified with traditional equipment such as electrostatic probes and spectrometers to achieve higher precision plasma rotation speed and fluctuation intensity measurement results.
[0039] (3) The present invention adopts a 1-10 GHz superheterodyne receiver and I / Q quadrature demodulation architecture, which realizes the amplitude-phase synchronous extraction of Doppler frequency shift from the hardware level, solves the limitation of traditional reflectometers that can only measure density profile, and significantly improves the detection sensitivity and linearity of frequency shift signal.
[0040] (4) The present invention provides a traceable experimental basis for implementing absolute calibration in vacuum plasma by simulating the scatterer platform by reciprocating iron plate. Attached Figure Description
[0041] Figure 1 This is a schematic diagram of the microwave reflector system proposed in this invention;
[0042] Figure 2 The microwave reflector system proposed in this invention is shown in the following figures: (a) the relationship between output power and input frequency, and (b) the ray tracing results of incident wave frequencies of 2, 4, and 5 GHz at the same incident angle under an input power of 1-10 GHz.
[0043] Figure 3 The following are the timing diagrams of (a) I and Q signals, (b) I / Q phase detector output signal diagram, and (c) power spectrum of complex signal of microwave reflector on KSPEX device under the Doppler frequency shift test proposed in this invention.
[0044] In the diagram: 1-Microwave signal source, 2-First mixer, 3-First frequency multiplier, 4-First amplifier, 5-First filter, 6-Second frequency multiplier, 7-Directional coupler, 8-Frequency divider, 9-Local oscillator signal source, 10-Second mixer, 11-Third mixer, 12-Second filter, 13-Third filter, 14-Second amplifier, 15-Third amplifier, 16-Digitizer. Detailed Implementation
[0045] The present invention will be further explained below with reference to specific embodiments.
[0046] Example 1
[0047] Reference Figure 1 The present invention proposes a microwave reflectometer system for measuring the poloidal rotational velocity distribution on a KSPEX device, comprising: a microwave signal source 1, a local oscillator signal source 9, a signal processing module, a transmission module, a mixing module, and an acquisition module.
[0048] Microwave signal source 1 is used to generate detection signals. In this embodiment, microwave signal source 1 is an Agilent N5171B with an output frequency range of 0.5-2.75 GHz.
[0049] Local oscillator signal source 9 is used to provide a local oscillation signal with an output frequency of 3 GHz as a mixing reference. It works in conjunction with the microwave signal source to convert high-frequency signals into intermediate-frequency signals through a superheterodyne structure.
[0050] The signal processing module is used to convert the signal frequency to the target frequency band. Through a two-stage low-noise frequency doubling link, and with the help of bandpass filtering and gain compensation technology, the low-power intermediate frequency obtained after mixing is cleanly and stably converted to the 1-10GHz target transmission frequency band.
[0051] In this embodiment, the signal processing module includes a first frequency multiplier 3, a first amplifier 4, a first filter 5, and a second frequency multiplier 6 arranged sequentially along the signal transmission direction. The first frequency multiplier 3 is used to multiply the output signal of the first mixer 2 to 0.5-5 GHz; the first amplifier 4 is a 1-12 GHz low-noise amplifier used to compensate for the insertion loss caused by the frequency multiplication link and the directional coupler, and can provide 17 dB gain, 1.5 dB noise figure, and +19 dBm output power with only +5V / 55 mA power supply; the first filter 5 is used to suppress the fundamental frequency, third and higher harmonics, and subharmonic components, ensuring that only the required second-order frequency multiplication energy is retained to enter the second frequency multiplier, thereby purifying the spectrum and reducing system spuriouss; the second frequency multiplier 6 is used to multiply the signal to the target transmission frequency band of 1-10 GHz.
[0052] The transmission module is used to inject the detection signal, which has been purified and amplified by the frequency multiplier module, into the plasma cutoff layer with extremely low sidelobes and horizontal tilt. It also simultaneously collects the weak backscattered echoes carrying Doppler frequency shift information on the same beam path, so as to realize efficient bidirectional transmission of electromagnetic waves with single-antenna multiplexing, high spatial resolution and high signal-to-noise ratio.
[0053] A frequency divider is also provided between the transmission module and the second mixer 10. The frequency divider adopts a four-way frequency division.
[0054] In this embodiment, the transmission module includes a double-ridged horn antenna and a directional coupler. The directional coupler is a single directional coupler with an operating frequency of 0.8-10 GHz and a coupling degree of 10 dB. Its input end is connected to the output of the signal processing module, its coupling end is connected to the double-ridged horn antenna, its isolation end is connected to a matched load, and its through end is connected to the receiving link. It is used to feed the target transmitted signal to the double-ridged horn antenna and directionally couple the scattered echo to the subsequent superheterodyne receiving channel. The double-ridged horn antenna is used to transmit microwave signals to the plasma and receive the scattered echo. The double-ridged horn antenna provides a gain of ≥10 dB in a wide frequency band of 1-18 GHz and is used for both transmission and reception, ensuring that the KSPEX microwave reflector can still obtain sufficient echo power and beam pointing stability under the asymmetric layout outside the vacuum chamber.
[0055] The mixing module mainly includes a first mixer 2, a second mixer 10, and a third mixer 11. The first mixer 2 performs a first-stage mixing of the probe signal and the local oscillator signal to generate an intermediate frequency (IF) signal. The second mixer 10 performs a second-stage mixing of the scattered echo signal (after frequency division by four) with the local oscillator signal. The third mixer 11 performs a third-stage mixing of the probe signal with the output signal from the second-stage mixing of the second mixer 10. The third mixer 11 uses an I / Q mixer to output in-phase I-channel and quadrature Q-channel baseband signals.
[0056] The acquisition module is used to acquire the I and Q signals output by the third mixer 11. It performs point-by-point differential and smooth fitting on the continuous phase sequence using the phase partial derivative method to extract the Doppler frequency shift. Combined with the scattering wavenumber given by ray tracing, the plasma poloidal rotation velocity profile is calculated.
[0057] In this embodiment, the acquisition module includes a second filter 12 and a second amplifier 14 connected to one output of the third mixer 11, and a third filter 13 and a third amplifier 15 connected to the other output of the third mixer 11. Both outputs of the third mixer 11 are connected to the input of the digitizer 16. The digitizer 16 is used to convert I / Q signals into digital quantities in real time and without loss, and to accurately record the quadrature waveforms of the I / Q signals. The digitizer 16 supports remote control.
[0058] Among them, the phase partial derivative method calculates the Doppler frequency shift using the following formula:
[0059]
[0060]
[0061] In the formula, This represents the Doppler frequency shift. Where φ is the phase of the I and Q signals, derived from... Sure.
[0062] Ray tracing is used to simulate the propagation path of microwaves in plasma, calculate the cutoff layer location and the vertical wavenumber at the cutoff layer, and is implemented based on the WKB approximation method.
[0063] Example 2
[0064] This invention proposes a method for measuring the poloidal rotational velocity distribution on a KSPEX device, using the microwave reflectometer system described in Example 1. The method steps are as follows:
[0065] The system outputs a detection signal via microwave signal source 1; outputs a local oscillation signal via local oscillator signal source 9; performs a first-stage mixing of the detection signal and the local oscillation signal via first mixer 2; converts the frequency band of the first-stage mixing of the detection signal and the local oscillation signal to the target transmission frequency band via signal processing module; transmits the target transmission frequency band and the scattered echo signal via transmission module; performs a second-stage mixing of the scattered echo signal and the local oscillation signal via second mixer 10; performs a third-stage mixing of the detection signal and the output signal of the second-stage mixing via third mixer 11; and acquires the output signal of the third mixer 11 via acquisition module and calculates the plasma poloidal rotation velocity profile.
[0066] To test the performance of the microwave reflector device, such as Figure 2As shown in section (a), the microwave reflector system described in this embodiment of the invention has an average output power of approximately 7.05 dRm at an input power of 1-10 GHz, which preliminarily demonstrates the stability of the microwave reflector system. Figure 2 As shown in part (b), the ray tracing results indicate that, under typical plasma density distributions, the cutoff layer location that can be measured by the microwave reflectometer system on the KSPEX device can cover the entire small radius.
[0067] In the tabletop test, a metal plate that moves back and forth perpendicular to the propagation direction is used to simulate plasma scattering, such as... Figure 3 As shown in part (a), the curves in the figure are the timing diagrams of the I / Q signals measured by the system. It can be seen that as the speed of the iron plate gradually increases, the waveform amplitude and period of the I and Q channels gradually decrease over time, indicating that the Doppler frequency shift increases. Based on the timing period calculation, the frequency of one-quarter of the Doppler frequency shift is approximately 46.4 Hz. Figure 3 As shown in part (b), the output signal diagram of the I / Q phase detector is shown. The phase detector output forms a symmetrical phase trajectory on the IQ plane, and the system has good balance and symmetry. Figure 3 Part (c) shows the power spectrum of the complex signal of the microwave reflector. A clear Doppler frequency shift can be seen in the figure. The frequency of one-quarter of the Doppler frequency shift is about 48.8 Hz, which is in good agreement with the period calculation results above, thus proving that the system is operating normally.
[0068] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application. The scope of this application is defined by the appended claims and their equivalents, all of which should be included within the protection scope of this application.
Claims
1. A microwave reflectometer system for poloidal rotation velocity profile measurements on a KSPEX device, characterized by, The application relates to a microwave signal source (1) for outputting a detection signal, a local signal source (9) for outputting a local oscillation signal, a first mixer (2) for first-order mixing of the detection signal and the local oscillation signal, a signal processing module for converting a frequency band after mixing of the detection signal and the local oscillation signal into a target transmission frequency band, a transmission module for transmission of the target transmission frequency band and a scattered echo signal, a second mixer (10) for second-order mixing of the scattered echo signal and the local oscillation signal, a third mixer (11) for third-order mixing of the detection signal and a second-order mixing output signal of the second mixer (10), and a collection module for collecting a signal output by the third mixer (11) and calculating a plasma rotational velocity profile. The microwave signal source (1) is an Agilent N5171B, and the output frequency range is 0.5-2.75 GHz. The signal processing module comprises a first frequency multiplier (3), a first amplifier (4), a first filter (5) and a second frequency multiplier (6) arranged in sequence along a signal transmission direction. The first frequency multiplier (3) is used for frequency multiplication of an output signal of the first mixer (2) to 0.5-5 GHz. The first amplifier (4) is used for compensating insertion loss caused by a frequency multiplication link and a directional coupler. The first filter (5) is used for suppressing fundamental wave, third-order and above harmonic wave and subharmonic wave components. The second frequency multiplier (6) is used for frequency multiplication of the signal to a target transmission frequency band of 1-10 GHz. The transmission module comprises a directional coupler (7) and a double-ridge horn antenna. The directional coupler is connected with the signal processing module output at an input end, connected with the double-ridge horn antenna at a coupling end, connected with a matching load at an isolation end, connected with a receiving link at a straight-through end, used for feeding the target transmission signal to the double-ridge horn antenna and coupling the scattered echo to a subsequent superheterodyne receiving channel.
2. The microwave reflectometer system for polar-rotating velocity profile measurements on a KSPEX device of claim 1, wherein, The double-ridge horn antenna is used for transmitting the microwave signal to the plasma and receiving the scattered echo.
3. The microwave reflectometer system for polar-rotating velocity profile measurements on a KSPEX device of claim 1, wherein, The directional coupler is a single directional coupler with a working frequency of 0.8-10 GHz and a coupling degree of 10 dB. The double-ridge horn antenna provides a gain of greater than 10 dB in a wide frequency band of 1-18 GHz, and simultaneously transmits and receives. A frequency divider (8) is further arranged between the transmission module and the second mixer (10). The collection module comprises a second filter (12) and a second amplifier (14) connected with one output of the third mixer (11), a third filter (13) and a third amplifier (15) connected with another output of the third mixer (11), and both outputs of the third mixer (11) are connected with an input end of a digitizer (16). The method comprises the following steps:
4. The microwave reflectometer system for polar-rotating velocity profile measurements on a KSPEX device of claim 1, wherein, The microwave signal source (1) is used for outputting a detection signal; The local signal source (9) is used for outputting a local oscillation signal; The first mixer (2) is used for first-order mixing of the detection signal and the local oscillation signal; 5. The microwave reflectometer system for polar-rotating velocity profile measurements on a KSPEX device of claim 4, wherein, The signal processing module is used for converting a frequency band after first-order mixing of the detection signal and the local oscillation signal into a target transmission frequency band; 6. The microwave reflectometer system for polar-rotating velocity profile measurements on a KSPEX device of claim 4, wherein, The transmission module is used for transmission of the target transmission frequency band and a scattered echo signal; 7. The microwave reflectometer system for polar-rotating velocity profile measurements on a KSPEX device of claim 1, wherein, 8. The microwave reflectometer system for polar-rotating velocity profile measurements on a KSPEX device of claim 1, wherein, 9. A method for polar rotation velocity profile measurement on a KSPEX device using the microwave reflectometer system of any one of claims 1-8, characterized in that, The scattered echo signal and the local oscillation signal are secondly mixed by a second mixer (10); The output signal of the second mixer (10) after the second mixing is thirdly mixed with a detection signal by a third mixer (11); The output signal of the third mixer (11) is collected by a collection module, and the plasma polar rotation speed profile is calculated.