CN110806510A

CN110806510A - System for measuring wave number in direction of 4.6GHz low-clutter parallel magnetic field

Info

Publication number: CN110806510A
Application number: CN201911066069.3A
Authority: CN
Inventors: 李妙辉; 王云飞; 丁伯江; 吴则革; 王茂; 刘亮; 赵连敏
Original assignee: Hefei Institutes of Physical Science of CAS
Current assignee: Hefei Institutes of Physical Science of CAS
Priority date: 2019-11-04
Filing date: 2019-11-04
Publication date: 2020-02-18
Anticipated expiration: 2039-11-04
Also published as: CN110806510B

Abstract

The invention discloses a system for measuring wave number in the direction of a 4.6GHz low-clutter parallel magnetic field, which is used for realizing phase measurement of high-frequency microwaves freely transmitted in Tokamak plasma and further analyzing and obtaining the wave number in the direction of the low-clutter parallel magnetic field. Including both the vacuum side and the atmospheric side. The vacuum side comprises a magnetic probe array, a high-temperature-resistant stable phase coaxial line and a coaxial feeder. The atmosphere side comprises a two-stage frequency reduction circuit and a high-speed data acquisition module. The low clutter is coupled by a magnetic probe array with a fixed distance, is transmitted out through a coaxial feed through, is mixed with a two-stage difference frequency circuit, then reduces the frequency of 4.6GHz high-frequency microwave to about 20MHz, is sent to a multi-channel synchronous acquisition module with the sampling rate as high as 100MS/s, and finally obtains the phase information of each channel through FFT data processing.

Description

System for measuring wave number in direction of 4.6GHz low-clutter parallel magnetic field

Technical Field

The invention belongs to the technical field of microwaves, and particularly relates to a system for measuring low clutter phases in a tokamak plasma.

Background

Low stray current drive (LHCD) is an important non-inductive current drive and heating means on tokamak devices. Most magnetic confinement nuclear fusion devices in the world have low-clutter systems, such as Tore-Supra in France, Alcator C-Mod in America, EAST tokamak in China, and the like. In the physical experiment of the low clutter, the parallel wave number k of the low clutter_//Is a key physical quantity that determines the propagation, absorption and current driving efficiency of the low noise waves in the plasma. Initial k before entering plasma_//The phase difference between adjacent waveguides of the low-noise antenna can be calculated through electromagnetic wave-plasma coupling software, but when the low-noise passes through a plasma scraping layer, the low-noise antenna is influenced by various nonlinear effects, so that the parallel wave number of the low-noise antenna can be changed, and the driving efficiency and the heating effect of the low-noise antenna can be influenced. In order to analyze the absorption and propagation of the low noise wave and the plasma of the scraped layer, the phase of the low noise wave needs to be measured to analyze and obtain the parallel wave number k_//And (4) information.

The microwave propagating in the regular waveguide can acquire phase information through the directional coupler, but the microwave freely propagates in the plasma, so that the traditional directional coupler is difficult to identify the phase information of the wave propagating in a specific direction, which is a difficulty in measuring the phase of the low-noise wave in the tokamak plasma.

Disclosure of Invention

The invention aims to provide a measuring system for a freely-propagated 4.6GHz high-power low-noise wave number in Tokamak plasma, so that key data support is provided for low-noise current driving and heating physical experiment analysis.

The invention provides a system for measuring wave number in the direction of a 4.6GHz low clutter parallel magnetic field, which comprises a magnetic probe array, a phase-stabilized coaxial line, a vacuum coaxial electrode, a two-stage frequency reduction circuit and a high-speed data acquisition module, wherein the magnetic probe array is connected with the vacuum coaxial electrode; low clutter signals in the plasma are coupled by a magnetic probe, transmitted to a vacuum flange by a high-temperature-resistant silicon dioxide stable phase coaxial line in a vacuum chamber, transmitted out of a Tokamak vacuum chamber through a vacuum coaxial electrode, transmitted to a difference frequency circuit by a common coaxial line, subjected to difference frequency with two-stage local oscillation, and finally collected by a multi-channel high-speed collection module;

the magnetic probe structure in the magnetic probe array is as follows: the outside of the magnetic probe coil is covered by a shielding barrel with a rectangular gap, the gap is arranged at the top cover of the shielding barrel, and the plane of the coil is strictly vertical to the rectangular gap; the two-stage difference frequency circuit reduces the frequency of 4.6GHz microwave to 20MHz without changing the phase information.

Further, the present invention provides a magnetic probe with a rectangular slit for coupling microwaves propagating in a specific direction, the probe being sensitive to microwaves propagating in only one direction; and simultaneously, a frequency reduction circuit is provided to reduce the high-frequency microwave coupled by the probe to about 20 MHz. The frequency reduction circuit is realized by two-stage frequency reduction, the amplitude and the phase of the output microwave signal only depend on the input RF signal and are irrelevant to the local oscillator signal, so the output of the frequency reduction circuit can accurately reflect the information of the measured RF signal. And finally, acquiring data and restoring the waveform by a high-speed acquisition system with the sampling rate more than 2 times of the microwave frequency.

The magnetic probe coil is formed by winding a silicon dioxide semi-rigid coaxial line inner conductor and is welded on an outer conductor, and the outside of the coil is covered by a stainless steel shielding barrel. The bottom cover of the stainless steel shielding barrel is provided with a rectangular gap, so that the magnetic probe can only be coupled with magnetic field disturbance parallel to the long edge direction. The low noise wave propagated in the plasma is slow wave, the magnetic field of the slow wave is perpendicular to the background confinement magnetic field, so that the magnetic probe with the long side of the rectangular crack perpendicular to the magnetic field is sensitive to the disturbance magnetic field (has a good shielding effect on microwaves in other directions), and the coupling of the low noise wave microwave characteristic is realized.

The two-stage frequency reduction circuit is composed of local oscillators of 4.9GHz and 280 MHz. The 4.6GHz low clutter signal coupled out by the array of magnetic probes is at first with the first level local oscillator 4.9GHz difference frequency, its output signal frequency is reduced to 300MHz, the signal is again with the second level local oscillator 280MHz difference frequency, so the original 4.6GHz radio frequency signal is reduced the frequency to 20 MHz. The output signal strength of the frequency reducing circuit is determined by the 4.6GHz radio frequency signal, and the phase information of the frequency reducing circuit is not changed.

The high-speed acquisition module is used for synchronous acquisition with 8-channel sampling rate up to 100 MS/s. The sampling rate of 100MS/s is sufficient to restore the waveform pattern of the 20MHz signal according to the nyquist's law, thereby obtaining its phase information through FFT data processing.

The invention has the advantages that the magnetic probe has good directivity in coupling characteristic, and is characterized in that: the outside of the magnetic probe coil is covered by a shielding barrel with a rectangular gap, and the plane of the coil is strictly vertical to the rectangular gap. Meanwhile, the frequency reduction method is adopted to reduce the frequency of 4.6GHz microwave to 20MHz, thereby meeting the acquisition capability of the existing acquisition card. The invention adopts two-stage frequency reduction, and the design of the circuit ensures that the phase information is not distorted, thereby realizing the measurement of the low clutter wave number.

Drawings

FIG. 1 is a schematic diagram of the main structure of the system of the present invention;

FIG. 2 is a schematic diagram of a two-stage difference frequency circuit;

FIG. 3 is a graph of the variation of the difference frequency circuit output voltage (circles) and phase (triangles) with RF power (test results);

FIG. 4 is a graph of the spectrum obtained by FFT analysis (CH1, CH2, … …. CH8 represents the signal of each of the 8 magnetic probes);

FIG. 5 shows the phase difference between adjacent channels obtained by FFT analysis (CH2-CH1 represents the phase difference between the 2 nd magnetic probe and the 1 st, CH3-CH2 represents the phase difference between the 3 rd magnetic probe and the 2 nd, and so on).

In the figure: the device comprises a magnetic probe array 1, a first coaxial line 2, a vacuum coaxial electrode (Feedthrough)3, a transmission line 4, a first-level local oscillator 5, a first eight-path power divider 6, a first frequency mixer 7, a second-level local oscillator 8, a second eight-path power divider 9, a second frequency mixer 10, a second coaxial line 11 and an acquisition module 12.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments, and all other embodiments obtained by a person skilled in the art based on the embodiments of the present invention belong to the protection scope of the present invention without creative efforts.

As shown in fig. 1, a system for measuring the wavenumber in the direction of the 4.6GHz lower clutter parallel magnetic field comprises two major parts, a vacuum side (tokamak vacuum chamber) and an atmospheric side. The vacuum side comprises a magnetic probe array 1 which is placed perpendicular to a background magnetic field and is fixed for a distance (d), a high-temperature-resistant phase-stable first coaxial line 2 and a vacuum coaxial electrode (Feedthrough)3, and the atmosphere side comprises a two-stage frequency reduction circuit and a high-speed data acquisition module 12. The outside of the magnetic probe coil in the magnetic probe array 1 is covered by a shielding barrel with a rectangular gap, and the coil is strictly vertical to the rectangular gap.

The 4.6GHz low noise wave is transmitted from the antenna and then propagates through the boundary plasma, the direction of the magnetic field of the boundary plasma is vertical to the background magnetic field, and then the boundary plasma is coupled by the magnetic probe array with a fixed distance. Because the bottom cover of the shielding barrel of the magnetic probe is provided with the rectangular gap, the probe is only sensitive to the magnetic disturbance in the direction vertical to the background magnetic field, and has good shielding effect on the microwave transmitted in other directions.

The low clutter coupled by the magnetic probe array is propagated by the high temperature resistant stable phase silicon dioxide coaxial line 2 in the tokamak vacuum chamber, and then is propagated out of the vacuum chamber through the vacuum coaxial electrode 3. After the signal is subjected to secondary frequency reduction at the atmosphere side, the signal is reduced to 20 MHz.

The secondary frequency reduction circuit comprises two local oscillators, a 4.9GHz first-stage local oscillator 5 and a 280MHz second-stage local oscillator 8. The signals from the two stages of local oscillators are divided into eight paths after passing through the first and second eight path power dividers 6 and 9, respectively. The 4.6GHz low noise wave coming out of the vacuum chamber is firstly mixed with a first-stage local oscillator 4.9GHz through a transmission line 4, is reduced to 300MHz after passing through a first frequency mixer 7, is then mixed with a second-stage local oscillator 280MHz, is reduced to 20MHz after passing through a second frequency mixer 10, and is finally accessed into an acquisition module 12 through a common second coaxial line 11. Since the 300MHz signal is connected to the band-pass filter with the bandwidth of 25MHz (as shown in FIG. 2), the final output signal of the down-conversion circuit is 20MHz + -12.5 MHz. In an actual plasma physical experiment, after 4.6GHz point-frequency low-noise waves emitted by an antenna interact with plasma, such as scattering, parametric decay and other processes, the frequency of the low-noise waves can be expanded to a certain extent. Therefore, based on the circuit structure, the phase of the pump wave (the pump wave is 4.6GHz spot frequency low clutter) at 4.6GHz can be obtained through FFT analysis, and the phase of 4.6GHz +/-12.5 MHz frequency space can also be obtained. The two-stage frequency reduction is adopted because the wavelet with the frequency of 4.6GHz +/-40 MHz can be generated after the interaction of the low noise wave and the plasma, and if the wavelet is directly mixed with the local oscillator with the frequency of 4.6GHz +/-20 MHz, the 20MHz microwave after the difference frequency has both the pump wave component and the low noise wave component, thereby not achieving the purpose of measuring the phase of the low noise wave.

As shown in fig. 3, the test results of this circuit show that the power and phase of the difference frequency circuit output is completely determined by the RF input signal, i.e., the 4.6GHz low noise wave. The down-converted signal accurately reflects the phase information and relative strength of the RF signal.

Fig. 4 and 5 show the test results of the system when the system is connected with the input of the 4.6GHz signal source. In FIG. 5, CH2-CH1 represent the phase difference between the 2 nd magnetic probe and the 1 st, CH3-CH2 represent the phase difference between the 3 rd magnetic probe and the 2 nd, and so on. It can be seen that the resulting spectrum after each FFT analysis is very peaked at 20MHz, with an amplitude 40db higher than the noise. Meanwhile, the phase difference between two adjacent channels obtained by FFT analysis

Is very stable. By

The parallel wave value can be obtained, thereby realizing the purpose of measuring the wave number in the direction of the low-clutter parallel magnetic field.

Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, but various changes may be apparent to those skilled in the art, and it is intended that all inventive concepts utilizing the inventive concepts set forth herein be protected without departing from the spirit and scope of the present invention as defined and limited by the appended claims.

Claims

1. The utility model provides a system for measure 4.6GHz low clutter parallel magnetic field direction wave number which characterized in that: the device comprises a magnetic probe array, a phase-stabilizing coaxial line, a vacuum coaxial electrode, a two-stage frequency reduction circuit and a high-speed data acquisition module;

low clutter signals in the plasma are coupled by a magnetic probe, transmitted to a vacuum flange by a high-temperature-resistant silicon dioxide stable phase coaxial line in a vacuum chamber, transmitted out of a Tokamak vacuum chamber by a vacuum coaxial electrode, transmitted to a difference frequency circuit by the coaxial line, subjected to difference frequency with two-stage local oscillation, and finally collected by a multi-channel high-speed collection module;

2. The system for measuring wavenumber in the direction of the parallel magnetic field of 4.6GHz low clutter according to claim 1, wherein:

the magnetic probe structure is only sensitive to magnetic disturbance parallel to the long edge of the gap, and has a shielding effect on wave magnetic fields in other directions.

3. The system for measuring wavenumber in the direction of the parallel magnetic field of 4.6GHz low clutter according to claim 1, wherein:

the two-stage difference frequency circuit comprises local oscillators of 4.9GHz and 280 MHz; the low clutter signal coupled out by the magnetic probe array firstly has a local oscillation difference frequency of 4.9GHz, then a band-pass filter with the central frequency of 300MHz and the bandwidth of 25MHz is accessed, and then the low clutter signal has a local oscillation difference frequency of 280MHz, and the original 4.6GHz radio frequency signal is subjected to frequency reduction to 20 MHz; the output signal strength of the frequency reducing circuit is determined by the 4.6GHz radio frequency signal, and the phase information of the frequency reducing circuit is not changed.

4. The system for measuring wavenumber in the direction of the parallel magnetic field of 4.6GHz low clutter according to claim 1, wherein:

the high-speed acquisition module is 8 channels and synchronously acquires the data with the sampling rate as high as 100 MS/s; thereby obtaining phase information thereof through FFT data processing.

5. The system according to claim 1, wherein the wave number of the 4.6GHz low-noise parallel magnetic field direction is measured by:

the low clutter coupled with the magnetic probe array is propagated by a stable phase coaxial line in the Tokamak vacuum chamber and then is propagated out of the vacuum chamber through a vacuum coaxial electrode, and the stable phase coaxial line is a high temperature resistant stable phase silicon dioxide coaxial line.

6. The system according to claim 1, wherein the wave number of the 4.6GHz low-noise parallel magnetic field direction is measured by:

the magnetic probe coil is formed by winding a silicon dioxide semi-rigid coaxial line inner conductor and is welded on an outer conductor, and the outside of the coil is covered by a stainless steel shielding barrel.