A microwave reflectometer system capable of realizing self-calibration

Abstract

The present invention discloses a microwave reflectometer system capable of realizing self-calibration. The system fixes a copper wire passing through the center of the waveguide cross section at the end of the corrugated waveguide of the existing microwave reflectometer, so that while the detection microwave can be normally emitted into the plasma, a part of the microwave will be reflected by the copper wire and returned to the optical path. In this way, the intermediate frequency signal obtained after mixing by the high-frequency mixer of the microwave reflectometer contains both the plasma density distribution information and the fixed copper wire position information. Two acquisition circuits are arranged after the IF end of the high-frequency mixer. Based on the measurement path signal and the calibration path signal collected by the acquisition system, dynamic real-time calibration of the plasma density distribution information is realized. The system realizes self-calibration by adjusting the optical path and the electronic part of the microwave reflectometer system, and eliminates the influence of vibration generated during the operation of the fusion experimental device on the density distribution measurement in real time.

Description

Technical Field

[0001] The invention relates to the technical field of microwave reflectometers, and in particular to a microwave reflectometer system capable of realizing self-calibration. Background Art

[0002] The calibration method of the existing plasma density distribution measurement system on the advanced fusion experimental device, the Eastern Super Torus (EAST), is to use a copper cover to cover the end of the microwave transmission optical path before the discharge begins, and adjust the electronic part of the reflectometer system to the "calibration mode". Through multiple iterations, the waveform of the tuning voltage applied to the continuous wave generator (voltage controlled oscillator - VCO) is fine-tuned to make the flight time of microwaves of each frequency to the copper cover position the same, that is, the dispersion effect on the long-distance microwave transmission path is eliminated, and the flight time of this part is deducted during data processing. After the calibration is completed, the copper cover needs to be manually removed to ensure that the optical path is unobstructed, and the electronic part is adjusted to the "measurement mode". The calibration process usually takes about 1 hour and requires human operation near the device. It is impossible to achieve discharge gap calibration or real-time self-calibration, so the impact of vibration generated during the operation of the device on the optical path cannot be eliminated in real time. At the same time, the effective duration of a calibration is not enough to cover the long experimental cycle of the fusion experimental device, that is, after a period of time, the dispersion effect of the frequency continuous wave in the optical path will reappear, affecting the measurement accuracy.

[0003] It can be seen that the existing calibration method of microwave reflectometers requires major adjustments to the electronics and complete blocking of the optical path. The operation is complicated and time-consuming, and it is even impossible to calibrate during the discharge interval, let alone real-time calibration. Summary of the invention

[0004] The purpose of the present invention is to provide a microwave reflectometer system capable of self-calibration. The system realizes self-calibration by adjusting the optical path and electronic parts of the microwave reflectometer system, and eliminates the influence of vibration generated during the operation of a fusion experimental device on density distribution measurement in real time.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A microwave reflectometer system capable of realizing self-calibration, wherein a copper wire passing through the center of the waveguide cross section is fixed at the end of a corrugated waveguide of an existing microwave reflectometer, so that while detection microwaves can be normally emitted into a plasma, a portion of the microwaves will be reflected back to the optical path by the copper wire, so that the intermediate frequency signal obtained after mixing by a high-frequency mixer of the microwave reflectometer contains both plasma density distribution information and the position information of the fixed copper wire;

[0007] Two acquisition circuits are arranged after the IF end of the high-frequency mixer. The intermediate frequency signal drawn from the IF end of the high-frequency mixer is divided into two paths by a power divider: one path passes through a 124-176MHz bandpass filter and becomes a measurement path signal containing only plasma density distribution information. The measurement path signal is amplified and mixed twice before being acquired by the acquisition system;

[0008] The other path passes through a 90-110MHz bandpass filter and becomes a calibration path signal containing only the copper wire position information. After being amplified by an amplifier, the calibration path signal is mixed with a fixed frequency signal generated by a 120MHz crystal oscillator through a low-frequency mixer and then collected by the acquisition system.

[0009] Based on the measurement path signals and calibration path signals collected by the acquisition system, dynamic real-time calibration of the plasma density distribution information is achieved.

[0010] It can be seen from the technical solution provided by the present invention that the system can achieve self-calibration by adjusting the optical path and electronic parts of the microwave reflectometer system, and can eliminate the influence of vibrations generated during the operation of the fusion experimental device on the density distribution measurement in real time, thereby accurately measuring the density distribution of plasma and providing a reference solution for the future ITER plan and other fusion devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0012] Figure 1 A schematic diagram of the structure of a microwave reflectometer system capable of realizing self-calibration provided by an embodiment of the present invention;

[0013] Figure 2 It is a schematic diagram of the dynamic real-time calibration of plasma density distribution information according to an embodiment of the present invention. DETAILED DESCRIPTION

[0014] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, which does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] like Figure 1FIG. 1 is a schematic diagram of the structure of a microwave reflectometer system capable of realizing self-calibration provided by an embodiment of the present invention. Figure 1The invention comprises: 1 is an arbitrary waveform generator AWG (Arbitrary Waveform Generator), which is used to generate a preset tuning voltage so that the microwave source can output microwaves with continuously changing frequencies; 2 is a voltage controlled oscillator VCO (Voltage Controlled Oscillator), which is used to receive the scanning voltage waveform sent by 1 and output a frequency modulated continuous wave, and the frequency variation range is 8 to 12.5GHz; 3 is a power divider PD (Power Divider), which is used to divide the wave output by the VCO into two paths, which are used as reference path signals and measurement path signals respectively; 4 and 5 are frequency multipliers for the measurement path and reference path respectively, which are used to multiply the frequency of the wave output by the VCO to a suitable frequency range. For the electronic system of the Q band (33-50GHz), a 4-frequency multiplier is required, and for the electronic system of the V band (50-75GHz), a 6-frequency multiplier is required; 6 and 7 are isolators (Isolators) for the measurement path and reference path respectively, which are used to filter out the echoes reflected multiple times in the electronic device to enhance the signal-to-noise ratio; 8 is a directional coupler DC (Directional Coupler), which can transmit the detection signal backward while receiving the measurement signal carrying the density distribution information returned from the plasma, and lead the measurement signal from another path; 9 is an orthogonal mode converter OT (Ortho-Mode Transducer), which can realize the separation and synthesis of orthogonal polarization signals. Due to the necessity of measuring the zero point of plasma density and the demand to widen the measurement range of density distribution as much as possible, the microwave reflectometer in the Q band needs to contain detection waves of two polarization modes: ordinary wave (O mode) and extraordinary wave (X mode). The orthogonal mode converter OT can help realize duplex transmission, which greatly reduces the redundancy of the electronic system; 10 is the antenna; 11 is the coupling lens, which measures the parameters of the two. Through proper optical path alignment, the power of the detection microwave can be utilized to the maximum extent and the signal-to-noise ratio can be improved; 12 is the corrugated waveguide, which is used to transmit microwave signals over long distances; 13 is a high-frequency bandpass filter, which mainly filters out the interference of multiple reflections of the signal between devices. Secondly, it can also filter out the broadband and high-energy waves generated by high-energy electrons bombarding the device wall when the discharge breaks, and to a certain extent protect the mixer and other devices after the optical path. For the electronic system in the Q band, Use a 33-50GHz bandpass filter. For the V-band system, use a 50-75GHz bandpass filter. 14 is a high-frequency mixer, which generally has three ports: LO, RF, and IF. 15 is a 124-176MHz bandpass filter. After calculation and experimental verification, the intermediate frequency corresponding to the phase delay caused by the plasma to the signal falls within the passband range of the bandpass filter. Therefore, 15 can be used to filter out clutter and enhance the signal-to-noise ratio. 16 is an amplifier, which is used to amplify the signal amplitude, enhance the signal-to-noise ratio, and facilitate data processing. 17 is a 150MHz crystal oscillator, which is used to generate a fixed-frequency signal to perform secondary mixing with the intermediate frequency signal after the primary mixing. 18 is a low-frequency mixer, whose LO terminal is connected to the 150MHz fixed-frequency signal generated by 17, the RF terminal is connected to the primary mixing signal amplified by 16, and the IF terminal is led to the acquisition card. 19 is an acquisition system, which can meet the data acquisition of high throughput during long pulse discharge. .

[0016] The system of the embodiment of the present invention fixes a copper wire 27 passing through the center of the waveguide cross section at the end of the corrugated waveguide 12 of the existing microwave reflectometer, such as Figure 1 As shown in the cross-sectional view on the upper left, instead of using the copper cover to completely block the optical path as in the prior art calibration mode, a portion of the microwaves can be reflected back to the optical path by the copper wire while the detection microwaves can be normally emitted into the plasma, so that the intermediate frequency signal obtained after mixing by the high-frequency mixer 14 of the microwave reflectometer contains both the plasma density distribution information and the position information of the fixed copper wire 27;

[0017] In the existing scheme, the intermediate frequency of the copper cover shielded part is a straight line, which is deducted as a constant during data processing. However, in fact, as the device runs, the dispersion effect will gradually appear, that is, there is a certain error in the method of deducting the constant. The system described in the embodiment of the present invention takes this part of the error into consideration. While measuring the plasma density distribution, it also measures the position of the fixed copper wire 27 in real time. Even if the dispersion effect is not completely eliminated, the intermediate frequency change of the copper wire 27 can be deducted through post-data processing instead of deducting a constant, thereby minimizing the error to the greatest extent and realizing real-time self-calibration of the system.

[0018] Based on this idea, in the embodiment of the present invention, two acquisition circuits are arranged after the IF end of the high-frequency mixer 14. The intermediate frequency signal drawn from the IF end of the high-frequency mixer 14 is divided into two paths by the power divider 21: one path passes through a 124-176MHz bandpass filter to become a measurement path signal containing only plasma density distribution information, and the measurement path signal is amplified and mixed twice before being acquired by the acquisition system 19;

[0019] The other path passes through a 90-110MHz bandpass filter 22 to become a calibration path signal containing only the position information of the copper wire 27. The calibration path signal is amplified by an amplifier 23, mixed with a fixed frequency signal generated by a 120MHz crystal oscillator 25 through a low-frequency mixer 24, and then collected by the collection system 19.

[0020] Based on the measurement path signals and calibration path signals collected by the acquisition system 19, dynamic real-time calibration of the plasma density distribution information is achieved.

[0021] In the specific implementation, after the measurement path signal is processed, what is obtained is the intermediate frequency change caused by the cutoff reflection of microwaves of various frequencies reaching the plasma;

[0022] After the calibration path signal is processed, the intermediate frequency signal obtained is the microwave of each frequency reaching the copper wire 27 and being reflected;

[0023] The intermediate frequency signal of the calibration path is deducted from the measurement path to eliminate the dispersion effect during the discharge and realize dynamic real-time calibration of the plasma density distribution information.

[0024] like Figure 2 FIG. 1 is a schematic diagram of a dynamic real-time calibration of plasma density distribution information according to an embodiment of the present invention. Figure 2 Figures (a) and (b) are respectively the signal of the plasma measured by the self-calibration microwave reflectometer and the signal of the copper wire used for calibration. The horizontal axis is time, which corresponds to the emission frequency one by one, and the vertical axis is the intermediate frequency, which is proportional to the flight time of the microwave. It can be seen that the time for waves of each frequency to reach the copper wire is slightly different. This is the additional dispersion generated during the operation of the device, which is difficult to completely eliminate through calibration before the experiment. The present invention can measure the plasma and the copper wire at the same time, and calibrate and eliminate the error caused by the dispersion in real time. The specific method is to extract a main peak of the intermediate frequency of the plasma signal and the intermediate frequency of the copper wire signal according to the intensity (that is, the curve of the evolution of the intermediate frequency with time in Figures (a) and (b)), and subtract the two main peaks to obtain the calibrated intermediate frequency signal. Based on the calibrated intermediate frequency signal, the phase delay caused by the plasma to the detection microwaves of each frequency is calculated, thereby calibrating and eliminating the error caused by the dispersion in real time; as shown in FIG. Figure 2 As shown in (c), the phase curve after calibration is slightly lower than that before calibration. Figure 2 (d) is the final calculated density distribution result. It can be seen intuitively that the calibrated density distribution as a whole has moved two to three centimeters outward and is consistent with the measurement result of another density diagnostic system, indicating that the present invention is of great significance for accurately measuring plasma density distribution.

[0025] In addition, based on the structure of the system, the spectrum of the position of the copper wire 27 is measured, and the least square method is used for multiple iterations to fine-tune the scanning voltage waveform so that the flight time of waves of each frequency to reach the copper wire 27 is the same, eliminating the dispersion effect caused by the waveguide.

[0026] In the specific implementation, since the frequency of the collected signal is proportional to the flight time, that is, proportional to the optical path length, and the position of the copper wire 27 is far away from the plasma position, the intermediate frequency difference is about 30-40MHz. If you want to observe the two signals at the same time, the sampling rate must be no less than 80MHz. The current acquisition system NIPXIe-5105 has a maximum sampling rate of 60MHz, which does not meet the requirements. In addition, the amount of data at a high sampling rate brings a greater burden on later data storage and backup. Therefore, it is necessary to down-sample the signal before collecting it. Since the frequency variation range of the signal is not large, it can be mixed with a fixed frequency source to reduce the frequency. In this way, the frequency variation range of the two signals is no more than 30MHz. At this time, using PXIe-5105 to set the sampling rate to 60MHz can meet the acquisition requirements.

[0027] In addition, during the platform testing phase, it is necessary to apply a scanning voltage of 0.45V and 5V at the high and low levels to the voltage-controlled oscillator VCO, measure it with a step size of 2mV, take the inverse function of the obtained frequency-voltage curve, and import it into the arbitrary waveform generator AWG with a scanning period of 16 microseconds to complete the linearization of the microwave source output.

[0028] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to professional and technical personnel in the field.

[0029] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A microwave reflectometer system capable of self-calibration, characterized in that: The system fixes a copper wire passing through the center of the waveguide cross section at the end of the corrugated waveguide of the existing microwave reflectometer, so that while the detection microwave energy can be normally emitted into the plasma, a part of the microwave will be reflected back to the optical path by the copper wire, so that the intermediate frequency signal obtained after mixing by the high-frequency mixer of the microwave reflectometer contains both the plasma density distribution information and the fixed copper wire position information; Two acquisition circuits are arranged after the IF end of the high-frequency mixer. The intermediate frequency signal drawn from the IF end of the high-frequency mixer is divided into two paths by a power divider: one path passes through a 124-176MHz bandpass filter and becomes a measurement path signal containing only plasma density distribution information. The measurement path signal is amplified and mixed twice before being acquired by the acquisition system; The other path passes through a 90-110MHz bandpass filter and becomes a calibration path signal containing only the copper wire position information. After being amplified by an amplifier, the calibration path signal is mixed with a fixed frequency signal generated by a 120MHz crystal oscillator through a low-frequency mixer and then collected by the acquisition system. Based on the measurement path signal and calibration path signal collected by the acquisition system, dynamic real-time calibration of plasma density distribution information is realized. The specific process is as follows: After the measurement path signal is processed, what is obtained is the change in the intermediate frequency caused by the cutoff reflection of microwaves of various frequencies reaching the plasma; After the calibration path signal is processed, the intermediate frequency signal is obtained after the microwaves of each frequency reach the copper wire and are reflected; The intermediate frequency signal of the calibration path is deducted from the measurement path to eliminate the dispersion effect during the discharge and realize dynamic real-time calibration of the plasma density distribution information.

2. The microwave reflectometer system capable of self-calibration according to claim 1, characterized in that: Based on the structure of the system, the spectrum of the copper wire position is measured, and the least square method is used for multiple iterations to fine-tune the scanning voltage waveform so that the flight time of waves of each frequency to reach the copper wire is the same, eliminating the dispersion effect caused by the waveguide.

3. The microwave reflectometer system capable of self-calibration according to claim 1, characterized in that: The intermediate frequency signal of the calibration path is deducted from the measurement path to eliminate the dispersion effect during the discharge. The specific process is as follows: Extract a main peak from the intermediate frequency of the plasma signal and the intermediate frequency of the copper wire signal respectively according to their intensity, subtract the two main peaks to obtain a calibrated intermediate frequency signal; The phase delay caused by the plasma to the detection microwaves of each frequency is calculated based on the calibrated intermediate frequency signal, so that the error caused by dispersion can be calibrated and eliminated in real time.

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