Method for identifying radial position and amplitude evolution of fishbone model based on fast frequency sweep microwave reflectometer

Abstract

The invention relates to a method for identifying the radial position and amplitude evolution of a fishbone model based on a fast frequency sweep microwave reflectometer, and belongs to the field of plasma diagnosis. The method is based on the physical principle that the fishbone model can cause the change of the electron density gradient at the position where the fishbone model is located, and the electron density gradient at the position where the fishbone model is located is the maximum. According to the method, the radial position of electron density distribution measured by a fast frequency sweep microwave reflectometer with high time and space resolution is derived, and the radial position and the amplitude evolution of the fishbone model are identified by extracting the radial position and the value of the maximum value of the electron density gradient of a plasma core area. Compared with the conventional method for identifying the position and amplitude of the fishbone model by using a line integral measurement result of soft X-ray diagnosis, the method has higher time and space resolution, can identify the radial position and amplitude evolution of the fishbone model more accurately, and is simple to operate, reliable and efficient.

Description

Technical Field

[0001] The invention belongs to the field of plasma diagnosis, and in particular relates to a method for identifying the radial position and amplitude evolution of a fishbone pattern based on a fast-sweep frequency microwave reflectometer. Background Art

[0002] The fast-sweep microwave reflectometer is an important diagnostic tool for measuring the radial distribution of electron density in magnetic confinement fusion plasma. Its basic principle is to emit detection microwaves of different frequencies to the plasma based on the radar principle, calculate the flight time required for reflection from the plasma cutoff layer to calculate the cutoff layer position corresponding to different frequencies, and then infer the plasma electron density distribution based on the dispersion relationship (see YM Wang et al. "Development of the W-banddensity profile and fluctuation reflectometer on EAST", Fusion Engineering and Design 88 (2013) 2950). With the continuous development of millimeter wave technology, the fast-sweep microwave reflectometer has become more and more mature and has been widely used in magnetic confinement fusion devices at home and abroad.

[0003] The fishbone mode is one of the important magnetohydrodynamic instabilities in the core region of the plasma of the tokamak device. Its existence has an important regulatory effect on the redistribution of fast particles and the broadening of the current distribution. Therefore, the accurate identification of the position and amplitude of the fishbone mode is of great significance. Usually, the fishbone mode can be identified from the soft X-ray diagnostic signal (see LQ Xu, et al Fishboneactivity in experimental advanced superconducting tokamak neutral beaminjection plasma", Phys. Plasmas (2015) 22, 122510), but the main disadvantages of this method are:

[0004] 1. Limited spatial resolution: Soft X-ray diagnosis is based on line integral measurement, which means it can only provide cumulative information along the line of sight, but cannot directly resolve fine structures within the field of view. This limits its application in scenarios requiring high spatial resolution.

[0005] 2. Greatly affected by the plasma state: The signal of soft X-ray diagnosis is closely related to the electron temperature and density of the plasma, impurity line radiation, etc. Therefore, its signal intensity will be affected by changes in the plasma state, affecting the accuracy of the diagnosis.

[0006] 3. High requirements for equipment and operation: Soft X-ray diagnostic equipment is usually complex and expensive, and also has high requirements for operation and maintenance. Summary of the invention

[0007] In order to solve the above problems existing in the measurement of fishbone model using soft X-rays, the present invention proposes a method for identifying the radial position and amplitude evolution of fishbone model based on fast-sweep microwave reflectometry. The core is that the fishbone model will modulate the electron density distribution at the position where the fishbone model is located, and the electron density gradient will change periodically, and the electron density gradient at the position where the fishbone model is located is the largest. Based on this phenomenon, the technical solution adopted by the present invention is as follows: the plasma electron density distribution in the plasma discharge is measured by fast-sweep microwave reflectometry, and then the position and value of the maximum density gradient in the plasma core area are extracted to identify the radial position and amplitude evolution of the fishbone model.

[0008] The specific technical solution of the present invention is: a method for identifying the radial position and amplitude of a fishbone pattern based on a fast-sweep microwave reflectometer, comprising the steps of:

[0009] Step 1: The magnetic confinement fusion device completes a discharge, and the fast-sweep microwave reflectometer works normally and collects signals;

[0010] Step 2: Invert the signal collected by the fast-sweep microwave reflectometer to obtain the radial distribution of the electron density;

[0011] Step 3, selecting the electron density distribution in the plasma core region;

[0012] Step 4, taking the derivative of the electron density distribution in the core region to obtain the radial position and value of the electron density gradient;

[0013] Step 5, extracting the radial position and value of the maximum density gradient;

[0014] Step 6: The radial position and value of the maximum density gradient are the radial position and amplitude of the fishbone model.

[0015] Compared with the fishbone model identification technology using soft X-ray diagnosis, the beneficial effects of the present invention are:

[0016] 1. The fast-sweep microwave reflectometer has high temporal and spatial resolution, and can measure an electron density distribution every 50 microseconds. In addition, the electron density distribution can almost cover the entire plasma region including the plasma core, and the radial interval between every two data points is about 1 cm, which makes it possible to study the fine structure of the fishbone model.

[0017] 2. Fast-sweep microwave reflectometer technology is mature, low-cost, and relatively simple to maintain. In addition, it has little interference with plasma.

[0018] 3. The processing method of the present invention is simple, easy for staff to understand, and has strong operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the workflow of the present invention;

[0020] Figure 2 This is an example of identifying the radial position and amplitude of a fishbone mold based on the method of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] like Figure 1 As shown, a schematic diagram of the workflow of a method for identifying the radial position and amplitude of a fishbone pattern based on a fast-sweep microwave reflectometer is provided, including the following method steps:

[0023] Step 1: The magnetic confinement fusion device completes a discharge, and the fast-sweep microwave reflectometer works normally and collects signals;

[0024] Including: Before the magnetic confinement fusion device starts discharging, the master control will give a trigger signal to the fast-sweep microwave reflectometer. When the discharge starts, the fast-sweep microwave reflectometer will emit detection microwaves into the plasma and collect and store the signals reflected back by the plasma.

[0025] Step 2: Invert the signal collected by the fast-sweep microwave reflectometer to obtain the radial distribution of the electron density;

[0026] Including: the collected signal is processed, inverted to obtain the radial distribution of plasma electron density and save it. At this time, the electron density distribution covers the plasma core, the base area and the SOL area, which is a complete electron density distribution. The specific processing method is: first, calculate the flight time required for the detection microwaves of different frequencies to be reflected from the plasma cutoff layer To calculate the corresponding cutoff layer position, and then infer the plasma electron density distribution based on the dispersion relation.

[0027] Step 3, selecting the electron density distribution in the plasma core region in step 2;

[0028] The method comprises: intercepting the complete electron density distribution obtained by inversion in step 2, and retaining only the electron density distribution in the core area of ​​the plasma.

[0029] Step 4, taking the derivative of the electron density distribution in the core region to obtain the radial position and value of the electron density gradient;

[0030] The method includes: taking the derivative of the electron density distribution in the core region obtained in step 3 with respect to the radial position, obtaining the radial position and value of the electron density gradient and saving them. The calculation formula is: , is the plasma electron density, R is the radial position of the plasma, is the electron density gradient.

[0031] Step 5, extracting the radial position and value of the maximum density gradient in step 4;

[0032] Including: From all the electron density gradients calculated in step 4, select the radial position and value of the maximum density gradient and save them.

[0033] The radial position and value of the maximum density gradient in step 6 and step 5 are the radial position and amplitude of the fishbone mold.

[0034] Including: the radial position and value of the maximum density gradient in step 5 can be used as the radial position and amplitude of the fishbone mold.

[0035] like Figure 2 As shown, Figure 2 The horizontal axis is time. Figure 2 (a) is the time evolution of the integral signal measured by soft X-ray diagnosis, and its periodic disturbances characterize the occurrence of fishbone model activity. The same parameter in the fusion device can be measured by different diagnostic systems based on different principles. Soft X-ray diagnosis is a conventional technology for measuring fishbone model activity, and its line integral signal can be used to identify the outbreak and signal intensity of fishbone model activity. The present invention is a new method for monitoring fishbone model activity, and the signal of soft X-ray diagnosis can be used as a reference. Figure 2 (b) is the contour map of the radial distribution of electron density measured by a fast-sweep microwave reflectometer, which evolves over time. The ordinate is the radial position R, and the color depth represents the value of the plasma electron density. The closer the color is to red, the greater the density value. Figure 2 (c) is to Figure 2 The radial distribution of electron density gradient obtained by differentiating the radial distribution of electron density with respect to the radial position in (b) evolves over time. The depth of color represents the value of the density gradient. The closer the color is to red, the larger the value of the density gradient. Figure 2 (d) is from Figure 2 (c) The radial position of the maximum density gradient extracted from the electron density gradient evolves over time. The radial position obtained here is the position of the fishbone mold. Figure 2 The (e) is from Figure 2(c) The maximum density gradient extracted from the electron density gradient evolves with time. The evolution of the value here with time can be used to characterize the change in the amplitude of the fishbone mode.

[0036] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for identifying the radial position and amplitude evolution of a fishbone pattern based on fast-sweep microwave reflectometry, characterized in that: Includes steps: Step 1: The magnetic confinement fusion device completes a discharge, and the fast-sweep microwave reflectometer works normally and collects signals; Step 2, obtaining the radial distribution of electron density based on the signal inversion collected by the fast-sweep microwave reflectometer; Step 3, selecting the electron density distribution in the plasma core region; Step 4, taking the derivative of the electron density distribution in the core region to obtain the radial position and value of the electron density gradient; Step 5, extracting the radial position and value of the maximum density gradient; Step 6: The radial position and value of the maximum density gradient are the radial position and amplitude of the fishbone model.

2. The method for identifying the radial position and amplitude evolution of a fishbone pattern based on fast-sweep microwave reflectometry according to claim 1, characterized in that: Step 1 specifically includes: before the magnetic confinement fusion device starts discharging, the master control will give a trigger signal to the fast-sweep microwave reflectometer. When the discharge starts, the fast-sweep microwave reflectometer emits detection microwaves into the plasma and collects and stores the signals reflected back by the plasma.

3. The method for identifying the radial position and amplitude evolution of a fishbone pattern based on fast-sweep microwave reflectometry according to claim 2, characterized in that: Step 2 specifically includes: processing the collected signal, inverting to obtain the radial distribution of plasma electron density and saving it. At this time, the electron density distribution covers the plasma core, the base area and the SOL area, which is a complete electron density distribution; the specific processing method is: first, by calculating the flight time required for the detection microwaves of different frequencies to be reflected from the plasma cutoff layer To calculate the corresponding cutoff layer position, and then infer the plasma electron density distribution based on the dispersion relation.

4. The method for identifying radial position and amplitude evolution of a fishbone pattern based on fast frequency sweep microwave reflectometry according to claim 3, characterized in that: Step 3 includes: intercepting the complete electron density distribution obtained by inverting step 2, and retaining the electron density distribution in the core area of ​​the plasma.

5. The method for identifying radial position and amplitude evolution of a fishbone pattern based on fast frequency sweep microwave reflectometry according to claim 4, characterized in that: Step 4 comprises: taking the derivative of the electron density distribution in the core region obtained in step 3 with respect to the radial position, obtaining the radial position and value of the electron density gradient and saving them; the calculation formula is: , is the plasma electron density, R is the radial position of the plasma, is the electron density gradient.

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