A method for identifying radial position and amplitude evolution of fishbone mode based on fast-sweep microwave reflectometry

Abstract

The present invention relates to a method for identifying the radial position and amplitude evolution of a fishbone pattern based on a fast-sweep microwave reflectometer, and belongs to the field of plasma diagnosis. The physical principle underlying the method is that a fishbone pattern causes a change in the electron density gradient at its location, and that the electron density gradient is greatest at the location of the fishbone pattern. The present invention radially differentiates the electron density distribution obtained by a fast-sweep microwave reflectometer with high temporal and spatial resolution, and extracts the radial position and value of the maximum electron density gradient in the plasma core region to identify the radial position and amplitude evolution of the fishbone pattern. Compared to conventional methods of identifying the position and amplitude of a fishbone pattern using line integral measurement results from soft X-ray diagnosis, the present invention has higher temporal and spatial resolution, can more accurately identify the radial position and amplitude evolution of a fishbone pattern, is simple to operate, and is 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 microwave reflectometer. Background Art

[0002] Fast-sweep microwave reflectometry is an important diagnostic tool for measuring the radial distribution of electron density in magnetic confinement fusion plasmas. Its basic principle is to transmit probe microwaves of different frequencies into the plasma based on the radar principle. The position of the cutoff layer corresponding to different frequencies is calculated by calculating the flight time required for the microwaves to be reflected from the plasma cutoff layer. The plasma electron density distribution is then inferred based on the dispersion relation (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, fast-sweep microwave reflectometry has become increasingly mature and is widely used in magnetic confinement fusion devices both domestically and internationally.

[0003] Fishbone mode is one of the most important magnetohydrodynamic instabilities in the plasma core of a tokamak device. Its existence plays a significant role in regulating the redistribution of fast particles and the broadening of the current distribution. Therefore, accurate identification of the position and amplitude of fishbone mode is of great significance. Fishbone mode can usually be identified from soft X-ray diagnostic signals (see LQ Xu, et al. Fishbone activity in experimental advanced superconducting tokamak neutral beam injection plasma", Phys. Plasmas (2015) 22, 122510). However, the main disadvantages of this method are:

[0004] 1. Limited spatial resolution: Soft X-ray diagnosis is based on line integral measurements, which means it can only provide cumulative information along the line of sight and 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 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 diagnosis.

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

[0007] To address the aforementioned issues with measuring fishbone patterns using soft X-rays, the present invention proposes a method for identifying the radial position and amplitude evolution of fishbone patterns using fast-sweep microwave reflectometry. The core principle is that the fishbone pattern modulates the electron density distribution at its location, causing the electron density gradient to change periodically, with the electron density gradient being maximum at the location of the fishbone pattern. Based on this phenomenon, the present invention employs the following technical solution: Fast-sweep microwave reflectometry is used to measure the plasma electron density distribution during a plasma discharge. The location and value of the maximum density gradient in the plasma core region are then extracted to identify the radial position and amplitude evolution of the fishbone pattern.

[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 operates normally and collects signals;

[0010] Step 2: Obtain the radial distribution of electron density based on the signal inversion collected by the fast-sweep microwave reflectometer;

[0011] Step 3: Select the electron density distribution in the plasma core area;

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

[0013] Step 5: extract 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 mold 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, capable of measuring an electron density distribution every 50 microseconds. Furthermore, the electron density distribution covers almost the entire plasma region, including the plasma core, with radial data points spaced approximately 1 cm apart, making it possible to study the fine structure of the fishbone model.

[0017] 2. Fast-sweep microwave reflectometry technology is mature, low-cost, and relatively simple to maintain. Furthermore, it causes minimal disruption to the plasma.

[0018] 3. The treatment method of the present invention is simple, easy for staff to understand, and highly operable. 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 pattern based on the method of the present invention. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate 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 may be combined with each other as long as they do not conflict with each other.

[0022] like Figure 1 As shown in FIG, 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, which includes the following steps:

[0023] Step 1: The magnetic confinement fusion device completes a discharge, and the fast-sweep microwave reflectometer operates 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: Obtain the radial distribution of electron density based on the signal inversion collected by the fast-sweep microwave reflectometer;

[0026] The process includes: processing the collected signals, inverting and saving the radial distribution of plasma electron density. The electron density distribution now 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 includes: intercepting the complete electron density distribution obtained by inversion in step 2, and retaining only the electron density distribution in the plasma core region.

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

[0030] The process includes: taking the derivative of the electron density distribution of 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 plasma radial position, 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 model.

[0035] like Figure 2 As shown, Figure 2 The horizontal axis is time. Figure 2 (a) shows the time evolution of the integrated signal measured by soft X-ray diagnostics. Its periodic perturbations indicate the presence of fishbone mode activity. The same parameter in a fusion device can be measured by different diagnostic systems based on different principles. Soft X-ray diagnostics is a common technique for measuring fishbone mode activity, and its line integral signal can be used to identify bursts and signal strength. This presents a new method for monitoring fishbone mode activity, and the soft X-ray diagnostic signal can be used as a reference. Figure 2 (b) is the contour map of the radial distribution of electron density obtained by fast-sweep microwave reflectometry, which evolves over time. The vertical axis 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 radial position in (b) evolves over time. The depth of color represents the size of the density gradient value. The closer the color is to red, the larger the density gradient value. 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 location of the fishbone model. Figure 2 The (e) is from Figure 2(c) The maximum density gradient extracted from the electron density gradient evolves over time. The temporal evolution of this value 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 are only specific embodiments of the present invention and are 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: Including steps: Step 1: The magnetic confinement fusion device completes a discharge, and the fast-sweep microwave reflectometer operates normally and collects signals; Step 2: Obtain the radial distribution of electron density based on the signal inversion collected by the fast-sweep microwave reflectometer; Step 3: Select the electron density distribution in the plasma core area; Step 4: Derivative the electron density distribution in the core area to obtain the radial position and value of the electron density gradient; the calculation formula is: , is the plasma electron density, R is the plasma radial position, is the electron density gradient; Step 5: extract 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 mold; 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.

2. The method for identifying 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 send 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.

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 3 includes: intercepting the complete electron density distribution obtained by inversion in step 2, and retaining the electron density distribution in the plasma core area.

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