Compact ring plasma velocity calculation method and measurement system

Abstract

The invention discloses a compact ring plasma velocity calculation method and a measurement system, and relates to the technical field of plasma diagnosis, and the method comprises the following steps: measuring the density signal data of a to-be-measured compact ring plasma based on two optical fiber interferometers, and measuring the density signal data of a reference source; carrying out peak value searching on the to-be-measured compact ring plasma density through an algorithm, and selecting the time at the density peak value as a speed starting point of the to-be-measured compact ring plasma; respectively obtaining a time difference array of the compact ring plasma to be measured flying over the two optical fiber interferometers through the intervals corresponding to the two points; the average speed of the compact ring plasma to be measured is obtained by using the distance between the time difference array and the two optical fiber interferometers; the plasma velocity is measured based on the density signals of the optical fiber interferometers, the plasma motion velocity is measured through the time difference of the to-be-measured plasma flying over the two optical fiber interferometers, and a more accurate density starting point interval is obtained through an algorithm.

Description

Technical Field

[0001] The invention relates to the technical field of plasma diagnosis, and in particular to a compact ring plasma velocity calculation method and a measurement system. Background Art

[0002] The compact ring injection system is a technology for core charging of fusion devices. Its characteristic is that it can produce high-speed, high-density self-organized plasma clusters. In magnetic confinement fusion experimental devices, the compact ring injection system is currently the most promising solution for realizing core charging on large tokamaks. Using a compact ring to inject plasma into a tokamak requires the compact ring plasma to pass through an external strong magnetic field into the core of the fusion reactor. When the compact ring plasma passes through the gradient magnetic field, a very high speed is required to achieve the conditions for core charging. Therefore, it is particularly important to study whether the speed of the compact ring plasma can meet the conditions for passing through the gradient magnetic field.

[0003] The calculation method of macroscopic velocity of high temperature plasma is still a technology that needs to be further improved. The existing methods such as magnetic probe measurement have large errors in the measurement results under strong magnetic fields because the measurement accuracy of magnetic probe is affected by the magnetic field. In the compact ring injection system, the influence of magnetic field is often not negligible. Therefore, a new method for calculating the velocity of compact ring plasma is developed. Summary of the invention

[0004] The purpose of the present invention is to provide a compact ring plasma velocity calculation method and measurement system to solve the technical problems that the existing contact measurement of magnetic probes causes flow field disturbances and the measurement accuracy is limited by the magnetic field and cannot be directly applied to the compact ring plasma velocity measurement.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for calculating the velocity of a compact ring plasma comprises the following steps:

[0007] Based on two fiber optic interferometers, density signal data of the compact ring plasma to be measured is measured, a plasma source of the same gas is used as a reference source, and the density signal data of the reference source is measured to obtain a curve of the change of the two plasma density signal data over time;

[0008] Data preprocessing is performed on the obtained two plasma density signal data, and a peak search is performed on the density of the compact ring plasma to be measured through an algorithm, and the time at the density peak is selected as the starting point for calculating the velocity of the compact ring plasma to be measured;

[0009] The density peak point is used as a reference for substitution, and the 1 / e point corresponding to the peak point is calculated through the corresponding peak point. The time difference array of the compact ring plasma to be measured flying through the two fiber interferometers is obtained through the intervals corresponding to the two points.

[0010] The average speed of the compact ring plasma flying across the two fiber interferometers is obtained by using the time difference value and the distance between the two fiber interferometers according to the speed formula.

[0011] As a further solution of the present invention: the specific method for measuring the plasma density to be measured is: using a laser as an excitation light source, and using a 1×2 beam splitter to divide the light source into two beams; one beam is used as a reference beam, and the other beam is used as a detection beam, and two fiber optic collimators are used as transmitters and receivers to measure the change in the optical path of the electromagnetic wave passing through the plasma, thereby calculating the plasma density.

[0012] As a further solution of the present invention: performing data preprocessing on the obtained two plasma density signal data into standardization and normalization data preprocessing;

[0013] The peak search algorithm for the density of the compact ring plasma to be measured is to use a sliding window peak monitoring algorithm to obtain the peak value of the density signal;

[0014] The time when the first complete density peak appears is taken as the starting point of the compact ring plasma velocity.

[0015] As a further solution of the present invention: standardizing and normalizing the two density signal data, the mathematical formula of the algorithm used in this process is:

[0016]

[0017] Among them, x is the data after standardized calculation, x i is the original density signal collected by the fiber interferometer, μ is the original data mean, σ is the original data standard deviation, x′ is the normalized data, and x min is the minimum value of the data after normalization calculation, x max The maximum value of the data after normalization.

[0018] As a further solution of the present invention: the density peak point is used as a reference for substitution. The specific method is: the peak point is replaced by the horizontal coordinate time t and the vertical coordinate density n e , calculate the vertical coordinate n after substitution e / e, and substituted it onto the density curve by the interpolation method to obtain the 1 / e point position corresponding to the density peak point, and the time difference array of the compact ring plasma flying over the two fiber interferometers is obtained through the intervals corresponding to the two points.

[0019] As a further solution of the present invention: the interpolation method is specifically: constructing a polynomial function P(x) through existing data, and substituting the known y into it to obtain the interpolated x. The mathematical formula used in this process is:

[0020]

[0021] As a further solution of the present invention: the specific method for calculating the average speed of the compact ring plasma to be measured flying over the two fiber interferometers is: using the time difference array and the position distance of the two fiber interferometers, the average speed of the compact ring plasma to be measured is calculated according to the speed formula, and the speed formula is:

[0022]

[0023] Where s is the position distance between the two fiber interferometers, and Δt is the calculated time difference array.

[0024] As a further solution of the present invention: a compact ring plasma velocity measurement system, comprising:

[0025] A measuring device, which is used to measure the compact ring plasma to be measured based on a fiber interferometer, and obtain a curve of density signal data changing with laser frequency;

[0026] A processing device is used to calibrate the time starting point of the macroscopic velocity of a compact ring plasma. A gas plasma source of the same type is used as a reference source to measure the density signal of the compact ring plasma, and the time when the first complete peak appears is selected as the time starting point. The actual velocity distribution of the compact ring plasma to be measured is obtained by substitution based on the time starting point.

[0027] As a further solution of the present invention: the measuring device includes: a fiber laser as an excitation light source, the output end of the laser is connected to the optical path system, and the excitation light enters the compact ring host through the optical path system to interact with the particles; the measuring device also includes: a fiber coupler for splitting and combining optical signals, the fiber coupler splits the laser into two beams of laser light with the same phase and amplitude; a fiber attenuator for attenuating the optical power transmitted by the optical fiber to a certain extent, as well as a photodetector for converting signals and a fiber collimator for coupling the laser into a fiber; a processor for data acquisition, the processor scans the laser frequency and records the density signal data detected by the photodetector to obtain a curve of the density signal data changing with the laser frequency.

[0028] As a further solution of the present invention: the processing device comprises:

[0029] A first processing module is used to perform data preprocessing on the two density signal data of the compact ring plasma by standardization and normalization;

[0030] A second processing module is used to perform a peak search on the density of the compact ring plasma using a sliding window peak monitoring algorithm on the pre-processed data to obtain a peak value of the density signal;

[0031] The third processing module is used to replace the time when the first complete density peak appears as a reference, and obtain the / e point corresponding to the peak point through the corresponding peak point, and calculate the macroscopic speed by obtaining the time difference between the compact ring plasma to be tested flying through the two fiber optic interferometers through the intervals corresponding to the two points.

[0032] Beneficial effects of the present invention: The present invention measures plasma velocity based on the density signal of the fiber optic interferometer, measures the plasma movement velocity by the time difference when the measured plasma flies through two fiber optic interferometers, and obtains a more accurate density starting point interval through an algorithm. It is a new measurement technology that will not be affected by electrical and magnetic interference, has the advantages of high precision, strong anti-interference and wide applicability, and can be widely promoted and applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described below in conjunction with the accompanying drawings.

[0034] Figure 1 A schematic diagram of the implementation process of a plasma velocity calculation method is provided for an embodiment of the present invention;

[0035] Figure 2 A schematic diagram of the position of using a fiber interferometer to collect density on a compact ring injection device mentioned in an embodiment of the present invention;

[0036] In the figure: 1. Window No. 1 of the fiber optic interferometer, 2. Window No. 2 of the fiber optic interferometer, 3. Window No. 3 of the fiber optic interferometer.

[0037] Figure 3 Provides a flow chart for implementing a plasma velocity calculation method according to an embodiment of the present invention;

[0038] Figure 4 A schematic diagram of the structure of a plasma velocity measurement system provided by an embodiment of the present invention;

[0039] Figure 5 A schematic diagram of the structure of a measuring device in a plasma velocity measurement system provided in an embodiment of the present invention;

[0040] Figure 6 A schematic diagram of a speed calculation interval selected on a density signal provided in an embodiment of the present invention.

[0041] In the figure: 100, measuring device; 101, fiber laser; 102, fiber coupler; 103, fiber attenuator; 104, photodetector; 105, fiber collimator; 106, processor; 200, processing device; 210, first processing module; 220, second processing module; 230, third processing module. DETAILED DESCRIPTION

[0042] The compact ring plasma velocity calculation method provided by the present invention is described in detail below. 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. If no specific conditions are specified in the embodiments of the present invention, the conventional conditions in the field or the conditions recommended by the manufacturer are followed. The reagents or instruments used in the embodiments of the present invention, which do not indicate the manufacturer, are all conventional products that can be purchased commercially. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work belong to the scope of protection of the present invention.

[0043] Specifically, see Figure 1-Figure 6 As shown, the present invention proposes a method for calculating the velocity of compact ring plasma based on a sliding window and simulated annealing algorithm. The method can be used to intercept the density interval of compact ring plasma to calculate the time of flying over two fiber interferometer windows, so as to infer the velocity of compact ring plasma.

[0044] The basic processing flow involved in the compact ring plasma velocity calculation method provided by the embodiment of the present invention is as follows: Figure 1 As shown, the specific steps include:

[0045] Step S1: Collect density signals of compact ring plasma, where the density signals include Figure 2 The density signals collected by the fiber optic interferometer window No. 1 and the fiber optic interferometer window No. 3, wherein the three groups of windows of the fiber optic interferometer are used to verify the collected signal data, and the two fiber optic interferometers are distributed in different windows to realize calculations with different spacings.

[0046] Specifically, the compact ring plasma density is collected using a homodyne Mach-Jeanne laser interferometer, and the device is mainly composed of a fiber laser, a fiber coupler, a fiber attenuator, a wavelength division multiplexer, a collimator and a photodetector.

[0047] An ultra-narrow linewidth laser of 1 kHz and 1550 nm is used as the excitation light source, and a 1×2 beam splitter is used to split the light source into two beams: one as a reference beam and the other as a detection beam, which are located on both sides of the plasma 1 through two fiber collimators as a transmitter and a receiver.

[0048] The reference beam and the detection beam are sent to the two input ports of the 3×3 coupler, leaving one input port empty. In order to avoid the echo of the laser, the empty input port is covered with a light shielding cap, and the three outputs are connected to the photodetector.

[0049] During the discharge of the compact ring injection system, the same inert gas is used as a reference source, and the fiber interferometer accurately measures the time evolution of the plasma electron density.

[0050] Step S2: processing the density signal data is to perform data preprocessing on the obtained two density signal data, including data standardization and normalization;

[0051] The mathematical formula of the algorithm used in this process is:

[0052]

[0053] Among them, is the original density signal collected by the fiber interferometer, μ is the mean of the original data, and σ is the standard deviation of the original data.

[0054] The peak search algorithm for the density of the compact ring plasma to be measured is to use a sliding window peak monitoring algorithm to obtain the peak value of the density signal;

[0055] The time when the first complete density peak appears is taken as the starting point of the compact ring plasma velocity.

[0056] Use the sliding window algorithm to search for the peak value of the compact ring plasma density. Define a window size and search for the peak value in each window. The specific steps are as follows:

[0057] Step 1: Define a window size, which represents the range of peaks to be detected in the time series.

[0058] Step 2: Starting from the beginning of the sequence, slide the window to the end of the sequence.

[0059] Step 3: Calculate the peak value in each window according to the simulated annealing algorithm.

[0060] Step 4: Move the window one position to the right according to the time sequence.

[0061] Step 5: Adaptively adjust the window size. If the peak amplitude in the current window is less than or equal to 80% of the maximum value of the entire data set, reduce the window size to better adapt to the peak with a smaller amplitude.

[0062] Step 31: Use a simulated annealing algorithm to perform a peak search on the density of the compact ring plasma. The process may specifically include the following steps:

[0063] Step 32: Randomly find a point x0 as the initial value, and find the function value F(x0) corresponding to x0.

[0064] Step 33: Repeat steps 34 to 37 for the current x0.

[0065] Step 34: For the current solution x0, randomly perturb it to obtain a new solution x1.

[0066] Step 35: If F(x 1) Better than F(x0), then accept x1 and replace the initial value:

[0067] x0=x1, F(x0)=F(x1).

[0068] Step 36: If F(x 1) is not better than F(x0), then e Δf / kT Probability of accepting x1.

[0069] Δf=F(x1)-F(x0).

[0070] Step 37: If the termination condition is met, stop the loop and output the current solution x0 as the optimal solution.

[0071] Wherein: k is a constant coefficient less than 1, and the termination condition is usually taken as terminating the algorithm when several consecutive new solutions are not accepted; otherwise, the algorithm is returned to step 33 after decaying according to the decay function.

[0072] The simulated annealing algorithm is based on the similarity between solving the optimization problem and the annealing process of the physical system. It uses the Metropolis algorithm to appropriately control the temperature drop process to achieve simulated annealing.

[0073] The Metropolis algorithm is an algorithm based on random sampling, which is used to approximate the properties of physical systems in thermal equilibrium.

[0074] By constructing a Markov chain so that the stationary distribution of the chain is the same as the distribution you want to sample, the steps of this process are:

[0075] Step 12: Select an initial state: Randomly select an initial state from the possible state space.

[0076] Step 13: Generate a proposed state: Starting from the current state, generate a proposal for a new state based on the proposed distribution.

[0077] Step 14: Calculate the acceptance ratio: Determine whether to accept the proposal, which usually involves calculating the probability ratio of the current state and the proposed state.

[0078] Step 15: Decide whether to accept the proposal: Based on the acceptance ratio, randomly decide whether to accept the new state.

[0079] Step 16, Iteration: Repeat steps 13 to 15 until enough samples are obtained.

[0080] The density peak point is used as a reference for substitution, and the replaced ordinate ne / e is calculated through the abscissa time t and ordinate density ne of the peak point.

[0081] The 1 / e point positions corresponding to the peak points are obtained by interpolation method onto the density curve, and the time difference arrays of the compact ring plasma flying over the two fiber interferometers are obtained by the intervals corresponding to the two points.

[0082] Construct a polynomial function P(x) using the existing data, substitute the known y, and find the interpolated x.

[0083] The mathematical formula used in this process is:

[0084]

[0085] Calculate the average speed of the compact ring plasma to be measured flying over the two fiber interferometers, and use the time difference array and the position distance of the two fiber interferometers to calculate the average speed of the compact ring plasma to be measured according to the speed formula

[0086] The mathematical formula used in this process is:

[0087]

[0088] Where s is the position distance between the two fiber interferometers, and Δt is the calculated time difference array.

[0089] The present invention also provides a plasma velocity measurement system, referring to Figure 4 , the measurement system of this embodiment includes:

[0090] The measuring device 100 is used to measure the compact ring plasma to be measured based on the fiber interferometer, and obtain the curve of density signal data changing with the laser frequency;

[0091] The processing device 200 is used to calibrate the time starting point of the macroscopic velocity of the compact ring plasma. A gas plasma source of the same type is used as a reference source to measure the density signal of the compact ring plasma, and the time when the first complete peak appears is selected as the time starting point. The actual velocity distribution of the compact ring plasma to be measured is obtained by substitution based on the time starting point.

[0092] The measuring device 100 includes: a fiber laser 101 as an excitation light source, the output end of the laser 101 is connected to the optical path system, and the excitation light enters the compact ring host through the optical path system to interact with the particles; the measuring device 100 also includes: a fiber coupler 102 for splitting and combining optical signals, the fiber coupler 102 splits the laser into two laser beams with the same phase and amplitude; a fiber attenuator 103 for attenuating the optical power transmitted by the optical fiber to a certain extent, as well as a photodetector 104 for converting signals and a fiber collimator 105 for coupling the laser; a processor 106 for data acquisition, the processor 106 scans the laser frequency and records the density signal data detected by the photodetector 104 to obtain a curve of the density signal data changing with the laser frequency.

[0093] The processing device 200 comprises:

[0094] A first processing module 210 is used to perform data preprocessing on the two density signal data of the compact ring plasma by standardization and normalization;

[0095] A second processing module 220 is used to perform a peak search on the compact ring plasma density using a sliding window peak monitoring algorithm on the pre-processed data to obtain a peak value of a density signal;

[0096] The third processing module 230 is used to perform substitution based on the time when the first complete density peak appears, calculate the 1 / e point corresponding to the peak point through the corresponding peak point, and calculate the macroscopic speed by respectively obtaining the time difference value of the compact ring plasma to be measured flying through the two fiber interferometers through the intervals corresponding to the two points.

[0097] From the above description, it can be known that this embodiment is based on laser induction to measure plasma velocity. It measures the ion movement velocity by measuring the Doppler effect of the stimulated ions in the flow field to be measured. It is a non-contact measurement technology. There is no disturbance to the flow field to be measured, and it will not be affected by the widespread electrical and magnetic interference inside the compact ring device. It has high accuracy and strong anti-interference. Theoretically, as long as the laser-induced excitation strategy is reasonably selected, this scheme can measure the velocity of any particle, and it has no selectivity for whether the target particle is charged. It can realize off-site measurement, optical fiber transmission, and optical laboratory analysis, and has strong practical expansibility.

[0098] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for calculating the velocity of a compact ring plasma, characterized in that: The following steps are involved: Based on two fiber optic interferometers, density signal data of the compact ring plasma to be measured is measured, a plasma source of the same gas is used as a reference source, and the density signal data of the reference source is measured to obtain a curve of the change of the two plasma density signal data over time; Data preprocessing is performed on the obtained two plasma density signal data, and a peak search is performed on the density of the compact ring plasma to be measured through an algorithm, and the time at the density peak is selected as the starting point for calculating the velocity of the compact ring plasma to be measured; The density peak point is used as a reference for substitution, and the 1 / e point corresponding to the peak point is calculated through the corresponding peak point. The time difference array of the compact ring plasma to be measured flying through the two fiber interferometers is obtained through the intervals corresponding to the two points. The average speed of the compact ring plasma flying across the two fiber interferometers is obtained by using the time difference value and the distance between the two fiber interferometers according to the speed formula.

2. A method for calculating the velocity of a compact ring plasma according to claim 1, characterized in that: The specific method for measuring the plasma density is as follows: a laser is used as an excitation light source, and a 1×2 beam splitter is used to divide the light source into two beams; one beam is used as a reference beam, and the other beam is used as a detection beam. Two fiber optic collimators are used as transmitters and receivers to measure the change in the optical path of the electromagnetic wave passing through the plasma, thereby calculating the plasma density.

3. A method for calculating the velocity of a compact ring plasma according to claim 1, characterized in that: The obtained two plasma density signal data are preprocessed into standardization and normalization data preprocessing; The peak search algorithm for the density of the compact ring plasma to be measured is to use a sliding window peak monitoring algorithm to obtain the peak value of the density signal; The time when the first complete density peak appears is taken as the starting point of the compact ring plasma velocity.

4. A method for calculating the velocity of a compact ring plasma according to claim 3, characterized in that: The two density signal data are standardized and normalized. The mathematical formula of the algorithm used in this process is: Among them, x is the data after standardized calculation, x i is the original density signal collected by the fiber interferometer, μ is the original data mean, σ is the original data standard deviation, x′ is the normalized data, and x min is the minimum value of the data after normalization calculation, x max The maximum value of the data after normalization.

5. A method for calculating the velocity of a compact ring plasma according to claim 4, characterized in that: The specific method of substitution based on the density peak point is: the horizontal coordinate time t and the vertical coordinate density n of the peak point e , calculate the vertical coordinate n after substitution e / e, and substituted it onto the density curve by the interpolation method to obtain the 1 / e point position corresponding to the density peak point, and the time difference array of the compact ring plasma flying over the two fiber interferometers is obtained through the intervals corresponding to the two points.

6. A method for calculating the velocity of a compact ring plasma according to claim 5, characterized in that: The interpolation method is specifically as follows: construct a polynomial function P(x) through existing data, and substitute the known y into it to obtain the interpolated x. The mathematical formula used in this process is:

7. A method for calculating the velocity of a compact ring plasma according to claim 1, characterized in that: The specific method for calculating the average speed of the compact ring plasma to be measured flying over the two fiber interferometers is as follows: using the time difference array and the position distance of the two fiber interferometers, the average speed of the compact ring plasma to be measured is calculated according to the speed formula, and the speed formula is: Where s is the position distance between the two fiber interferometers, and Δt is the calculated time difference array.

8. A compact ring plasma velocity measurement system, characterized in that: include: A measuring device (100), which is used to measure the compact ring plasma to be measured based on a fiber interferometer, and obtain a curve of density signal data changing with laser frequency; A processing device (200) is used to calibrate the time starting point of the macroscopic velocity of a compact ring plasma, using a gas plasma source of the same type as a reference source, measuring the density signal of the compact ring plasma, selecting the time at which the first complete peak appears as the time starting point, and replacing the time starting point with the reference to obtain the actual velocity distribution of the compact ring plasma to be measured.

9. A compact ring plasma velocity measurement system according to claim 8, characterized in that: The measuring device (100) comprises: a fiber laser (101) as an excitation light source, the output end of the laser (101) is connected to an optical path system, and the excitation light enters the interior of the compact ring host through the optical path system to interact with particles; the measuring device (100) further comprises: a fiber coupler (102) for splitting and combining optical signals, the fiber coupler (102) splits the laser into two beams of laser light with the same phase and amplitude; a fiber attenuator (103) for attenuating the optical power of the optical fiber transmission to a certain degree, and a photodetector (104) for converting signals and for coupling the laser light into a fiber collimator (105); and a processor (106) for data acquisition, the processor (106) scanning the laser frequency and recording the density signal data detected by the photodetector (104) to obtain a curve of the density signal data changing with the laser frequency.

10. A compact ring plasma velocity measurement system according to claim 8, characterized in that: The processing device (200) comprises: A first processing module (210) is used to perform data preprocessing on the two density signal data of the compact ring plasma by standardization and normalization; A second processing module (220) is used to perform a peak search on the density of the compact ring plasma using a sliding window peak monitoring algorithm on the pre-processed data to obtain a peak value of a density signal; The third processing module (230) is used to perform substitution based on the time when the first complete density peak appears, calculate the 1 / e point corresponding to the peak point through the corresponding peak point, and calculate the macroscopic speed by respectively obtaining the time difference value of the compact ring plasma to be measured flying through the two fiber interferometers through the intervals corresponding to the two points.

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