A compact toroid plasma velocity calculation method and measurement system

Abstract

The application discloses a compact ring plasma velocity calculation method and a measuring system, and relates to the technical field of plasma diagnosis, and 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; performing peak value search on the density of the to-be-measured compact ring plasma through an algorithm, selecting the time at the density peak value as an initial point of the velocity of the to-be-measured compact ring plasma; obtaining a time difference array of the to-be-measured compact ring plasma flying through the two optical fiber interferometers through the intervals corresponding to the two points respectively; and obtaining the average velocity of the to-be-measured compact ring plasma by using the time difference array and the distance of the two optical fiber interferometers. The application measures the velocity of the plasma based on the density signal of the optical fiber interferometer, measures the movement velocity of the plasma through the time difference of the to-be-measured plasma flying through the two optical fiber interferometers, and obtains a more accurate density initial point interval through the algorithm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of plasma diagnosis, and particularly relates to a compact toroid plasma velocity calculation method and a measuring system. BACKGROUND

[0002] The compact toroid injection system is a technology for core feeding of a fusion device, and has the characteristics of being capable of striking a high-speed and high-density self-organizing plasma group. In a magnetic confinement fusion experimental device, the compact toroid injection system is the most promising scheme for realizing core feeding on a large tokamak. Using the compact toroid injection plasma to enter the tokamak needs to make the compact toroid plasma pass through an external strong magnetic field to enter the core of the fusion reactor. When the compact toroid plasma passes through the gradient magnetic field, a very high speed is needed to reach the condition of core feeding. Therefore, it is particularly important to study whether the compact toroid plasma velocity can meet the condition of passing through the gradient magnetic field.

[0003] The method for calculating the macroscopic velocity of the high-temperature plasma is still a technology that needs to be further improved. The existing method such as the magnetic probe measurement has a large error in the measurement result under the condition that the magnetic field is strong, because the measurement accuracy of the magnetic probe is affected by the magnetic field. In the compact toroid injection system, the influence of the magnetic field is often not negligible. Therefore, it is necessary to develop a new type of compact toroid plasma velocity calculation method SUMMARY

[0004] The present application relates to the technical field of plasma diagnosis, and particularly relates to a compact toroid plasma velocity calculation method and a measuring system.

[0005] The technical problems can be solved by the following technical solutions.

[0006] A compact toroid plasma velocity calculation method comprises the following steps:

[0007] Based on two optical fiber interferometer measurement of the compact toroid plasma density signal data to be measured, an equal gas plasma source is used as a reference source to measure the density signal data of the reference source, and two plasma density signal data curves changing with time are obtained.

[0008] The obtained two plasma density signal data are preprocessed, and the peak value of the compact toroid plasma density to be measured is searched through an algorithm, and the time at the density peak value is selected as the starting point of the compact toroid plasma velocity 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 based on the speed formula using the time difference value and the distance between the two fiber interferometers.

[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, using a 1×2 beam splitter to split 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 compact ring plasma density 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, the two density signal data are standardized and normalized. 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 mean of the original data, σ is the standard deviation of the original data, x′ is the data after normalization calculation, and x min is the minimum value of the data after normalization calculation, x max The maximum value of the data after normalization calculation.

[0018] As a further solution of the present invention: the density peak point is used as the 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 through the two fiber optic interferometers is obtained through the intervals corresponding to the two points.

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

[0020]

[0021] As a further scheme of the present application: the specific method for calculating the average speed of the to-be-measured compact ring plasma passing through two fiber interferometers is: using the time difference array and the position distance of the two fiber interferometers, and according to a speed formula, the average speed of the to-be-measured compact ring plasma is obtained, and the speed formula is:

[0022]

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

[0024] As a further scheme of the present application: a compact ring plasma speed measurement system comprises:

[0025] A measuring device for measuring the to-be-measured compact ring plasma based on fiber interferometer measurement, and measuring a density signal data curve varying with laser frequency;

[0026] A processing device for calibrating a time starting point of a macroscopic speed of the compact ring plasma, taking a same gas plasma source as a reference source, measuring the density signal of the compact ring plasma, selecting a time at which a first complete peak appears as the time starting point, and performing substitution based on the time starting point to obtain an actual speed distribution of the to-be-measured compact ring plasma.

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

[0028] As a further scheme of the present application: the processing device comprises:

[0029] The first processing module is used for data pretreatment of the compact ring plasma two-channel density signal data through standardization and normalization.

[0030] The second processing module is used for peak value search of the compact ring plasma density by using a sliding window peak value monitoring algorithm on the pretreated data, so as to obtain a peak value of the density signal.

[0031] The third processing module is used for substitution based on a time at which a first complete density peak value appears, calculation of an / e point corresponding to the peak value point, and calculation of a macroscopic velocity by using a time difference value of the to-be-measured compact ring plasma flying through two optical fiber interferometers.

[0032] The present application has the advantages that the present application measures the plasma velocity based on the density signal of the optical fiber interferometer, measures the plasma movement velocity by using the time difference of the to-be-measured plasma flying through two optical fiber interferometers, and obtains a more accurate density starting point interval by using an algorithm, is a new measurement technology, is not affected by electric and magnetic interference, has the advantages of high precision, strong anti-interference performance, and wide applicability, and can be widely applied. BRIEF DESCRIPTION OF DRAWINGS

[0033] The present application will be further described below in combination with the drawings.

[0034] Figure 1 An implementation process schematic diagram of the plasma velocity calculation method provided for the embodiment of the present application is provided.

[0035] Figure 2 A position schematic diagram of the optical fiber interferometer used for collecting the density on the compact ring injection device mentioned for the embodiment of the present application is provided.

[0036] In the drawing, 1 is a first window of the optical fiber interferometer, 2 is a second window of the optical fiber interferometer, and 3 is a third window of the optical fiber interferometer.

[0037] Figure 3 An implementation flowchart of the plasma velocity calculation method provided for the embodiment of the present application is provided.

[0038] Figure 4 A structure schematic diagram of the plasma velocity measurement system provided for the embodiment of the present application is provided.

[0039] Figure 5 A structure schematic diagram of the measurement device in the plasma velocity measurement system provided for the embodiment of the present application is provided.

[0040] Figure 6 A velocity calculation interval selected on the density signal provided for the embodiment of the present application is provided.

[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 torus plasma velocity calculation method provided by the present application is described in detail below. The contents not described in detail in the embodiments of the present application belong to the prior art known to those skilled in the art. If the specific conditions are not specified in the embodiments of the present application, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used in the embodiments of the present application are not specified by the manufacturer, they are all conventional products that can be purchased on the market. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0043] Specifically, referring to Figures 1-6 As shown in the figure, the present application proposes a compact torus plasma velocity calculation method based on sliding window and simulated annealing algorithm for calculating the velocity of compact torus plasma. The method can be used to intercept the compact torus plasma density interval to calculate the time of flying through two fiber interferometer windows, so as to calculate the velocity of the compact torus plasma.

[0044] The basic processing flow involved in the compact torus plasma velocity calculation method provided by the embodiments of the present application is as shown in Figure 1 Specifically, the method comprises the following steps:

[0045] Step S1: collecting the density signal of the compact torus plasma, wherein the density signal comprises the density signals collected from Figure 2 the first fiber interferometer window and the third fiber interferometer window, wherein the three groups of windows of the fiber interferometer are used to check the collected signal data, and the two fiber interferometers are distributed at different windows to realize the calculation of different spacings.

[0046] Specifically, the compact torus plasma density collection uses a homodyne Mach-Zehnder laser interferometer, which mainly consists of a fiber laser, a fiber coupler, a fiber attenuator, a wavelength division multiplexer, a collimator and a photodetector.

[0047] A 1kHz, 1550nm ultra-narrow linewidth laser is used as the excitation light source, and a 1x2 beam splitter is used to divide the light source into two beams: one as a reference beam and the other as a probe beam. Two fiber collimators are used as emitters and receivers, which are located on both sides of the plasma 1.

[0048] Reference beam and probe beam are sent into two input ends of 3*3 coupler, leaving one input end empty, in order to avoid the echo of laser, the empty input end is covered with a light shield cap, three output ends are connected to photodetectors.

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

[0050] Step S2: the density signal data is processed into two density signal data, which includes data standardization and normalization;

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

[0052]

[0053] Wherein, 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 compact toroid plasma density to be measured is a sliding window peak monitoring algorithm, and the peak value of the density signal is obtained.

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

[0056] The sliding window algorithm is used to search for the peak value of the compact toroid plasma density, a window size is defined, and the peak value is searched in each window, and the specific steps are as follows:

[0057] Step 1, define a window size, which represents the range of peak value to be detected in time series.

[0058] Step 2, start 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 value in the current window is less than or equal to 80% of the maximum value of the whole data set, adjust the window size to better adapt to the smaller amplitude peak value.

[0062] Step 31: use the simulated annealing algorithm to search for the peak value of the compact toroid plasma density, which can include the following steps:

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

[0064] Step 33: For the current x0, repeat steps 34-37.

[0065] Step 34: Randomly perturb the current solution x0 to get a new solution x1.

[0066] Step 35: If F(x 1) is better than F(x0), 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), accept x1 with probability e Δf / kT

[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] where k is a constant less than 1, and the termination condition is usually set to terminate the algorithm when a certain number of new solutions are not accepted; otherwise, return to step 33 after decay.

[0072] Simulated annealing algorithm is based on the similarity between the solution of optimization problems and the annealing process of physical systems, and uses the Metropolis algorithm to appropriately control the temperature drop to achieve simulated annealing.

[0073] The Metropolis algorithm is a random sampling-based algorithm used to approximate the properties of a physical system in thermal equilibrium.

[0074] By constructing a Markov chain whose stationary distribution is the same as the distribution to be sampled, the steps of this process are:

[0075] Step 12, Choose an initial state: randomly choose an initial state from the possible state space.

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

[0077] Step 14, Calculate the acceptance ratio: determine whether to accept this 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 this new state.​

[0079] Step 16, iteration: repeat steps 13-15 until enough samples are obtained.

[0080] The abscissa time t and the ordinate density ne of the peak point are substituted to calculate the ordinate ne / e after substitution.

[0081] The 1 / e point position corresponding to the peak point is obtained by interpolation method to the density curve, and the time difference array of the compact ring plasma flying through the two fiber interferometers is obtained by the interval corresponding to the two points.

[0082] The polynomial function P(x) is constructed by the existing data, and the known y is substituted to obtain the interpolated x.

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

[0084]

[0085] The average speed of the compact ring plasma to be measured flying through the two fiber interferometers is calculated, the position distance of the two fiber interferometers is used, and the average speed of the compact ring plasma to be measured is calculated according to the speed formula

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

[0087]

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

[0089] The application also provides a plasma speed measurement system, referring to Figure 4 , the measurement system of the embodiment comprises:

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

[0091] The processing device 200 is used for calibrating the time starting point of the macroscopic speed of the compact ring plasma, taking the same gas plasma source as the reference source, measuring the density signal of the compact ring plasma, selecting the time when the first complete peak appears as the time starting point, and substituting the time starting point to obtain the actual speed distribution of the compact ring plasma to be measured.

[0092] The measuring device 100 comprises: a fiber laser 101 as an excitation light source, the output end of the laser 101 is connected with an optical path system, excitation light enters the inside of a compact ring host through the optical path system and interacts 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 the same phase and the same amplitude; a fiber attenuator 103 for attenuating the optical power transmitted by the optical fiber to a certain degree, and a photodetector 104 for converting signals and a fiber collimator 105 for coupling 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 the curve of the density signal data changing with the laser frequency.

[0093] The processing device 200 comprises:

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

[0095] A second processing module 220 is configured to perform peak search on the compact ring plasma density by using a sliding window peak monitoring algorithm on the preprocessed data, to obtain the peak value of the density signal.

[0096] A third processing module 230 is configured to take the time when the first complete density peak appears as a reference, calculate the 1 / e point corresponding to the peak point, and obtain the time difference value of the compact ring plasma passing through the two-channel fiber interferometer to calculate the macroscopic velocity.

[0097] From the above description, it can be seen that the embodiment is based on laser-induced plasma velocity measurement, which measures the ion motion velocity by measuring the Doppler effect of the ion excited by the laser, is a non-contact measurement technology, does not disturb the measured flow field, and is not affected by the wide existence of electric and magnetic interference in the compact ring device, has high precision and strong anti-interference performance. In theory, as long as the excitation strategy of the laser induction is reasonably selected, the scheme can measure the velocity of any particle, and has no selectivity for whether the target particle is charged, can realize remote measurement, fiber transmission and optical laboratory analysis, and has strong practical expandability.

[0098] The above describes one embodiment of the present application in detail, but the content is only the preferred embodiment of the present application, and cannot be considered as limiting the scope of the present application. Any equivalent changes and improvements made within the scope of the present application should still belong to the patent coverage of the present application.

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, the density signal data of the compact ring plasma to be measured is measured, and a plasma source of the same gas is used as a reference source. 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 two obtained plasma density signal data, and a peak search is performed on the density of the compact ring plasma to be measured using 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 velocity of the compact ring plasma flying across the two fiber interferometers is obtained based on the velocity formula using the time difference value and the distance between the two fiber interferometers. The obtained two plasma density signal data are preprocessed into standardization and normalization data preprocessing; The peak search algorithm for the compact ring plasma density 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.

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 to be measured is: using a laser as the excitation light source, and using a 1×2 beam splitter to split the light source into two beams; one beam is used as a reference beam and the other 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. The method for calculating the velocity of a compact ring plasma according to claim 1, wherein: The two density signal data are standardized and normalized. The mathematical formula of the algorithm used in this process is: ， in, The data after normalization calculation is is the original density signal collected by the fiber interferometer, μ is the mean value of the original data, σ is the standard deviation of the original data, is the data after normalization calculation, is the minimum value of the data after normalization calculation, The maximum value of the data after normalization calculation.

4. A method for calculating the velocity of a compact ring plasma according to claim 3, 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 through the two fiber optic interferometers is obtained through the intervals corresponding to the two points.

5. A method for calculating the velocity of a compact ring plasma according to claim 4, characterized in that: The interpolation method is specifically as follows: construct a polynomial function P(x) using the existing data, and substitute the known y into it to find the interpolated x. The mathematical formula used in this process is: ; 。 6. The method for calculating the velocity of a compact ring plasma according to claim 1, wherein: The specific method for calculating the average velocity of the compact ring plasma to be measured flying through the two fiber optic interferometers is as follows: using the time difference array and the position distance between the two fiber optic interferometers, the average velocity of the compact ring plasma to be measured is calculated according to the velocity formula, which is: Where s is the distance between the two fiber interferometers. t is the calculated time difference array.

7. A measurement system for the compact ring plasma velocity calculation method according to any one of claims 1 to 6, characterized in that: include: A measuring device (100) 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 performing substitution based on the time starting point to obtain the actual velocity distribution of the compact ring plasma to be measured.

8. The compact ring plasma velocity measurement system according to claim 7, characterized in that: The measuring device (100) comprises: a fiber laser (101) as an excitation light source, wherein 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, wherein 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 transmitted by the optical fiber to a certain extent, a photodetector (104) for converting signals, and a fiber collimator (105) for coupling the laser light into the optical fiber; and a processor (106) for data acquisition, wherein 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.

9. The compact ring plasma velocity measurement system according to claim 7, 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 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; The third processing module (230) is used to perform substitution based on the time at which 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 velocity by respectively obtaining the time difference value of the compact ring plasma to be measured flying through the two fiber optic interferometers through the intervals corresponding to the two points.

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