A method for measuring heat flow of limiter under EAST long pulse low parameter discharge

Abstract

The application provides a limiter heat flow measurement method under EAST long pulse low parameter discharge, and belongs to the technical field of thermal load diagnosis of controlled nuclear fusion device, and comprises the following steps: obtaining measured heat flux data; setting electron temperature; obtaining heat flow decay length; realizing magnetic line tracing according to a three-dimensional model of the limiter and the first wall component and an experimental magnetic field file to obtain tracing results; obtaining magnetic connection results; setting heat flow decay width and heat flow value at the middle plane 2350 mm to simulate parallel heat flow distribution on the limiter surface; adjusting the maximum / minimum heat flow decay width to make the simulated heat flux trend consistent with the measured heat flux data; adjusting the boundary electron temperature at the middle plane 2350 mm to make the heat flow integral value of each column of tungsten blocks match the measured heat flux data; and outputting a three-dimensional heat flow distribution diagram of the limiter surface to realize the consistency of simulation and measurement. The application can obtain stable and reliable limiter heat flow spatial distribution results under low parameter working conditions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermal load diagnosis of controlled nuclear fusion devices, and particularly relates to a limiter heat flow measurement method under EAST long-pulse low-parameter discharge. BACKGROUND

[0002] In a tokamak nuclear fusion device, the limiter, as a first wall component directly in contact with the plasma boundary, bears extremely high thermal load. EAST (Experimental Advanced Superconducting Tokamak) is an important controlled nuclear fusion research platform, and its operation goal is to achieve high-parameter, long-pulse stable plasma. However, in experiments, it is observed that the limiter appears material ablation and metal droplet spatter under high heat flow, which eventually leads to plasma instability or discharge termination. At present, the heat flow distribution characteristics and formation mechanism of the EAST limiter surface are not clear, and the strong heat flow of the first wall has become a key bottleneck to limit the continuous operation of the stable discharge.

[0003] In the existing nuclear fusion device heat flow measurement, the commonly used technical means include:

[0004] Infrared thermal imaging system (IR): It has high time and spatial resolution, and is suitable for capturing the instantaneous response of heat flow; however, its measurement results depend on the material emissivity, surface conditions and other factors, and are easily affected by reflection and pollution, and there is an inversion error.

[0005] Langmuir probe: used to measure the boundary plasma parameters, and can estimate the heat flux; however, it has strong invasiveness, limited spatial coverage, and cannot be deployed on the main limiter for a long time.

[0006] Water-cooled calorimetric system: by monitoring the temperature difference and flow rate of the cooling water inlet and outlet, the average heat flow of the tungsten block is calculated, which has good anti-interference ability and energy closure. However, in the case of low heat flow (<10 kW / m 2 ), the resolution of the traditional water-cooled system is insufficient, and it is difficult to accurately obtain the thermal load data, especially in low-parameter long-pulse experiments.

[0007] In addition, the existing measurement methods mostly rely on a single means, and it is difficult to comprehensively obtain the quantitative values and spatial distribution characteristics of the limiter heat flow, and it is even more difficult to describe the dynamic change process with the evolution of the plasma. Therefore, a measurement method is needed, which is a multi-source data fusion combined with modeling simulation, can obtain stable and reliable limiter heat flow spatial distribution results under low-parameter working conditions, and provide support for plasma-wall interaction research. SUMMARY

[0008] To solve the above technical problems, the application provides an EAST long pulse low parameter discharge limiter heat flow measurement method, which can obtain stable and reliable limiter heat flow spatial distribution results under low parameter working conditions.

[0009] To achieve the above purpose, the application adopts the following technical scheme:

[0010] An EAST long pulse low parameter discharge limiter heat flow measurement method comprises the following steps:

[0011] The total heat flux of each column of tungsten blocks of the limiter is measured by a water-cooled calorimetric system to obtain measured heat flux data;

[0012] The microwave reflectometer is used to obtain the radial electron density distribution of the mid-plane, and the electron temperature is set in combination with the historical probe data;

[0013] According to the electron temperature, the parallel heat flow is exponentially fitted within the radial range of the limiter to obtain the heat flow decay length;

[0014] The magnetic field lines are tracked according to the three-dimensional model of the limiter and the first wall component and the experimental magnetic field file to obtain the tracking results;

[0015] The magnetic connection length of each grid of the three-dimensional model of the first wall component is calculated according to the tracking results to obtain the magnetic connection results;

[0016] According to the magnetic connection results, the heat flow decay width and the heat flow value at the 2350 mm of the mid-plane are set to simulate the parallel heat flow distribution on the surface of the limiter;

[0017] The maximum and minimum heat flow decay widths are determined according to the electron density decay width, and the maximum and minimum heat flow decay widths are adjusted to make the simulated heat flux trend consistent with the measured heat flux data;

[0018] The boundary electron temperature at the 2350 mm of the mid-plane is continuously adjusted to match the heat flow integral value of each column of tungsten blocks with the measured heat flux data;

[0019] The three-dimensional heat flow distribution map of the limiter surface is output to realize the simulation and the measured results.

[0020] Further, the thermocouple temperature measurement accuracy of the water-cooled calorimetric system is ±0.05 ℃, the data acquisition accuracy is not less than ±0.01 ℃, and the flow measurement accuracy is better than 5%.

[0021] Further, the microwave reflectometer measurement frequency range is 30 GHz to 110 GHz.

[0022] Further, the experimental magnetic field file is derived from the experimental real-time magnetic field data.

[0023] Further, the magnetic connection length of each grid of the first wall component three-dimensional model is calculated according to the tracking result, and a magnetic connection result is obtained, including: setting a maximum magnetic connection length, a step length, and a minimum magnetic connection length, and calculating the magnetic connection length of each grid according to the grid division of the first wall component three-dimensional model.

[0024] Further, the maximum and minimum heat flux decay widths are determined according to the electron density decay width, and the maximum and minimum heat flux decay widths are adjusted to make the simulated heat flux trend consistent with the measured heat flux data, including: continuously adjusting the heat flux decay width within the range of the maximum and minimum heat flux decay widths until the trend is consistent.

[0025] Further, the boundary electron temperature at the middle plane 2350 mm is continuously adjusted to make the heat flux integral value of each column match the measured heat flux data, including: adjusting the boundary electron temperature at the middle plane 2350 mm by iteration to make the difference between the heat flux integral of each column and the measured value less than a set threshold.

[0026] Further, the output three-dimensional heat flux distribution map is in the form of a three-dimensional color cloud map.

[0027] Further, a plurality of simulations are performed based on the maximum / minimum electron density decay width to evaluate the sensitivity of the heat flux distribution to the decay width.

[0028] Further, all steps are completed under non-invasive conditions without disturbing the plasma discharge.

[0029] Advantages:

[0030] 1. The present application can clearly distinguish kW / m 2 Low heat flux, suitable for low parameter and long pulse working conditions;

[0031] 2. The present application realizes double closure of heat flux trend and value, improving the diagnosis accuracy;

[0032] 3. The present application uses a non-invasive method to avoid disturbing the plasma;

[0033] 4. The present application can be extended to other tokamak devices;

[0034] 5. The microwave reflectometer of the present application can be used as a conventional diagnostic method for EAST, and can be used for a long time, and the data is comprehensive;

[0035] 6. The present application is suitable for discharge flat top segment heat load measurement, and can also be extended to heat load evolution analysis through thermodynamic simulation;

[0036] 7. The present application can be used for limiter structure layout optimization, cooling design verification, and material heat load tolerance research;

[0037] 8. The present application provides feedback input for SOL (Scrape-Off Layer) area transport modeling by measuring the scrape-off layer plasma parameters. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1a A schematic diagram of the limiter structure;

[0039] Figure 1b A schematic diagram of the water-cooled calorimetric system;

[0040] Figure 2 An electron density profile measured by a microwave reflectometer;

[0041] Figure 3 A flow chart of a limiter heat flux measurement method under EAST long-pulse low-parameter discharge according to the present application;

[0042] Figure 4a A schematic diagram of the heat flux distribution result simulated according to the present application;

[0043] Figure 4b A comparison diagram of 7-column heat flux simulation and measurement results. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be 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 used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0045] The present application provides a limiter heat flux measurement method under EAST long-pulse low-parameter discharge, which is suitable for EAST main limiter heat flux distribution measurement under low-parameter and long-pulse discharge conditions. By combining a water-cooled calorimetric system, boundary plasma parameter diagnosis and PFC FLUX simulation modeling, trend matching and numerical fitting of limiter heat load are realized, and heat flux spatial distribution is obtained.

[0046] As shown in Figure 1a , Figure 1b The limiter according to the present application includes seven columns of tungsten strings (including pipes and heat sinks) in total, each column of tungsten string is formed by mounting 77 independent tungsten blocks on an independent through copper pipe, the 77 independent tungsten blocks form a tungsten string, and the tungsten string and the through copper pipe are connected by a heat sink. Figure 1bThe area within the dashed line represents the limiter. The water-cooled calorimeter system includes an inlet thermometer, an outlet thermometer, and a flow meter installed on a through-tube copper pipe outside the EAST device. That is, the water pipe (i.e., the through-tube copper pipe) of the limiter is very long and can extend outside the EAST device. The inlet and outlet thermometers and the flow meter are installed at suitable locations outside the EAST device. "Suitable" refers to a location that is as close as possible to the limiter, has sufficient construction space, and allows for the installation of measuring instruments.

[0047] Specifically, such as Figure 3 As shown, the method for measuring limiter heat flux under EAST long-pulse low-parameter discharge according to the present invention includes the following steps:

[0048] Step 1: Obtain the measured values, including:

[0049] The total heat flux of tungsten blocks in different columns of the limiter of the EAST device was measured using a water-cooled calorimetric system. It should be noted that the water-cooled calorimetric system measures the heat flux, which is the measured value.

[0050] Step 2: Set the electronic temperature, including:

[0051] The radial electron density distribution in the mid-plane (referring to the horizontal plane centered in the vertical direction of EAST) was obtained using a microwave reflectometer. Combined with historical probe data, an electron temperature was assumed (the limiter is located far from the SOL layer, so the electron temperature can be considered constant; here, the electron temperature can be considered equal to the ion temperature, and the electron density equal to the ion density). For example... Figure 2 As shown, the horizontal axis represents the radial distance R (in meters), and the vertical axis represents the electron density n. e (Unit is) / ), 156805 is the gun number, and @10s indicates that the data was measured at 10 seconds. The maximum value is the decay width of the fitted electron density when the error bars are not considered. To account for the minimum when considering error bars (where max represents a fast decay rate, not necessarily a specific value). The decay width (max) is the fitted electron density, where max indicates a fast decay rate and min indicates a slow decay rate. Error bars are line segments or bar areas used in experimental data visualization to represent measurement uncertainty; they typically appear at each data point in a chart.

[0052] Step 3: Obtain the heat flux decay length, including:

[0053] Calculate the parallel heat flow in the limiter region, and fit an exponential function to the heat flow distribution within the radial range of the limiter (R=2350mm to R=2370mm) to obtain the heat flow attenuation length λ.

[0054] ;

[0055] ;

[0056] ;

[0057] where, is the total parallel heat flux density at the entrance of the sheath, is the contribution of ions to the sheath heat flux, is the contribution of electrons to the sheath heat flux, is the sheath heat flux coefficient (empirical value, typically 7-8), k is the Boltzmann constant, is the electron temperature, is the ion temperature, is the particle flux density at the entrance of the sheath, is the plasma density at the entrance of the sheath, is the particle velocity at the entrance of the sheath, is the ion sound speed, defined as , is the background plasma density in the extended plasma region (e.g. SOL), is the ion mass.

[0058] Step 4, magnetic field line tracing, including:

[0059] Import the limiter (as the analyzed component) and other first wall components 3D models (as magnetic shielding components) and magnetic field files in PFC FLUX simulation software (which is a general software in the field of plasma), and perform magnetic field line tracing;

[0060] Step 5, obtain the magnetic shielding and magnetic connection results through magnetic field line tracing, including:

[0061] Set the maximum magnetic connection length, step size and minimum magnetic connection length, and start analysis. PFC FLUX simulation software calculates the magnetic connection length of each grid according to the grid division of the 3D model, that is, the magnetic connection result. This process can be understood as follows: first find a grid of the limiter, then according to the magnetic field file, let its magnetic field lines extend to the left and right until other first wall components or reach the set value of the maximum magnetic connection length, at this time the length of the left plus the right is the magnetic connection length.

[0062] Step 6, simulate heat flux distribution, including:

[0063] According to the magnetic communication result of step 5, on this basis, the heat flow calculation module of the PFC FLUX simulation software is opened, the heat flow attenuation width and the heat flow at the middle plane 2350mm (the heat flow here is calculated according to the initial assumed electron temperature) are set, and then the simulation calculation is started, and the limiter surface parallel heat flow is preliminarily obtained. It needs to be clear that the PFC FLUX simulation software simulates the heat flow distribution, and the heat flux is obtained by multiplying the area and then integrating the column.

[0064] Step 7, make the simulation results consistent with the measured heat flux trend, including:

[0065] According to the maximum and minimum electron density attenuation width, the maximum and minimum heat flow attenuation width is calculated, and the heat flow attenuation width is adjusted in the maximum and minimum heat flow attenuation width range, so that the simulation results are consistent with the measured heat flux trend;

[0066] Step 8, calculate the heat flow of the limiter, including:

[0067] Further adjust the boundary electron temperature value, because the closest distance to the plasma on the middle plane is 2350mm, so calculate the parallel heat flow at the middle plane 2350mm, so that the integral of each column heat flow distribution (i.e. heat flux) matches the measured value. It needs to be clear that the heat flow of the whole limiter is calculated according to the heat flow value at the middle plane 2350mm, the magnetic field tracking result and the heat flow attenuation width.

[0068] Step 9, output the heat flow distribution diagram of the limiter surface, realize simulation-measured closed.

[0069] Specifically, the temperature measurement accuracy of the water-cooled calorimetric system thermocouple is ±0.05℃, the data acquisition accuracy is not less than ±0.01℃, and the flow measurement accuracy is better than 5%.

[0070] Specifically, the microwave reflectometer measurement frequency range is 30GHz to 110GHz.

[0071] Specifically, the magnetic field file used by the PFC FLUX simulation software is derived from the experimental magnetic field data.

[0072] Specifically, the initial setting of the boundary electron temperature refers to the existing probe measurement data of similar discharges.

[0073] Specifically, the output heat flow distribution is a three-dimensional image, which represents the heat flow of the limiter surface changing with space.

[0074] Specifically, a plurality of simulations are performed according to maximum and minimum electron density decay widths to analyze simulation sensitivity. When the decay width changes, the proportion of heat flux of different columns will change, so the maximum and minimum heat flow decay widths are calculated according to the maximum and minimum electron density decay widths, and then input into the PFC FLUX software. When the proportion of heat flux of different columns changes greatly, the sensitivity is high, and vice versa, the sensitivity is low.

[0075] Embodiments:

[0076] Taking EAST typical low parameter discharge #156805 as an example, it is a pure ECRH (electron cyclotron resonance heating) discharge, low power, L mode, the boundary electron temperature and the ion temperature can be regarded as the same, the electron density and the ion density can be regarded as the same, and the plasma can be regarded as running along the magnetic field line. As shown in FIG. 1, the water-cooled calorimetric system measures the heat flux of 7 columns of tungsten blocks (R1-R7 from right to left), the microwave reflectometer data are fitted to the boundary electron density, the magnetic field is introduced into the PFC FLUX simulation software to simulate the heat flow. By adjusting the parameters, the trend and the numerical value are closed, and the complete heat flow distribution diagram is output. Among them, Figure 4a Figure 4b is a heat flow distribution result diagram simulated by the present application; Figure 4a is a comparison diagram of 7-column heat flux simulation and actual measurement results. Figure 4b

[0077] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.​​

Claims

1. A method for measuring heat flux of a limiter in EAST long-pulse low-parameter discharge, characterized in that, The method comprises the following steps: The total heat flux of each column of tungsten blocks of the limiter is measured respectively to obtain measured heat flux data; The radial electron density distribution of the mid-plane is obtained by using a microwave reflectometer, and the electron temperature is set in combination with historical probe data; According to the electron temperature, the parallel heat flux is exponentially fitted within the radial range of the limiter to obtain the heat flux decay length; The magnetic field tracing is performed according to the three-dimensional model of the limiter and the first wall component and the experimental magnetic field file to obtain the tracing result; The magnetic connection length of each grid of the three-dimensional model of the first wall component is calculated according to the tracing result to obtain the magnetic connection result; According to the magnetic connection result, the heat flux decay width and the heat flux value at the mid-plane of 2350 mm are set to simulate the parallel heat flux distribution on the surface of the limiter; According to the electron density decay width, the maximum heat flux decay width and the minimum heat flux decay width are determined, and the maximum heat flux decay width and the minimum heat flux decay width are adjusted to make the simulated heat flux trend consistent with the measured heat flux data; The boundary electron temperature at the mid-plane of 2350 mm is continuously adjusted to make the heat flux integral value of each column of tungsten blocks match the measured heat flux data; A three-dimensional heat flux distribution map of the limiter surface is output to realize the consistency between simulation and measurement.

2. The EAST long-pulse low-parameter discharge limiter thermal flux measurement method according to claim 1, characterized in that, The total heat flux of each column of tungsten blocks of the limiter is measured by a water-cooled calorimetric system; the water-cooled calorimetric system comprises an inlet thermometer, an outlet thermometer and a flowmeter installed on a through copper pipe outside the EAST device; the thermocouple temperature measurement accuracy of the inlet thermometer and the outlet thermometer of the water-cooled calorimetric system is ±0.05 ℃, the data acquisition accuracy is not less than ±0.01 ℃, and the flow measurement accuracy is better than 5%.

3. The EAST long-pulse low-parameter discharge limiter thermal flux measurement method according to claim 1, characterized in that, The frequency range measured by the microwave reflectometer is 30 GHz to 110 GHz.

4. The EAST long-pulse low-parameter discharge limiter thermal flux measurement method of claim 1, wherein, The experimental magnetic field file is derived from the experimental real-time magnetic field data.

5. The EAST long-pulse low-parameter discharge limiter thermal flux measurement method according to claim 1, wherein, The magnetic connection length of each grid of the three-dimensional model of the first wall component is calculated according to the tracing result to obtain the magnetic connection result, which comprises: setting the maximum magnetic connection length, the step length and the minimum magnetic connection length, calculating the magnetic connection length of each grid according to the grid division of the three-dimensional model of the first wall component, and obtaining the magnetic connection result.

6. The EAST long-pulse low-parameter discharge limiter thermal flux measurement method according to claim 1, wherein, According to the electron density decay width, the maximum heat flux decay width and the minimum heat flux decay width are determined, and the maximum heat flux decay width and the minimum heat flux decay width are adjusted to make the simulated heat flux trend consistent with the measured heat flux data, which comprises: continuously adjusting the heat flux decay width within the range of the maximum heat flux decay width and the minimum heat flux decay width until the trend is consistent.

7. The EAST long-pulse low-parameter discharge limiter thermal flux measurement method according to claim 1, wherein, The boundary electron temperature at the mid-plane of 2350 mm is continuously adjusted to make the heat flux integral value of each column of tungsten blocks match the measured heat flux data, which comprises: iteratively adjusting the boundary electron temperature at the mid-plane of 2350 mm to make the difference between the heat flux integral of each column and the measured value less than a threshold value.

8. The EAST long-pulse low-parameter discharge limiter thermal flux measurement method of claim 1, wherein, The output three-dimensional heat flux distribution map is in the form of a three-dimensional color cloud map.

9. The EAST long-pulse low-parameter discharge limiter thermal flux measurement method according to claim 1, wherein, The method comprises: performing multiple groups of simulation based on the maximum electron density decay width and the minimum electron density decay width to evaluate the sensitivity of the heat flux distribution to the decay width.

10. The EAST long-pulse low-parameter discharge limiter thermal flux measurement method of claim 1, wherein, All steps are completed under non-invasive conditions without interfering with the plasma discharge.

Images