Plasma ion three-dimensional flow velocity distribution detection system and method

Abstract

The invention discloses a plasma ion three-dimensional flow velocity distribution detection system and method, and belongs to the technical field of plasma diagnosis. The system comprises a Mach probe, a controllable voltage source, a sampling resistor and a voltage acquisition system, the Mach probe, the sampling resistor and the controllable voltage source are connected in series through wires to form a loop, and the voltage acquisition system is connected in parallel with the controllable voltage source and the sampling resistor and is used for acquiring the voltage of the controllable voltage source and the sampling resistor. According to the detection method, on the basis of the multi-axis vector synthesis principle, ion flow velocity components in different planes are obtained by inserting a Mach probe in the three-axis direction, and a three-dimensional flow velocity component is calculated through a vector synthesis algorithm. According to the invention, the local flow field structure in the ion source can be diagnosed, the spatial distribution characteristic of the ion flow velocity can be revealed, the spatial resolution is high, the velocity information of particles can be directly provided, the three-dimensional data of the ion flow velocity measurement can be synthesized without complex optical path rotation or multiple scanning, and the experimental device is simple and low in cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of plasma diagnostics, and particularly relates to a plasma ion three-dimensional flow velocity distribution detection system and method. Background Art

[0002] In a neutral beam injection system, an ion source, as a core component, is responsible for generating high-energy and high-density ion beams, providing a basic guarantee for the generation and injection of neutral beams. Among them, the three-dimensional spatial distribution characteristics of the ion flow velocity of the ion source are the core parameters characterizing the working state of the ion source. The spatial distribution characteristics of the ion flow velocity can reflect the flow characteristics of the plasma inside the ion source, which are crucial for adjusting the collimation and uniformity of the ion beam, and thus promoting the improvement of the energy utilization efficiency of the neutral beam. In addition, the measurement of the ion flow velocity also provides an experimental basis for the verification of numerical simulations and theoretical models, and provides a guiding basis for further optimizing the design and operating parameters of the ion source.

[0003] At present, there are few measurement methods for the ion flow velocity of the ion source in the neutral beam injection system, mainly including: First, a retarding field energy analyzer indirectly deduces the ion flow velocity by measuring the energy distribution of ions in a retarding electric field. This method has a complex experimental device, limited spatial resolution, and cannot directly provide the velocity information of particles; Second, the laser-induced fluorescence method uses a laser with a specific wavelength to excite ion transitions, measures the velocity component of ions along the laser beam direction through the Doppler frequency shift, and combines scanning or spectroscopy to achieve two-dimensional ion flow velocity mapping. This method can only obtain the velocity component in a single direction in a single measurement, and complex optical path rotation or multiple scans are required to synthesize the three-dimensional data of the ion flow velocity measurement. Summary of the Invention

[0004] To solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A plasma ion three-dimensional flow velocity distribution detection system includes: a Mach probe, as well as a controllable voltage source, a sampling resistor, and a voltage acquisition system; the Mach probe, the sampling resistor, and the controllable voltage source are connected in series through wires to form a loop, and the voltage acquisition system is connected in parallel to the controllable voltage source and the sampling resistor for collecting the voltages of the controllable voltage source and the sampling resistor.

[0006] A plasma ion three-dimensional flow velocity distribution detection method, based on the above-mentioned plasma ion three-dimensional flow velocity distribution detection system, includes:

[0007] Step 1: Insert the Mach probe along a certain direction, such as the y-axis direction, into the plasma cavity of the ion source, and adjust the center position of the collection electrode of the Mach probe to the detection point.

[0008] Step 2: Rotate the Mach probe so that the center connection line of the first pair of opposite electrodes is parallel to the x-axis and the center connection line of the second pair of opposite electrodes is parallel to the z-axis.

[0009] Step 3: Connect the output terminals of the controllable voltage source to the four collection electrodes of the Mach probe through four independent sampling resistors respectively, and connect the common terminal of the controllable voltage source to the ion source housing to form a closed current loop;

[0010] Step 4: Use the voltage acquisition system to synchronously collect the voltages across the controllable voltage source and the four sampling resistors, and take the difference to obtain the voltage values of the four collection electrodes;

[0011] Step 5: Calculate the current values of each electrode according to Ohm's law, and draw the I-V curve of each collection electrode based on the experimental data of the voltage and current of each collection electrode;

[0012] Step 6: Extract the saturated ion current and electron temperature from the I-V curve obtained from each collection electrode, and calculate the ion flow velocity components in the x-z plane at the detection point by combining the ion flow velocity calculation theory , ;

[0013] Step 7: Keep the detection point position unchanged, insert the Mach probe along the x-axis direction, and repeat Steps 2-6 to measure the ion flow velocity components in the y-z plane at the detection point , ; And, keep the detection point position unchanged, insert the Mach probe along the z-axis direction, and repeat Steps 2-6 again to measure the ion flow velocity components in the x-y plane at the detection point , ;

[0014] Step 8: Adopt the vector synthesis algorithm: , and calculate the flow direction angles , through the direction cosines to obtain the three-dimensional flow velocity of the plasma at the detection point;

[0015] Step 9: Change the spatial coordinates of the detection point at equal intervals, and loop through Steps 1 to 8 to perform spatial grid scanning measurements to obtain the three-dimensional flow velocity distribution characteristics of the plasma.

[0016] The present invention has the following beneficial effects:

[0017] The system of the present invention uses a tungsten rod with a high electron work function as the ion collection electrode, and cooperates with a precision-machined alumina ceramic insulating material to control the outer diameter of the Mach probe within 6 mm. This compact structure can not only effectively suppress the secondary electron emission effect, but also minimize the disturbance of the detection device to the plasma flow field. The present invention evenly arranges 4 collection electrodes circumferentially around the head of the Mach probe to achieve synchronous measurement of the two-channel orthogonal flow velocity components, which can significantly improve the measurement efficiency of the ion flow velocity. Through a movable vacuum-sealed flange structure, the present invention supports the adjustment of the insertion depth and spatial position of the Mach probe while ensuring the system sealing performance, can diagnose the local flow field structure inside the ion source, reveal the spatial distribution characteristics of the ion flow velocity, has a high spatial resolution, can directly provide the velocity information of particles, and can synthesize three-dimensional data of the ion flow velocity measurement without complex optical path rotation or multiple scans. Moreover, the experimental device is simple and the cost is low. Description of the Drawings

[0018] Figure 1 Fig. is a schematic structural diagram of the Mach probe, in which, 1 - collection electrode, 2 - insulating bracket, 3 - stainless steel protective tube, 4 - movable vacuum-sealed flange, 5 - electrode flange;

[0019] Figure 2 Fig. is a detailed view of the insulating bracket; among them, (a) is a schematic diagram of the upper part of the insulating bracket, and (b) is a schematic diagram of the lower part of the insulating bracket;

[0020] Figure 3 Fig. is a front view and a cross-sectional view of the insulating bracket; among them, (a) is the front view of the insulating bracket, and (b) is the cross-sectional view of the insulating bracket;

[0021] Figure 4 Fig. is a schematic structural diagram of the movable vacuum-sealed flange, in which, 6 - metal pressing plate, 7 - metal pressing ring, 8 - metal cover plate, 9 - KF40 flange;

[0022] Figure 5 Fig. is a circuit structure diagram of the detection system, in which, 1 - collection electrode, 10 - controllable voltage source; 11 - sampling resistor; 12 - voltage acquisition system;

[0023] Figure 6 Fig. is a schematic diagram of the detection process of the Mach probe. Detailed Embodiments

[0024] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] As Figure 1 and Figure 5 shown, the three-dimensional flow velocity distribution detection system of plasma ions of the present invention includes: a Mach probe composed of a collecting electrode 1, an insulating support 2, a stainless steel protective tube 3, a movable vacuum sealing flange 4, and an electrode flange 5, as well as a controllable voltage source 10, a sampling resistor 11, and a voltage acquisition system 12; the Mach probe, the sampling resistor 11, and the controllable voltage source 10 are connected in series through wires to form a loop, and the voltage acquisition system 12 is connected in parallel to the controllable voltage source 10 and the sampling resistor 11 for collecting the voltages of the controllable voltage source 10 and the sampling resistor 11.

[0026] Among them, the material of the collecting electrode 1 is selected as a refractory metal with a relatively high electron work function; preferably, the collecting electrode is four columnar tungsten rods with the same specifications, a diameter of 0.3 mm, and a length of 260 mm, so as to improve the stability and sensitivity of the detection system. As Figure 2 shown, the insulating support 2 is made of high-temperature-resistant alumina ceramic or other high-temperature-resistant ceramic materials, and it consists of two parts with different diameters: the upper part of the insulating support 2 is a cylindrical section with a diameter of 4 mm and a length of 9 mm, and 4 semi-circular top rectangular cross-section (D-shaped) grooves with an axial length of 8 mm are evenly distributed in the circumferential direction, as Figure 2 shown in (a); the lower part of the insulating support 2 is a cylindrical section with a diameter of 5 mm and a length of 250 mm, and 4 through holes (precision installation holes) with the same diameter as the diameter of the collecting electrode 1 are opened inside, forming an axial continuous channel with the 4 D-shaped grooves in the upper part, as Figure 2 shown in (b). The insulating support 2 is used for insulating protection of the four collecting electrodes and ensuring the reliability of electrical connection. The front view and cross-sectional view of the insulating support 2 are as Figure 3 shown, where Figure 3 (a) is the front view of the insulating support, Figure 3 (b) is the cross-sectional view of the insulating support.

[0027] The stainless steel protective tube 3 is 150 mm long, with an outer diameter of 6 mm and an inner diameter of 5.2 mm, and a standard KF16 flange interface is sealed and welded at the bottom.

[0028] Four columnar collecting electrodes 1 are axially inserted into the through holes opened in the cylindrical section of the lower part of the insulating bracket 2. After its top passes through the lower cylinder with a total length of 250 mm, it continues to penetrate into the D-shaped groove structure of the cylindrical section of the upper part of the insulating bracket 2, so that its top just abuts against the top contact plane of the D-shaped groove. Each collecting electrode 1 exposes only half of its side through the D-shaped groove in the upper part of the insulating bracket 2. The bottom of the collecting electrode 1 is connected to the electrode of the electrode flange 5 through a wire. The insulating bracket 2 is inserted into the stainless steel protection tube 3 and fixed to the stainless steel protection tube 3 with ceramic glue; the movable vacuum sealing flange 4 is sleeved on the stainless steel protection tube 3. The electrode flange 5 is sleeved at the end of the stainless steel protection tube 3 and coaxially installed on the stainless steel protection tube 3 with the vacuum sealing flange 4. The interface of the electrode flange 5 is a standard KF16 interface, which is convenient for vacuum sealing with the stainless steel protection tube 3.

[0029] As Figure 4 shown, the movable vacuum sealing flange 4 includes a metal pressing plate 6, a metal pressing ring 7, a metal cover plate 8 and a KF40 flange 9. The metal pressing plate 6, the metal pressing ring 7, the metal cover plate 8 and the KF40 flange 9 are sleeved on the stainless steel protection tube 3 axially from top to bottom in sequence. The upper end face of the metal pressing ring 7 is nested inside the metal pressing plate 6, and an elastic rubber sealing ring is arranged between them. The lower end face of the metal pressing ring 7 and the inner conical surface of the metal cover plate 8 form a self-tightening seal. The metal cover plate 8 is screwed to the inner thread of the metal pressing plate 6 through an external thread, so that the metal pressing ring 7 and the sealing ring generate axial compression deformation to achieve static sealing. A rubber sealing ring is clamped between the lower end face of the metal cover plate 8 and the upper end face of the KF40 flange 9, and they are connected by four groups of circumferentially evenly distributed fastening screws. The Mach probe is sealed with the experimental device to be measured (ion source) through the lower end face of the KF40 flange 9. Finally, the whole probe assembly is vacuum-sealedly connected to the experimental device to be measured (ion source) through the lower ISO-KF40 standard interface of the KF40 flange 9, and the overall structure meets the vacuum sealing requirement of 10 -6 Pa level.

[0030] As Figure 5 shown, taking the setting of two collecting electrodes 1 as an example, the output terminals of the controllable voltage source 10 are respectively connected to each collecting electrode 1 through the sampling resistors 11, and the common terminal is connected to the ion source housing to be grounded. The voltage acquisition system 12 respectively acquires the voltages of the controllable voltage source 10 and each sampling resistor 11. When the Mach probe works in the plasma, the controllable voltage source 10 applies a scanning voltage from negative to positive relative to the plasma to the collecting electrodes 1 of the Mach probe.

[0031] The present invention also provides a method for detecting the three-dimensional flow velocity distribution of plasma ions, including the steps of:

[0032] Step 1, as Figure 6As shown, insert the Mach probe along a certain direction, such as the y-axis direction, into the plasma cavity of the ion source, and adjust the center position of the collection electrode 1 of the Mach probe to the detection point;

[0033] Step 2: Rotate the Mach probe so that the center line connecting the first pair of opposite electrodes is parallel to the x-axis and the center line connecting the second pair of opposite electrodes is parallel to the z-axis;

[0034] Step 3: Connect the output terminals of the controllable voltage source 10 to the 4 collection electrodes 1 of the Mach probe through 4 independent sampling resistors respectively, and connect the common terminal of the controllable voltage source 10 to the ion source housing to form a closed current loop;

[0035] Step 4: Use the voltage acquisition system 12 to synchronously acquire the voltages across the controllable voltage source 10 and the 4 sampling resistors, and take the difference to obtain the voltage values of the 4 collection electrodes 1;

[0036] Step 5: Calculate the current values of each electrode respectively through Ohm's law, and draw the I-V curve of each collection electrode 1 based on the experimental data of the voltage and current of each collection electrode 1;

[0037] Step 6: Extract the saturated ion current and electron temperature from the I-V curves obtained from each collection electrode 1, and calculate the ion flow velocity components in the x-z plane at the detection point respectively by combining the ion flow velocity calculation theory; , ;

[0038] Step 7: Keep the detection point position unchanged, insert the Mach probe along the x-axis direction, and repeat Steps 2-6 to measure the ion flow velocity components in the y-z plane at the detection point; , ; Moreover, keep the detection point position unchanged, insert the Mach probe along the z-axis direction, and repeat Steps 2-6 again to measure the ion flow velocity components in the x-y plane at the detection point; , ;

[0039] Step 8: Adopt the vector synthesis algorithm: , and calculate the flow direction angles , through the direction cosine to obtain the three-dimensional flow velocity of the plasma at the detection point;

[0040] Step 9: Change the spatial coordinates of the detection point at equal intervals, and loop through Steps 1 to 8 for spatial grid scanning measurement to obtain the three-dimensional flow velocity distribution characteristics of the plasma.

[0041] Among them, extracting the saturated ion current and electron temperature includes:

[0042] Step 601: Extract the saturated ion current from the I-V curve. Specifically, extract the current flat-top value corresponding to the negative bias saturation region as the saturated ion current;

[0043] Step 602: Perform a semi-logarithmic transformation on the current values in the transition region of the I-V curve, plot the lnI-V curve, and obtain the fitting straight line through linear regression. Define the reciprocal of the slope of the fitting straight line as the plasma electron temperature of each collection electrode 1;

[0044] Step 603: Take the arithmetic mean of the plasma electron temperatures measured by the 4 collection electrodes 1 as the plasma electron temperature of the current detection point.

[0045] Among them, the steps to obtain the ion flow velocity component in a certain direction include:

[0046] Divide the 4 collection electrodes 1 into two orthogonal groups, and each group consists of a pair of relatively arranged collection electrodes 1. Among them, for each group, one electrode (upstream electrode) faces the positive direction of plasma flow, and the other electrode (downstream electrode) faces the reverse direction of plasma flow. The flow velocity of ions from the upstream electrode to the downstream electrode The calculation formula is:

[0047] ,

[0048] ,

[0049] Among them, is the elementary charge, is the Mach number of ion flow, is the plasma electron temperature of the current detection point obtained in Step 603, is the ion mass, is the calibration factor, is are the saturated ion currents of the upper and lower electrodes respectively.

Claims

1. A plasma ion three-dimensional velocity distribution detection system, characterized in that: include: Mach probe, as well as controllable voltage source, sampling resistor and voltage acquisition system; The Mach probe, the sampling resistor and the controllable voltage source are connected in series through wires to form a loop. The voltage acquisition system is connected in parallel to the controllable voltage source and the sampling resistor to collect the voltage of the controllable voltage source and the sampling resistor. Among them, four collecting electrodes are evenly arranged around the head of the Mach probe.

2. A plasma ion three-dimensional velocity distribution detection system according to claim 1, characterized in that: The Mach probe comprises: 4 columnar collecting electrodes, an insulating bracket, a stainless steel protection tube, a movable vacuum sealing flange, and an electrode flange; Among them, the upper part of the insulating bracket is a cylindrical section with four D-shaped grooves evenly distributed in the circumferential direction; the lower cylindrical section of the insulating bracket has four through holes with the same diameter as the collecting electrode, forming an axial continuous channel with the four D-shaped grooves in the upper part; the four columnar collecting electrodes are axially inserted along the through holes in the cylindrical section of the lower part of the insulating bracket, and then continue to penetrate the D-shaped groove structure of the cylindrical section of the upper part of the insulating bracket 2, so that the top end thereof abuts against the contact plane at the top of the D-shaped groove; the bottom of the collecting electrode is connected to the electrode of the electrode flange through a wire; the insulating bracket is inserted into a stainless steel protective tube and fixed to the stainless steel protective tube; the movable vacuum sealing flange is sleeved on the stainless steel protective tube; the electrode flange is sleeved on the end of the stainless steel protective tube and is vacuum-sealed with the stainless steel protective tube.

3. A plasma ion three-dimensional velocity distribution detection system according to claim 2, characterized in that: The bottom of the stainless steel protection tube is sealed and welded with a standard KF16 flange interface, and the interface of the electrode flange is a standard KF16 interface.

4. A plasma ion three-dimensional velocity distribution detection system according to claim 2, characterized in that: The insulating bracket is fixed to the stainless steel protective tube by ceramic glue.

5. The plasma ion three-dimensional velocity distribution detection system according to claim 2, characterized in that: The collecting electrode is configured as a columnar tungsten rod or a rod of other refractory metal material with a high electron work function.

6. A plasma ion three-dimensional velocity distribution detection system according to claim 2, characterized in that: The movable vacuum sealing flange includes a metal pressure plate, a metal pressure ring, a metal cover plate and a KF40 flange; the metal pressure plate, the metal pressure ring, the metal cover plate and the KF40 flange are sleeved in sequence from top to bottom along the axial direction of the stainless steel protection tube; the upper end face of the metal pressure ring is embedded in the inner side of the metal pressure plate, and an elastic rubber sealing ring is arranged between the two, and the lower end face of the metal pressure ring and the inner conical surface of the metal cover plate form a self-tightening seal; the metal cover plate is screwed with the internal thread of the metal pressure plate through an external thread, so that the metal pressure ring and the sealing ring produce axial compression deformation to achieve static sealing; a rubber sealing ring is clamped between the lower end face of the metal cover plate and the upper end face of the KF40 flange, and are connected by four sets of fastening screws evenly distributed circumferentially; the Mach probe is sealed with the ion source through the lower end face of the KF40 flange.

7. The plasma ion three-dimensional velocity distribution detection system according to claim 2, characterized in that: The insulating bracket is made of high temperature resistant alumina ceramics or other high temperature resistant ceramic materials.

8. A plasma ion three-dimensional velocity distribution detection method, based on the plasma ion three-dimensional velocity distribution detection system according to any one of claims 1 to 7, characterized in that: include: Step 1, inserting the Mach probe into the plasma cavity of the ion source along a certain direction, such as the y-axis direction, and adjusting the center position of the collecting electrode of the Mach probe to the detection point; Step 2, rotating the Mach probe so that the center line of the first pair of relative electrodes is parallel to the x-axis and the center line of the second pair of relative electrodes is parallel to the z-axis; Step 3, connecting the output end of the controllable voltage source to the four collecting electrodes of the Mach probe through four independent sampling resistors, and connecting the common end of the controllable voltage source to the ion source housing to form a closed current loop; Step 4: Use the voltage acquisition system to synchronously acquire the voltage across the controllable voltage source and the four sampling resistors, and obtain the voltage values ​​of the four collecting electrodes by subtracting them; Step 5, calculate the current value of each electrode respectively by Ohm's law, and draw the IV curve of each collecting electrode according to the experimental data of the voltage and current of each collecting electrode; Step 6: Extract the saturated ion current and electron temperature from the IV curve obtained from each collecting electrode, and calculate the ion flow velocity components in the xz plane at the detection point in combination with the ion flow velocity calculation theory. , ; Step 7: Keep the detection point unchanged, insert the Mach probe along the x-axis direction, and repeat steps 2-6 to measure the ion velocity component in the yz plane at the detection point. , ; And, keeping the detection point position unchanged, insert the Mach probe along the z-axis direction, and repeat steps 2-6 again to measure the ion flow velocity component in the xy plane at the detection point , ; Step 8: Use vector synthesis algorithm: , and calculate the flow direction angle using the direction cosines , , the three-dimensional flow velocity of the plasma at the detection point is obtained; Step 9, changing the spatial coordinates of the detection points in an equidistant manner, and cyclically executing steps 1 to 8 to perform spatial grid scanning measurement to obtain the three-dimensional velocity distribution characteristics of the plasma.

9. The method for detecting the three-dimensional flow velocity distribution of plasma ions according to claim 8, characterized in that: In step 6, extracting the saturated ion current and electron temperature includes: Step 601, extracting the saturated ion current from the IV curve, specifically extracting the current plateau value corresponding to the negative bias saturation region as the saturated ion current; Step 602, performing a semi-logarithmic transformation on the current value in the transition region of the IV curve, plotting a lnI-V curve and obtaining a fitting straight line through linear regression, and defining the inverse of the slope of the fitting straight line as the plasma electron temperature of each collecting electrode; Step 603: Take the arithmetic mean of the plasma electron temperatures measured by the four collecting electrodes as the plasma electron temperature of the current detection point.

10. The method for detecting three-dimensional flow velocity distribution of plasma ions according to claim 9, characterized in that: In step 6 and step 7, the step of obtaining the ion flow velocity component in a certain direction includes: The four collecting electrodes are divided into two orthogonal groups, each group consists of a pair of collecting electrodes arranged oppositely; wherein, the upstream electrode of each group faces the positive direction of the plasma flow, and the downstream electrode faces the reverse direction of the plasma flow. The flow speed of ions from the upstream electrode to the downstream electrode is The calculation formula is: ， ， in, is the elementary charge, is the Mach number of the ion flow, is the plasma electron temperature at the current detection point, is the ion mass, is the calibration factor, for are the saturated ion currents of the upper and lower electrodes, respectively.

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