A method for measuring a high-power negative ion source reverse positive ion current

Abstract

The application discloses a method for measuring reverse positive ion current of a high-power negative ion source, and relates to the field of high-current ion source diagnosis.The method comprises the following steps: obtaining the cooling water flow and the temperature of the cooling water on each component of the high-power negative ion source; designing and manufacturing a specific back plate for measuring the profile of the reverse positive ion current; measuring the real-time temperature rise value and the flow of the cooling water on the ion source component, and analyzing the heat deposition on each component; measuring the temperature rise value and the flow of the cooling water on each component under the condition of beam extraction, analyzing the heat deposition on each component, comparing and analyzing the power deposition change on the component bombarded by the reverse positive ion current with and without beam extraction, and obtaining the reverse positive ion current power under the operation parameter; and changing the operation parameter of the negative ion source alone, repeating the experiment, and obtaining the influence law of the parameter on the reverse positive ion current.The application provides a basis for the design and optimization of the back plate of the ion source expansion chamber and the back plate of the Faraday shield and the safe and stable operation of the high-power negative ion source.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of strong current negative ion source, in particular to a method for measuring the reverse positive ion current of a high-power negative ion source, which is used for accurately measuring the energy deposition distribution of the reverse positive ion current generated in the acceleration process of the high-energy negative ion beam, and providing technical support for the heat dissipation design optimization of the ion source and the safe operation of the fusion device. BACKGROUND

[0002] The neutral beam negative ion source includes a plasma generator and an accelerator, and the electrostatic acceleration system adopted accelerates the negative ions (H - / D - ) and the positive ions (H + / D + ) generated due to the collision of high-energy ions with background gas and stripping loss in the acceleration zone and returns them into the expansion chamber and the driver at the same time. The heavy heat burden of the high-energy positive ion flow on the back plate of the expansion chamber and the back plate of the Faraday shield poses a great challenge to the design and processing of the ion source. Meanwhile, the back plate of the expansion chamber and the back plate of the Faraday shield are bombarded by the reverse positive ion flow, which will splash some impurities, affecting the yield of negative hydrogen ions; the high-energy positive ion flow will also enter the expansion chamber, which will affect the yield of negative hydrogen ions by interacting with the electrons, positive and negative ions in the plasma of the expansion chamber, and on the other hand, the high-energy reverse positive ion flow will bombard the back plate of the expansion chamber, causing the cesium deposited thereon to evaporate again and enter the cesium cycle, causing a sudden change in the cesium atomic density, thereby causing a change in the extraction electron / negative ion ratio.

[0003] Therefore, during the extraction process of the long-pulse beam, the reverse positive ion flow has become a problem that cannot be ignored, and a suitable measurement method for the reverse positive ion flow of the strong current negative ion source is urgently needed. The existing measurement system can only obtain the average result of the energy deposition in the ion source components, cannot obtain the spatial distribution of the power density, is difficult to guide the local heat dissipation optimization, and cannot distinguish the energy deposition in different areas, resulting in design redundancy or local overheating risk. Profiling analysis of the reverse ion flow is a necessary condition for heat exchange improvement of the area components bombarded by the reverse ion flow of the high-power negative ion source. SUMMARY

[0004] In order to solve the problem that the traditional measurement system cannot distinguish the power density distribution on a single component, the present application provides a method for measuring the reverse positive ion current of a high-power negative ion source, which supports the profiling measurement of the reverse ion current on the back plate of the expansion chamber and the back plate of the Faraday cylinder, and provides a reliable measurement method for the energy deposition proportion analysis of the reverse positive ion current and the spatial distribution analysis in the components.

[0005] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0006] A method for measuring reverse positive ion current of a high-power negative ion source, comprising:

[0007] An independent cooling inlet and return water path is designed according to measurement requirements;

[0008] The radio frequency power, air pressure, extraction voltage and filtering magnetic field current are fixed, the component energy deposition data of the high-power negative ion source in the beam extraction state are obtained under different acceleration voltages, the component energy deposition data obtained under the condition of no beam extraction are subtracted from the component energy deposition data as reference data, and the energy deposition data caused by the reverse positive ion current is obtained;

[0009] The air pressure, radio frequency power, acceleration voltage and filtering magnetic field current are fixed, the extraction voltage is changed alone, the reference data is subtracted, and the power deposition and power density distribution of the reverse positive ion current on the ion source component are measured;

[0010] The radio frequency power, extraction voltage, acceleration voltage and filtering magnetic field current are fixed, the air pressure is changed alone, the reference data is subtracted, and the power deposition and power density distribution of the reverse positive ion current on the ion source component are measured;

[0011] The air pressure, extraction voltage, acceleration voltage and filtering magnetic field current are fixed, the radio frequency power is changed alone, the reference data is subtracted, and the power deposition and power density distribution of the reverse positive ion current on the ion source component are measured;

[0012] The air pressure, radio frequency power, acceleration voltage and extraction voltage are fixed, the filtering magnetic field current is changed alone, the reference data is subtracted, and the power deposition and power density distribution of the reverse positive ion current on the ion source component are measured;

[0013] The proportion of the power deposition on the ion source component with respect to the change of different operating parameters is obtained, and the local heat exchange is optimized according to the measured deposition power and distribution.

[0014] Advantages:

[0015] 1、The present application realizes the measurement of the power density spatial distribution of the reverse positive ion current of the high-power negative ion source through the division and independent sensor layout of the cooling water path, the measurement unit adopted supports high-precision data acquisition and processing, and is suitable for long-pulse (>1000 s) operation scenarios; since the ion source works in a high-voltage condition, magnets that generate a field are installed in the Faraday cylinder and the back plate of the expansion chamber, on the one hand, there is not enough space to install a thermocouple, on the other hand, the magnetic field will reduce the measurement accuracy of the thermocouple, and the non-contact infrared measurement can avoid such problems.

[0016] 2. This invention designs and installs a one-dimensional CFC (carbon fiber) cylinder for the Faraday shield and expansion chamber backplate, and uses an infrared camera to analyze the energy distribution, thereby achieving cross-sectional analysis of the reverse positive ion flow and measurement of the energy deposition location. This provides a basis for optimizing the heat transfer of the expansion chamber backplate. The data update frequency is ≥50 Hz, meeting the real-time monitoring requirements, and can provide direct support for the heat dissipation design, fault warning, and life assessment of high-power negative ion sources. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the reaction process generated by the reverse positive ion flow in an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of the water flow thermal diagnostic system according to an embodiment of the present invention;

[0019] Figure 3 This is a schematic diagram of carbon materials according to an embodiment of the present invention;

[0020] Figure 4 This is a schematic diagram of the measurement system according to an embodiment of the present invention;

[0021] Figure 5 This is a flowchart of the high-power negative ion source reverse positive ion current measurement method of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention 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 merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0023] like Figure 1 As shown, the radio frequency ion source consists of two parts: a plasma generator and an accelerator. A typical plasma generator structure mainly includes a driver (from outside to inside: coil, ceramic discharge chamber, and Faraday shield) and an expansion chamber. In the accelerator region, in addition to the electrostatic field between the electrodes affecting the trajectory of the reverse positive ions, the distribution of the magnetic field should also be considered. The magnetic field mainly comes from two parts: one is a filtering magnetic field to lower the electron temperature, and the other is a deflection magnetic field embedded in the extraction electrode (EG) to deflect electrons co-extracted with H-.

[0024] The plasma generated by the driver (i.e. Figure 1 The source plasma), after being extracted and accelerated by an accelerator, forms an ion beam (i.e., Figure 1 (The beam of plasma). The accelerator is conducting negative ion (H) - / D -The acceleration also causes positive ions generated by collision of high-energy ions with background gas and stripping loss in the acceleration region to be accelerated and returned into the expansion chamber and the driver (irremovable), and the high-energy positive ion flow brings heavy heat burden to the back plate of the expansion chamber and the back plate of the Faraday shield. The main mechanism of the reverse positive ion generation is electron stripping and ionization produced by collision of negative hydrogen ions with background neutral gas molecules, and the main reaction processes are as follows:

[0025] Stripping process: H - + H2→ H + + 2e + H2;

[0026] H - + H2→ H 0 + e + H2;

[0027] Ionization process: H - + H2→ H2 + + 2e + H 0 ;

[0028] H - + H2→ H + +2e + H2.

[0029] Figure 1 In the formula, PG represents a plasma grid, GG represents a grounded grid, and e represents an electron.

[0030] To solve the above technical problems, as shown in Figure 5 A method for measuring reverse positive ion flow of a high-power negative ion source according to the present application comprises the following steps:

[0031] Step 1: independent waterway design: the cooling waterway of the high-power negative ion source is divided into multiple independent channels (including channels of the expansion chamber sidewall, the expansion chamber back plate, the Faraday shield back plate and the Faraday shield sidewall), and each channel is equipped with an independent flow meter and a high-precision temperature sensor.

[0032] In the step 1, when the flow meter is selected, the following standards are considered: the accuracy is 0.5 level, the working environment temperature that can be supported is-10 ℃-80 ℃, the working pressure range is 0-2.5 MPa, the sampling rate of the flow acquisition module is 2 kHz, the resolution is 12 bit, the sampling rate of the temperature acquisition module is 50-1 kHz, the resolution is 12 bit, the thermocouple type is N type armored shell type, and the accuracy is better than ±0.5 ℃.

[0033] The measurement system is built to synchronously collect the flow rate, the temperature rise of inlet and outlet of each channel by the embedded system; it is assumed that the heat deposited on the component is all taken away by the cooling water, and the energy E deposited on the component (i.e. the component energy deposition data) is calculated by the mass of the cooling water flowing through the component and the temperature curve of the cooling water changing with time as follows:

[0034] (1)

[0035] wherein m is the mass of the cooling water flowing through the component, is the temperature rise of the cooling water flowing through the component, is the specific heat capacity of water, and t is the time variable.

[0036] In the collection time of each shot , formula (1) can be converted to:

[0037] (2)

[0038] In formula (2), the first term can be obtained by numerically integrating the temperature curve obtained by experiment, and the second term is the integral of the cooling water returning to the initial value after the collection time of each shot , which can be determined by data fitting evaluation.

[0039] Most of the components of the neutral beam injection heating system have water cooling channels, and the heat carried by the heat-bearing components of the neutral beam injection heating system can be calculated by the temperature rise of the water flowing through the component, as shown in Figure 2 The water flow heat diagnosis system mainly includes: flow meter, pressure gauge, temperature sensor, flow switch, inlet valve, outlet valve, signal acquisition system and corresponding data processing and analysis equipment (such as computer) and the like. The cooling water in the water cooling channel flows through the temperature sensor to obtain the initial temperature through the inlet valve, and then flows to the heat-bearing components of the neutral beam injection heating system, and in turn passes through the pressure gauge, temperature sensor, flow switch and flow meter, and finally reaches the outlet valve. The data collected by the pressure gauge, temperature sensor, flow switch and flow meter are transmitted to the computer through the signal acquisition system, and the temperature change of the heat-bearing components of the neutral beam injection heating system and the corresponding heat deposition are calculated.

[0040] In order to analyze the profile of the reverse positive ion current, the back plate of the expansion chamber or the back plate of the Faraday shield needs to be specially designed. The specific scheme is as follows: blind holes are opened on the back plate of the expansion chamber or the back plate of the Faraday shield according to a certain distribution, and a cylindrical one-dimensional carbon material is installed in each blind hole. Since the axial thermal conductivity of the one-dimensional carbon material is much greater than the radial thermal conductivity, the temperature at the end of the one-dimensional carbon material can reflect the real-time temperature change of the back plate. In addition, the radial thermal conductivity of the one-dimensional carbon material is small, which can effectively reduce the measurement error caused by radial heat transfer. At the same time, the one-dimensional carbon material has an emissivity close to 1, so the temperature of the one-dimensional carbon material can be clearly obtained in the background by using an infrared imager. By measuring the temperature of the one-dimensional carbon material in the plasma discharge mode and the beam extraction mode, the plasma discharge mode is taken as the background temperature, and the profile distribution of the reverse ion current can be obtained by difference.

[0041] Step 2, obtain the energy deposition values on each component of the high-power negative ion source without beam extraction as reference data, see formula (1), formula (2). Fix the radio frequency power, gas pressure, extraction voltage, set a group of acceleration voltages, and subtract the energy deposition on each component of the high-power negative ion source under different acceleration voltages from the reference data to obtain the energy deposition caused by the reverse positive ion under different acceleration voltages (i.e. Figure 5 the proportion of reverse positive ion energy deposition); combined with the measurement results of the infrared imager (i.e. Figure 5 profile analysis), the energy deposition distribution caused by the reverse positive ion can be obtained.

[0042] Step 3, fix the gas pressure, acceleration voltage, radio frequency power, and filter magnetic field current (i.e. Figure 5 PG current), obtain the energy deposition values on each component of the ion source without beam extraction as reference data. Set a group of ion source extraction voltages, and subtract the energy deposition on each component of the ion source under different extraction voltages from the reference data to obtain the trend of the energy deposition caused by the reverse positive ion with the change of the extraction voltage; combined with the measurement results of the infrared imager (i.e. Figure 5 profile analysis), the energy deposition distribution caused by the reverse positive ion (i.e. Figure 5 the proportion of reverse positive ion energy deposition) can be obtained.

[0043] Step 4, fix the radio frequency power, extraction voltage, acceleration voltage, and filter magnetic field current, set a group of ion source gas pressures, and each time the gas pressure is changed, the measurement results without beam extraction are taken as reference data, and then the measurement results with beam extraction under different gas pressures are subtracted from the reference data to obtain the energy deposition caused by the reverse positive ion under different gas pressures; combined with the measurement results of the infrared imager (i.e. Figure 5 profile analysis), the energy deposition distribution caused by the reverse positive ion (i.e. Figure 5 the proportion of reverse positive ion energy deposition) can be obtained.

[0044] Step 5, fix the gas pressure, the extraction voltage, the acceleration voltage, the filtering magnetic field current, set a group of ion source power, each time the power is changed, the measurement result of the beamless extraction is taken as the reference data, then the measurement results of the beam extraction under different powers are respectively subtracted from the reference data, to obtain the energy deposition caused by the reverse positive plasma under different powers; combined with the measurement results of the infrared imager (i.e. Figure 5 the cross-sectional analysis), the energy deposition distribution caused by the reverse positive plasma (i.e. Figure 5 the proportion of the reverse positive ion energy deposition) can be obtained.

[0045] Step 6, fix the gas pressure, the radio frequency power, the extraction voltage, the acceleration voltage, set a group of ion source filtering magnetic field currents, obtain the energy deposition values on the components of the ion source when the filtering magnetic field current is 0, as the reference data. Subtract the energy deposition on the components of the ion source under different filtering magnetic fields from the reference data, to obtain the energy deposition caused by the reverse positive plasma under different filtering magnetic field currents; combined with the measurement results of the infrared imager (i.e. Figure 5 the cross-sectional analysis), the energy deposition distribution caused by the reverse positive plasma (i.e. Figure 5 the proportion of the reverse positive ion energy deposition) can be obtained.

[0046] Step 7, based on the measurement results, the cooling pipeline design of the high load area is strengthened (i.e. Figure 2 the heat exchange optimization design of the high-power negative ion source).

[0047] Embodiment:

[0048] On the implementation platform of the present application, the filtering magnetic field is generated by two groups of permanent magnets, which are located on both sides of the long side direction of the ion source diagnostic flange and embedded in the bottom of the flange. The distance between the two rows of magnets is 210 mm, and the distance from the plasma electrode is 55 mm. Each magnet has the same three-dimensional size (120 mm x 40 mm x 10 mm), and the material is Sm2Co 17 , the central remanence is set to 1 T at factory. Each group of magnets is installed in a back plate frame made of non-ferromagnetic material for fixation. The magnetic field will affect the trajectory of H + .

[0049] The water flow thermal diagnostic system installed on the implementation platform of the present application is as follows Figure 3As shown, the flow meters are installed in the return water main, in order to observe the flow of each waterway in real time in the control room, all flow meters use instruments with remote data transmission, which can meet the real-time observation in the field and the control room. Considering the complex electromagnetic and 1 MHz RF (radio frequency) interference existing in the working environment of the flow meter, all flow meters select differential pressure flow meters with strong anti-interference ability. The measurement of the temperature rise value of the cooling water adopts the method of installing thermocouples at the water inlet and outlet, and the temperature rise value data of the cooling water are obtained by making a difference. In addition, in order to monitor the pressure condition of the cooling water in the field, pressure gauges are installed on the water inlet and return water main, so as to observe the pressure state of the cooling water in real time in the control room and the field.

[0050] The method for measuring the reverse positive ion current of the high-power negative ion source of the embodiment comprises:

[0051] Step 1: The waterways of the back plate and the side wall of the expansion chamber are separated, and the side wall and the back plate of the Faraday shield are separated by designing the waterways of the expansion chamber and the Faraday shield.

[0052] The cooling water flow rates of the back plate and the side wall of the expansion chamber and the back plate and the side wall of the Faraday shield are measured respectively, and the temperature rise values of the inlet and return water of the four waterways are measured, that is, the energy deposition of the four positions is measured by using the water flow heat method. The upper back plate of the expansion chamber and the upper back plate of the Faraday shield are optimally designed, as shown in Figure 4 As shown in Figure 4 The one-dimensional carbon material is distributed on the upper back plate of the expansion chamber, ​ The circle in

[0053] Step 2: The power of the radio frequency power source is fixed at 50 kW, and the energy deposition of the four positions (the back plate and the side wall of the expansion chamber and the back plate and the side wall of the Faraday shield) is measured in the plasma mode; the reference data is obtained in the plasma mode (without beam extraction), and the energy distribution infrared image of the back plate of the expansion chamber and the upper back plate of the Faraday shield is measured respectively in the beam extraction mode by using the infrared camera. By making a difference with the reference data, the temperature distribution caused by the reverse positive ion current bombardment can be determined, which reflects the profile distribution of the reverse positive ion current; the output power of the RF power source is kept unchanged, the discharge pulse width is kept unchanged, the extraction power (-7 kV) and the acceleration power (-150 kV) are turned on, and the beam extraction time is set to 10 s. Starting from -80 kV, 8 groups of acceleration voltage conditions are measured at a step of 10 kV, and the energy deposition and the temperature distribution in each component under different acceleration voltages are measured. Making a difference with the reference data, the energy deposition and the distribution caused by the reverse positive ion current under different acceleration voltages are obtained.

[0054] Step 3, measure the temperature rise value curve of the cooling water under different extraction voltages, respectively, the numerical integral of the temperature rise value curve is obtained, and the energy deposition is obtained by combining the flow of each cooling water, and the energy distribution is obtained by the infrared camera. The reference data is the same as in step 2, and the energy deposition and its distribution generated by the reverse positive ion flow under different acceleration voltages are obtained by subtracting the data.

[0055] Step 4, under the condition that the extraction voltage, radio frequency power and filtering magnetic field are unchanged, the gas inlet of the high-power negative ion source is adjusted to change the neutral gas molecular density in the electrode acceleration zone, and the influence of the ion source gas inlet quantity on the reverse positive ion flow is evaluated. Under a certain acceleration voltage, the ion source gas inlet quantity is adjusted, the amount of gas inlet quantity is read by the gas mass flowmeter in series in the gas circuit, the discharge gas pressure is adjusted from 0.3 Pa, and the step is 0.1 Pa. The temperature distribution is obtained by analyzing the infrared image.

[0056] Step 5, fix the gas pressure, extraction voltage, acceleration voltage and filtering magnetic field current, set a group of ion source power, and obtain the energy deposition in each part of the high-power negative ion source under different radio frequency powers and temperature distribution changes.

[0057] Step 6, fix the gas pressure, radio frequency power, extraction voltage and acceleration voltage, set a group of ion source filtering magnetic field current, obtain the energy deposition on each part of the ion source when the filtering magnetic field current is 0, as reference data. The energy deposition on each part of the high-power negative ion source under different filtering magnetic field currents is subtracted from the reference data to obtain the energy deposition caused by the reverse positive ion flow under different filtering magnetic field currents; combined with the measurement results of the infrared imager, the energy deposition distribution caused by the reverse positive ion flow can be obtained.

[0058] Step 7, according to the obtained power deposition proportion and energy density distribution results, the cooling pipeline of high-load area, such as the back plate of the expansion chamber, the back plate of the Faraday shield and other components, is optimized and designed. For example, when it is found that the deposited power is too large or the heat distribution is too concentrated, that is, the heat of the component is too high, it means that the heat dissipation needs to be enhanced to dissipate the heat. Therefore, the conventional methods of enhancing heat dissipation can be used as optimization methods, for example, the heat dissipation can be enhanced by increasing the flow of water in the cooling pipeline of the component or increasing the number of cooling pipelines to reduce heat deposition. Or change the material of the cooling pipeline, currently copper material water pipe can be used, can be used to coat molybdenum on the water pipe to enhance heat dissipation and reduce heat deposition.

[0059] While the foregoing specific embodiments of the application have been described in some detail to provide a thorough understanding of the application, it should be apparent that the application is not limited to the specifics of the foregoings as these can, of course, vary. As can be seen, the application can be carried out by specifically constructing devices in accordance with the teaching herein or by practicing acts consistent with the principles of this application. For a better understanding of the application, its operating principles and other objects and advantages, reference should be made to the drawings and to the accompanying descriptive matter.

Claims

1. A method for measuring a reverse positive ion current of a high-power negative ion source, characterized by, The application relates to a method for measuring the power deposition of a high-power negative ion source. According to the measured deposition power and distribution, the local heat exchange is optimized. The deposition power on different components is distinguished according to the temperature rise values of different water channels. The back plate of the extension chamber or the back plate of the Faraday shield of the high-power negative ion source is provided with one-dimensional carbon material, the deposition position of the radio frequency power on the ion source component is reflected, and thus the power density distribution of the reverse positive ion flow is obtained. The component energy deposition data is calculated in each shot collection time according to the mass of the cooling water passing through the component, the temperature rise value of the cooling water passing through the ion source component and the specific heat capacity of the water. The calculation formula of the component energy deposition data E is as follows: When the power deposition and power density distribution of the reverse positive ion flow on the ion source component are measured by fixing the air pressure, the radio frequency power, the acceleration voltage and the filtering magnetic field current and single changing the extraction voltage and subtracting the reference data, only one reference data is collected. When the power deposition and power density distribution of the reverse positive ion flow on the ion source component are measured by fixing the radio frequency power, the extraction voltage, the acceleration voltage and the filtering magnetic field current and single changing the air pressure, the reference data is collected again under the condition of no beam flow every time the air pressure is changed.

2. The method of claim 1, wherein the method is a method of measuring a reverse positive ion current of a high-power negative ion source. When the power deposition and power density distribution of the reverse positive ion flow on the ion source component are measured by fixing the air pressure, the extraction voltage, the acceleration voltage and the filtering magnetic field current and single changing the radio frequency power, the reference data is collected again under the condition of no beam flow every time the radio frequency power is changed.

3. The method of claim 2, wherein the method is a method of measuring a reverse positive ion current of a high-power negative ion source. When the power deposition and power density distribution of the reverse positive ion flow on the ion source component are measured by fixing the air pressure, the extraction voltage, the acceleration voltage and the filtering magnetic field current and single changing the radio frequency power, the reference data is collected again under the condition of no beam flow every time the radio frequency power is changed.

4. The method of claim 2, wherein the method is a method of measuring a reverse positive ion current of a high-power negative ion source. When the power deposition and power density distribution of the reverse positive ion flow on the ion source component are measured by fixing the air pressure, the extraction voltage, the acceleration voltage and the filtering magnetic field current and single changing the radio frequency power, the reference data is collected again under the condition of no beam flow every time the radio frequency power is changed.

5. The method of claim 4, wherein the method is a method of measuring a reverse positive ion current of a high-power negative ion source. The one-dimensional carbon material is in a cylindrical shape. （1） wherein m is the mass of the cooling water passing through the component, is the temperature increase of the cooling water passing through the component, is the specific heat capacity of the water, and t is the time variable. acquisition time of each shot Within each shot's acquisition time, equation (1) becomes: （2） In equation (2), the first term is obtained by numerical integration of the temperature curve from the experiment, and the second term is the acquisition time of each shot After that, the integral of the cooling water returning to the initial value is determined by data fitting evaluation.

6. The method of claim 1, wherein the method is a method of measuring a reverse positive ion current of a high-power negative ion source. ​ 7. The method of claim 4, wherein the method is a method of measuring a reverse positive ion current of a high-power negative ion source. ​ 8. The method of claim 5, wherein the method is a method of measuring a reverse positive ion current of a high-power negative ion source. ​ 9. The method of claim 6, wherein the method is a method of measuring a reverse positive ion current of a high-power negative ion source. ​ 10. The method of claim 3, wherein the method is a method of measuring a reverse positive ion current of a high-power negative ion source. ​

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