A high peak current pulsed glow discharge cleaning method

Abstract

The application discloses a high-peak-current pulse glow discharge cleaning method, and belongs to the technical field of plasma surface treatment. The method comprises the following steps: introducing working gas into a vacuum chamber, so that the gas pressure of the vacuum chamber is maintained within a preset cleaning pressure range; a pulse power source applies a pulse voltage to a glow electrode, so that gas breakdown occurs between the glow electrode and the inner wall of the vacuum chamber, a grounded electrode or a component to be cleaned, and a glow discharge plasma region is formed; the parameters of the pulse power source are adjusted, so that the glow discharge operates in a high-peak-current and low-duty-cycle mode; high-energy particles such as ions in the glow discharge plasma region interact with the inner wall of the vacuum chamber, so that impurities and / or hydrogen isotope fuel adsorbed on the wall surface are released; and the impurity gas and / or hydrogen isotope fuel released from the inner wall surface of the vacuum chamber is discharged. The application can improve the instantaneous discharge intensity during pulse conduction without significantly increasing the average current and average power.

Description

Technical Field

[0001] This invention belongs to the field of plasma surface treatment technology, specifically relating to a high peak current pulse glow discharge cleaning method. Background Technology

[0002] During long-term operation, maintenance, material handling, plasma experiments, or production processes, the inner walls of vacuum chambers easily adsorb water, oxygen, nitrogen, carbon oxides, hydrocarbon molecules, and other residual gaseous impurities. These wall adsorbates and deposits degrade the vacuum recovery rate, the chamber's base vacuum, process stability, and experimental repeatability. For fusion device vacuum chambers, in addition to the aforementioned impurities, hydrogen isotope fuels such as hydrogen, deuterium, and tritium can also accumulate on or near the surface of components such as the first wall, limiter, divertor, and other plasma surfaces. Fuel accumulation not only affects fuel recirculation, plasma breakdown, and stable long-pulse operation, but also involves tritium inventory control, operational safety, and environmental safety for future tritium-containing fusion devices. Therefore, efficient, controllable, and low-risk methods for removing hydrogen isotope fuel accumulation are of great significance.

[0003] Glow discharge cleaning is a commonly used method for cleaning the walls of vacuum chambers. Existing glow discharge cleaning methods mainly employ direct current glow discharge or continuous glow discharge. To improve cleaning efficiency, it is usually necessary to increase the discharge current or the working gas pressure. However, increasing the average discharge current or average power can lead to problems such as increased electrode heat load, temperature rise in the insulation structure, instability in partial discharge, increased risk of arcing, and increased heat load on wall components. Especially in the wall treatment of fusion devices and the removal of hydrogen isotope fuel residues, traditional continuous DC glow discharge is limited by the combined constraints of average current, working gas pressure, arcing risk, and heat load. When further enhancing the cleaning effect is desired, simply increasing the average current will subject the electrodes and wall components to a higher average heat load; simply extending the cleaning time will reduce the device's operating efficiency; and simply increasing the working gas pressure may increase discharge instability and arcing risk. Therefore, existing continuous glow discharge cleaning methods are unable to further improve the instantaneous particle flux and hydrogen isotope release rate under conditions of limited average heat load.

[0004] Therefore, there is an urgent need to propose a high-peak-current pulsed glow discharge cleaning method that can improve instantaneous plasma density, instantaneous particle flux, and wall cleaning efficiency without significantly increasing average current and average heat load, while simultaneously achieving stable arc-free operation. This method can be used for removing impurities from the walls of conventional vacuum chambers as well as for cleaning fuel residues in the vacuum chambers of fusion devices. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] Introduce working gas into the vacuum chamber to maintain the air pressure in the vacuum chamber within the preset cleaning pressure range.

[0007] A pulsed power supply with adjustable pulse frequency, pulse width, average current, and duty cycle is used to apply a pulsed voltage to the glow electrode, causing gas breakdown between the glow electrode and the inner wall of the vacuum chamber, the ground electrode, or the part to be cleaned, and forming a glow discharge plasma region.

[0008] While maintaining the average discharge current or average power within a preset range, one or more parameters of the pulse power supply, such as pulse frequency, pulse width, and duty cycle, are adjusted to enable the glow discharge to operate in a high peak current, low duty cycle mode. The duty cycle D, pulse frequency f, and pulse width τ satisfy D = f × τ × 100%.

[0009] The interaction between high-energy particles such as ions in the glow discharge plasma region and the inner wall of the vacuum chamber releases impurities adsorbed on the wall surface and / or hydrogen isotope fuels that are retained.

[0010] Impurity gases and / or hydrogen isotope fuel released from the inner wall surface of the vacuum chamber are discharged from the vacuum chamber through the vacuum pump assembly pipeline.

[0011] The present invention has the following beneficial effects:

[0012] (1) This invention enables glow discharge to operate with high peak current and low duty cycle by adjusting the pulse frequency, pulse width, and duty cycle. This achieves high peak current while keeping the average current constant or essentially constant, thus decoupling the peak current from the average current. Compared to traditional continuous DC glow discharge, which requires increasing the average current to enhance discharge intensity, this invention can increase the instantaneous discharge intensity during pulse conduction without significantly increasing the average current and average power. This solves the problem of increased average heat load on electrodes, insulation structures, and wall components caused by increased current in continuous DC glow discharge.

[0013] (2) By employing a low duty cycle pulse operation mode, this invention enables the glow discharge to have a high instantaneous current during the pulse conduction period, while allowing for discharge recovery and thermal load buffering time during the pulse interval. Compared to continuous DC glow discharge, which is prone to partial discharge instability and arcing when the working gas pressure or discharge current is increased, this invention can broaden the stable operation window of the glow discharge, reduce the risk of arcing caused by increasing the gas pressure or enhancing the discharge intensity, and facilitate a stable, low-arc-risk or arc-free wall cleaning process.

[0014] (3) The high peak current obtained by this invention can increase the instantaneous discharge intensity, instantaneous plasma density, and instantaneous particle flux during pulse conduction, thereby enhancing the interaction between the plasma and the walls of the vacuum chamber or the surface of the component to be cleaned, and promoting the release of impurities such as water, oxygen, nitrogen, carbon oxides, and hydrocarbon molecules adsorbed on the walls. When this invention is used in the vacuum chamber of a fusion device, it can also enhance the release and removal of hydrogen isotope fuels such as hydrogen, deuterium, and tritium in the first wall, limiter, and divertor.

[0015] (4) Experimental results of this invention show that high peak current pulsed glow discharge can significantly improve hydrogen isotope removal efficiency. In a linear plasma device, using helium as the working gas, with a working pressure of 0.5 Pa and an average current of 1 A, reducing the duty cycle from 100% to 25% increases the peak current from 1 A to 4 A, resulting in an approximately 80% increase in deuterium removal efficiency based on the partial pressure of deuterium. Further increasing the average current while maintaining a duty cycle of 25% increases the peak current from 4 A to 20 A, further improving the deuterium removal efficiency by approximately 193%. These results demonstrate that this invention is not a simple pulsed version of ordinary continuous DC glow discharge, but rather significantly enhances the interaction between plasma and the wall through a high peak current pulsed operation mode, thereby improving hydrogen isotope removal efficiency.

[0016] (5) In the verification of the EAST (Experimental Superconducting Tokamak) device, this invention achieved stable high peak current pulsed glow discharge operation under helium gas conditions of approximately 1 Pa and a single glow electrode; while maintaining an average current of 4 A, the peak current was increased from 8 A to 16 A, and the deuterium removal efficiency was improved by approximately 55%. Therefore, this invention has important application significance for future fusion device wall treatment, hydrogen isotope fuel retention control, tritium safety management, and improvement of plasma start-up conditions. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the implementation of the high peak current pulse glow discharge cleaning method of the present invention, wherein 1-vacuum chamber (chamber to be cleaned), 2-pulse power supply, 3-glow electrode, 4-glow discharge plasma region, 5-working gas charging pipeline, and 6-vacuum pump group pipeline. Detailed Implementation

[0018] 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.

[0019] The purpose of this invention is to provide a high-peak-current pulsed glow discharge cleaning method to solve the problems of high average heat load, limited cleaning efficiency, and insufficient parameter optimization in existing DC glow discharge or continuous glow discharge cleaning processes. This invention includes the following steps:

[0020] S1, introduce working gas into vacuum chamber 1 (the chamber to be cleaned) to maintain the gas pressure in vacuum chamber 1 within a suitable preset cleaning pressure range.

[0021] Specifically, before cleaning, the vacuum chamber 1 is first evacuated through the vacuum pump assembly line 6 to achieve a preset background vacuum condition. Then, working gas is introduced into the vacuum chamber 1 through the working gas filling line 5 to stabilize the pressure within the preset cleaning pressure range. The introduced working gas includes one or more of the following gases: helium, hydrogen, deuterium, argon, neon, oxygen, or nitrogen. Preferably, when the cleaning target is hydrogen isotope fuel retention, helium or a mixture of helium and other gases is used as the working gas to reduce the introduction of additional fuel and enhance fuel release.

[0022] S2, using a pulse power supply 2 with adjustable pulse frequency, pulse width, average current and duty cycle, a pulse voltage is applied to the glow electrode 3, causing gas breakdown between the glow electrode 3 and the inner wall of the vacuum chamber 1, the ground electrode or the part to be cleaned, and forming a glow discharge plasma region 4.

[0023] Specifically, the glow discharge electrode 3 is connected to the positive terminal of the pulse power supply 2, and the inner wall of the vacuum chamber 1, the grounding electrode, or the component to be cleaned serves as the grounding component. After the pulse power supply 2 is activated, a pulsed electric field is established between the glow discharge electrode 3 and the inner wall of the vacuum chamber 1, the grounding electrode, or the component to be cleaned, causing the working gas to break down and forming a glow discharge plasma region 4. The pulse voltage output by the pulse power supply 2 generates a pulsed discharge current in the discharge circuit, and the pulsed discharge current includes a peak current and an average current.

[0024] S3, while maintaining the average discharge current or average power within a preset range, adjust one or more parameters of the pulse frequency, pulse width, and duty cycle of the pulse power supply 2 to make the glow discharge operate in a high peak current and low duty cycle mode; wherein, the peak current of the pulse discharge current is greater than its average current.

[0025] Specifically, the duty cycle D, pulse frequency f, and pulse width τ satisfy D = f × τ × 100%, where D is the duty cycle expressed as a percentage, f is the pulse frequency in Hz, and τ is the pulse width in seconds. By adjusting the pulse frequency and pulse width, the glow discharge operates under low duty cycle conditions. The pulse width of the pulse discharge current is 0.1 μs to 500 μs, preferably 1 μs to 100 μs; the pulse frequency of the pulse discharge current is 0.1 kHz to 500 kHz, and a mutually matched pulse width and pulse frequency are selected according to D = f × τ × 100%, so that the duty cycle D is 1% to 90%, the peak current is 1.5 times to 100 times the average current, preferably 1 kHz to 100 kHz; and the duty cycle of the pulse discharge current is 1% to 90%, preferably 5% to 30%. The average current is the time average of the instantaneous discharge current over one or more complete pulse cycles, and the peak current is the maximum discharge current during pulse conduction. While keeping the average current or average power constant or substantially constant, reducing the duty cycle can increase the peak current during pulse conduction, thereby decoupling the peak current from the average current. The peak current is 1.5 to 100 times the average current, preferably 2 to 50 times.

[0026] S4 utilizes the interaction between high-energy particles such as ions in the glow discharge plasma region 4 and the inner wall of the vacuum chamber 1 to release impurities adsorbed on the wall and / or retained hydrogen isotope fuel.

[0027] Specifically, the impurities include one or more of water, nitrogen, carbon oxides, hydrocarbon molecules, or oxides. When vacuum chamber 1 is a fusion device vacuum chamber or a fusion-related experimental chamber, the hydrogen isotope fuel includes one or more of hydrogen, deuterium, and tritium. The components to be cleaned include one or more of the following: the inner wall of the vacuum chamber, the first wall, the limiter, the divertor, the wall material sample, the sample holder, the diagnostic window, and the inner wall of the port.

[0028] S5, through the vacuum pump assembly pipeline 6, the impurity gas and / or hydrogen isotope fuel released from the inner wall surface of the vacuum chamber 1 are discharged from the vacuum chamber 1.

[0029] Specifically, during the cleaning process, the vacuum pump unit operates continuously, expelling water, nitrogen, carbon oxides, hydrocarbon molecules, adsorbed gases, and hydrogen isotope fuels such as hydrogen, deuterium, and tritium released from the wall surface from the cavity. After cleaning, the pulse power supply 2 and the working gas charging line 5 can be turned off, and vacuum pump unit line 6 can continue to pump air to restore the cavity pressure to the preset range.

[0030] Vacuum chamber 1 can be a low-pressure chamber requiring wall cleaning, including semiconductor process chambers, thin-film process chambers, plasma experimental chambers, fusion device vacuum chambers, or fusion reactor component testing chambers. The above-described chamber types are only used to illustrate the applicable scenarios of this invention and do not constitute a limitation on the scope of protection of this invention.

[0031] When the vacuum chamber 1 is the vacuum chamber of a fusion device, the fusion device includes a magnetic confinement fusion experimental device, which includes a tokamak device, a stellarator device, or other magnetic confinement fusion experimental devices.

[0032] The cleaning method described in this invention can employ either a fixed-parameter cleaning mode or a parameter-optimized cleaning mode. In the fixed-parameter cleaning mode, the pulse frequency, pulse width, duty cycle, peak current, average current, working gas pressure, and working gas type are maintained near preset values ​​to achieve stable cleaning. In the parameter-optimized cleaning mode, the pulse frequency, pulse width, duty cycle, peak current, average current, working gas pressure, or working gas type can be gradually changed, and operating parameters with high cleaning efficiency and stable discharge can be determined based on impurity release, hydrogen isotope fuel release, total pressure changes, or residual gas partial pressure changes.

[0033] During the cleaning process, the discharge voltage, discharge current, voltage change rate, current change rate, average power, or cavity pressure in the output terminal of pulse power supply 2 or the glow electrode 3 circuit can be monitored. When arcing conditions such as a sudden increase in current, a sudden drop in voltage, a voltage and current change rate exceeding preset thresholds (the preset threshold values ​​range from 10A / μs to 100A / μs for current change rate and 10V / μs to 100V / μs for voltage change rate, a current surge multiplier of 1.5 to 5 times, and a voltage drop amplitude of 20% to 50%) or abnormal enhancement of cavity light emission occur, the pulse duty cycle is reduced, the peak current is reduced, the average current is reduced, the pulse output is paused, or the pulse output is turned off to reduce the risk of arcing and maintain stable glow discharge operation.

[0034] The main technical obstacles that this invention needs to overcome include: Traditional continuous DC glow discharge usually relies on increasing the average current or increasing the working gas pressure to improve cleaning efficiency. However, increasing the average current will lead to an increase in the average heat load of electrodes, insulation structures and wall components, while increasing the working gas pressure or increasing the discharge intensity will easily cause partial discharge instability and arcing. At the same time, the instantaneous plasma density and instantaneous particle flux of continuous DC glow discharge are limited by the average current, which leads to a limitation on the release efficiency of wall impurities and hydrogen isotope fuel.

[0035] To address the aforementioned technical obstacles, this invention adjusts the pulse frequency, pulse width, average current, and duty cycle to enable glow discharge to operate with a low duty cycle and high peak current. While maintaining or substantially maintaining the average current or average power, the peak current during pulse conduction is increased by reducing the duty cycle, thereby enhancing the instantaneous discharge intensity without significantly increasing the average heat load. The pulse interval provides time for discharge recovery, space charge dissipation, and heat load buffering, which helps reduce the risk of arcing that easily occurs in continuous DC glow discharge under high pressure or strong discharge conditions. The high peak current also increases the instantaneous plasma density, instantaneous ion flux, instantaneous electron flux, and active particle generation rate during pulse conduction, thereby enhancing the interaction between the plasma and the wall surface and improving the release and removal efficiency of wall impurities and hydrogen isotope fuels.

[0036] In a preferred embodiment, the method of the present invention is used for the removal of hydrogen isotope fuel residue in a fusion device. During cleaning, helium is used as the working gas, and the pressure in the vacuum chamber 1 (fusion device vacuum chamber) is maintained within the range of 0.1 Pa to 10 Pa. The pulse frequency, pulse width, and duty cycle of the pulse power supply 2 are adjusted to ensure stable operation of the glow discharge plasma region 4 under conditions of high peak current and low duty cycle. Ions, electrons, metastable particles, and neutral active particles in the glow discharge plasma region 4 act on the first wall, limiter, or divertor, causing the hydrogen, deuterium, or tritium residue to be released and discharged through the vacuum pump assembly pipeline 6.

[0037] In the deuterium removal experiment verified by the linear plasma device, using helium as the working gas, a working pressure of 0.5 Pa, and an average current of 1 A, reducing the duty cycle from 100% to 25% and increasing the peak current from 1 A to 4 A resulted in an approximately 80% increase in deuterium removal efficiency based on the D2 (deuterium) partial pressure. Further increasing the average current while maintaining a 25% duty cycle increased the peak current from 4 A to 20 A, further improving the deuterium removal efficiency by approximately 193%. These experimental results demonstrate that the present invention does not simply change the power supply method, but rather significantly enhances the plasma-wall interaction through a high peak current and low duty cycle pulsed operation mode, thereby improving the hydrogen isotope fuel removal efficiency.

[0038] In the verification experiment of the EAST superconducting tokamak device, stable high-peak-current pulsed glow discharge operation was achieved using helium as the working gas, at a pressure of approximately 1 Pa, and under single glow electrode conditions. While maintaining an average current of 4 A, the peak current was increased from 8 A to 16 A, resulting in a deuterium removal efficiency improvement of approximately 55%. These results demonstrate that the present invention can achieve stable operation under the complex cavity conditions of a fusion device and can effectively improve the efficiency of hydrogen isotope fuel retention and removal.

[0039] Compared to continuous DC glow discharge, this embodiment enhances the instantaneous discharge intensity by increasing the peak current rather than simply increasing the average current. Therefore, it can improve the efficiency of removing impurities from the wall surface under conditions where the average current or average power is limited. When used in the vacuum chamber of a fusion device, it can also improve the release and removal efficiency of hydrogen isotope fuel residues. The method described in this invention can be implemented based on existing glow discharge cleaning devices. It mainly achieves high peak current pulsed glow discharge cleaning by changing the power supply method, pulse operating parameters, and cleaning control strategy, and has good engineering applicability and promotional value.

[0040] This invention can be used to remove impurities from the walls of conventional vacuum chambers, and is especially suitable for removing hydrogen isotope fuels such as hydrogen, deuterium, and tritium trapped in the vacuum chambers of fusion devices.

[0041] The above description is merely an embodiment of the present invention and does not limit the scope of the invention. Any equivalent structural or procedural transformations made based on the description and drawings of this invention, or direct or indirect applications in other related system fields, are similarly included within the protection scope of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A high-peak-current pulsed glow discharge cleaning method, characterized in that, include: Introduce working gas into the vacuum chamber to maintain the air pressure in the vacuum chamber within the preset cleaning pressure range. A pulsed power supply with adjustable pulse frequency, pulse width, average current, and duty cycle is used to apply a pulsed voltage to the glow electrode, causing gas breakdown between the glow electrode and the inner wall of the vacuum chamber, the ground electrode, or the part to be cleaned, and forming a glow discharge plasma region. While maintaining the average discharge current or average power within a preset range, one or more parameters of the pulse power supply, such as pulse frequency, pulse width, and duty cycle, are adjusted to enable the glow discharge to operate in a high peak current, low duty cycle mode. The duty cycle D, pulse frequency f, and pulse width τ satisfy D = f × τ × 100%. The interaction between high-energy particles such as ions in the glow discharge plasma region and the inner wall of the vacuum chamber releases impurities adsorbed on the wall surface and / or hydrogen isotope fuels that are retained. Impurity gases and / or hydrogen isotope fuel released from the inner wall surface of the vacuum chamber are discharged from the vacuum chamber through the vacuum pump assembly pipeline.

2. The high peak current pulse glow discharge cleaning method according to claim 1, characterized in that, The working gas introduced includes one or more of helium, hydrogen, deuterium, argon, neon, oxygen, or nitrogen.

3. The high peak current pulse glow discharge cleaning method according to claim 1, characterized in that, When the cleaning target is hydrogen isotope fuel residue, helium or a mixture of helium and other gases is used as the working gas.

4. The high peak current pulse glow discharge cleaning method according to claim 1, characterized in that, Before cleaning, the vacuum chamber is first evacuated through the vacuum pump assembly pipeline to achieve the preset background vacuum conditions.

5. The high peak current pulse glow discharge cleaning method according to claim 1, characterized in that, The glow electrode is connected to the positive terminal of the pulse power supply, and the inner wall of the vacuum chamber, the grounding electrode, or the part to be cleaned serves as the grounding component.

6. The high peak current pulse glow discharge cleaning method according to claim 1, characterized in that, The average current is the time average of the instantaneous discharge current over one or more complete pulse cycles, and the peak current is the maximum discharge current during the pulse conduction period, i.e., the peak current is greater than its average current.

7. The high peak current pulse glow discharge cleaning method according to claim 1, characterized in that, Under the condition that the average current or average power remains constant or essentially constant, the peak current during pulse conduction can be increased by adjusting the pulse width and / or pulse frequency and reducing the duty cycle, thereby achieving decoupling between the peak current and the average current.

8. The high peak current pulse glow discharge cleaning method according to claim 1, characterized in that, The pulse width of the pulse discharge current is 0.1μs to 500μs, the pulse frequency is 0.1kHz to 500kHz, and the pulse width and pulse frequency are selected to match each other according to D=f×τ×100%, so that the duty cycle D is 1% to 90% and the peak current is 1.5 times to 100 times the average current.

9. The high peak current pulse glow discharge cleaning method according to claim 1, characterized in that, Impurities include one or more of water, nitrogen, carbon oxides, hydrocarbon molecules, or oxides.

10. The high peak current pulse glow discharge cleaning method according to claim 1, characterized in that, When the vacuum chamber is a fusion device vacuum chamber or a fusion-related experimental chamber, the hydrogen isotope fuel includes one or more of hydrogen, deuterium, and tritium; the components to be cleaned include one or more of the following: the inner wall of the vacuum chamber, the first wall, the limiter, the divertor, the wall material sample, the sample holder, the diagnostic window, and the inner wall of the port.

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