An auxiliary vacuum anti-pollution device for a liquid metal target X-ray source vacuum chamber

Abstract

The application relates to an auxiliary vacuum anti-pollution device for a liquid metal target X-ray source vacuum cavity, and belongs to the technical field of liquid metal target X-ray source vacuum maintenance and pre-pump pollution interception. The device comprises a second filter, a vacuum gauge and a vacuum pump arranged in sequence along an auxiliary pumping path, the second filter is located between the vacuum cavity and the vacuum pump, and all the pumped gas passes through the filter medium before reaching the vacuum pump. The second filter adopts multi-stage filter medium with equivalent pore sizes decreasing along the gas flow direction, and can grade and intercept liquid metal droplets, debris and vapor condensates, and the filter core is replaceable; the vacuum gauge represents the vacuum state of the auxiliary pumping path. The device establishes an independent pollution interception pumping path for the jet vacuum cavity without changing the vacuum components of the electron beam system, solves the problems of pumping speed attenuation and pump body pollution caused by the liquid metal entering the vacuum pump, and is used for long-term vacuum maintenance and pre-pump anti-pollution of the liquid metal target X-ray source.

Description

Technical Field

[0001] This invention relates to vacuum maintenance and pre-pump contamination interception technology for liquid metal target X-ray sources, specifically to a contamination prevention device and method that arranges a detachable filter, vacuum gauge, and vacuum pump in the auxiliary pumping path of the jet vacuum chamber. This contamination prevention device operates independently of the vacuum components of the electron beam system itself and is suitable for the graded interception of metal vapor, droplets, and solid debris migrating along the pumping path, vacuum status characterization, and maintainable replacement of the filter media when gallium-based liquid metal jet targets operate for extended periods in high vacuum environments. Background Technology

[0002] The vacuum chamber of a liquid metal jet X-ray source is located at the intersection of electron beam incidence, target vapor generation, and X-ray emission. Metal vapor, droplets, and debris generated when the electron beam bombards the liquid metal can contaminate the vacuum pump, electron gun channel, or vacuum gauge if they migrate along the pumping path.

[0003] Liquid metal jet target X-ray sources use a high-speed circulating gallium-based alloy jet as the anode target. The power deposited by the electron beam at the micron-sized focal spot causes a sharp increase in the local temperature of the target surface. Target material evaporation, jet fragmentation, and collection splashes together constitute a complex source of contamination within the vacuum chamber. Simultaneously, electron gun cathode emission and electron optics focusing require a high vacuum environment on the order of 10^-6 Pa to 10^-7 Pa. The jet vacuum chamber needs to maintain an ultimate vacuum on the order of 10^-5 Pa to 10^-6 Pa under static conditions, and a stable working vacuum on the order of 10^-4 Pa when the jet and electron beam are running simultaneously. Therefore, vacuum maintenance and contamination control become the core contradiction for the long-term reliable operation of this type of X-ray source: the vacuum system must continuously remove contaminant gases while preventing contaminants from entering the pump body and electron beam channel.

[0004] The application of gallium-based liquid metals in vacuum also has its unique characteristics: gallium's saturated vapor pressure is extremely low at room temperature, but the localized high temperature in the scorch bombardment zone increases its evaporation rate by several orders of magnitude; gallium vapor condenses on the pump oil surface, forming a mixed deposit of metal and oil, altering the pump's lubrication and sealing characteristics; gallium has a strong grain boundary embrittlement effect on aluminum alloys, and commonly used aluminum flanges and pipes in vacuum systems may fail if they are in prolonged contact with liquid gallium or its vapor. These characteristics make vacuum contamination prevention for liquid metal target sources different from general dust or water vapor protection, and existing filtration solutions for semiconductor or coating equipment cannot be directly applied.

[0005] Traditional vacuum maintenance solutions often only focus on pumping speed and ultimate vacuum, while liquid metal jet sources also need to consider contaminant interception, filter maintainability, isolation sequence in case of vacuum anomalies, and electron beam channel protection.

[0006] Existing technologies for maintaining vacuum and controlling contamination in jet vacuum chambers have evolved along the following main paths.

[0007] One approach is the direct vacuum pump evacuation scheme: early devices connected the vacuum pump directly to the jet vacuum chamber via a connecting pipe, relying on the pump's nominal pumping speed to maintain the chamber pressure. This scheme is simple in structure, but metal vapor and particles migrating with the evacuation flow continuously deposit in the pump inlet, rotor, or oil circuit. After 100 to 300 hours of operation, a 15% to 30% decrease in pumping speed may occur. When the pump is shut down and the flow reverses, the deposits inside the pump can also contaminate the vacuum chamber, causing the chamber cleanliness to deteriorate cumulatively with the number of operations.

[0008] The second option is the pump inlet filter solution: a standard dust filter or wire mesh is installed at the vacuum pump inlet to intercept particles before the gas enters the pump. However, in the molecular flow and transition flow ranges, the pore structure of the filter material directly determines the flow conductance: reducing the equivalent pore size by one level often reduces the flow conductance by more than half, and the vacuum build-up time is multiplied; increasing the pore size to maintain flow conductance results in a near-complete loss of interception capability for micron- and submicron-sized condensed particles, quickly reducing the filter to a mere formality that only intercepts large particles.

[0009] The third option is a shared electron beam vacuum assembly scheme: to simplify the structure, the jet vacuum chamber is connected to the same high-vacuum pump group where the electron gun is located via a valve, and the vacuum assembly of the electron beam system also handles the evacuation of the jet chamber. This scheme directly directs the high contamination load of the jet chamber to the electron beam channel, which is most sensitive to cleanliness. Metal vapor condenses on the surfaces of the cathode, grid, and high-voltage insulating ceramic parts, causing emission current attenuation, increased high-voltage arcing probability, and degradation of electron optical performance; moreover, any maintenance on the jet side forces the entire gun to break the vacuum, exponentially amplifying the maintenance cost.

[0010] The fourth option is a remote cold trap or baffle solution: a cold trap or baffle is installed in the pipeline far from the vacuum chamber, using low-temperature condensation or inertial retraction to capture condensable components. This solution is far from the contamination source, the long pipeline from the extraction port to the cold trap is contaminated first and difficult to clean online, and local deposits may also detach and fall back into the jet action area; the condensate released during cold trap regeneration requires additional treatment, the maintenance link is long, and it cannot provide close-range protection for the pump.

[0011] When a liquid metal free jet operates in a vacuum environment, it generates a complex contamination load consisting of droplets, splashed debris, surface oxides, and condensable metal vapor. Different contaminants exhibit different migration mechanisms: larger particles are governed by inertia, while condensable vapor migrates along pressure gradients and condenses on cooler surfaces. Simply installing a standard dust filter at the vacuum pump inlet is insufficient to simultaneously address both vacuum conduction and contaminant retention.

[0012] If the vacuum pump is directly connected to the vacuum chamber, steam condensate may form deposits at the pump inlet, causing a decrease in pumping speed or backcontamination after long-term operation. If only a remote filter is used, local deposits may fall back into the jet action zone.

[0013] Vacuum gauges are equally vulnerable in metal vapor environments: the filament of a hot cathode ionization gauge can be corroded by gallium vapor, altering its emission characteristics; electrode sputterings and metal condensation layers of a cold cathode gauge can change its discharge state; and condensation on the hot filament surface of a Pirani gauge can alter its thermal conductivity. If gauge reading drift is not analyzed in conjunction with the pumping process curve, it can easily be misinterpreted as a deterioration of the cavity vacuum. Therefore, the vacuum state characterization methods themselves need to incorporate contamination prevention design.

[0014] The aforementioned evolution scheme has revealed the following technical shortcomings in the engineering application of liquid metal target X-ray sources:

[0015] (1) The contaminants reach the vacuum pump directly along the pumping path, and the pump body becomes the de facto deposition end. Metal vapor condenses at the pump inlet and the surface of the turbine rotor, and particles enter the pump chamber with the airflow. The pumping speed continues to decrease with the running time. More insidiously, the early pump performance decline does not manifest as obvious failure. When the vacuum chamber can no longer establish a working vacuum, the pump body has already been contaminated in a way that is difficult to repair on-site. It can only be returned to the factory for disassembly, cleaning or replacement.

[0016] (2) A single filter screen cannot reconcile the contradiction between retention accuracy and vacuum conductance. The conductance of the flow path within the molecular flow range is strongly correlated with the pore structure. Improving filtration accuracy inevitably sacrifices effective pumping speed and prolongs vacuum build-up time; while the coarse-pore structure that maintains conductance has an extremely low retention rate for submicron condensed particles, allowing particles to still penetrate freely. Existing solutions do not classify the retention structure according to the particle size and morphology of pollutants, causing accuracy and conductance to collide directly on the same layer of filter material.

[0017] (3) The jet vacuum chamber and the electron beam channel share the same vacuum components, causing contamination to spread along the wrong path. The electron gun cathode and high-voltage insulation components are extremely sensitive to metal vapor. Sharing the pumping gas makes the contamination load on the jet side directly threaten the life and stability of the electron beam system. Two vacuum boundaries that should be responsible for different cleanliness levels are mixed together, and fault location and maintenance are mutually constrained. One contamination point will shut down the entire line.

[0018] (4) The vacuum condition characterization method is limited and cannot distinguish the type of fault. When only a single vacuum gauge is installed on the cavity or pump side, the actual air leakage in the vacuum cavity, the gradual blockage of the filter and the decrease in the pumping speed of the vacuum pump are similar in readings. It is difficult for maintenance personnel to determine whether to replace the filter element, check for leaks or repair the pump. Ineffective disassembly and assembly caused by misdiagnosis will introduce new leaks and contamination, forming a vicious cycle of the more it is repaired, the worse it gets.

[0019] (5) The maintenance process itself causes secondary pollution. When the filter element is disassembled under differential pressure, the trapped sediment will be drawn into the vacuum chamber or pump side pipeline by the airflow; when the direction of the contaminated surface of the filter element is unclear and the shell has no supporting structure, the attached layer scraped off during the removal process will also cross the clean boundary. One maintenance will negate the effect of multiple interceptions, which will greatly reduce the actual protective value of the filter device.

[0020] Therefore, the technical challenge that urgently needs to be solved in this field is: how to establish a pre-pump contamination interception link between the contaminant source and the vacuum pump while maintaining the vacuum level maintenance capability of the jet vacuum chamber, which is independent of the vacuum components of the electron beam system and has the functions of particle size classification and interception, diagnosable pumping status and safe replacement of filter media, so that vacuum maintenance is transformed from a simple pumping speed configuration problem into a contaminant migration path control problem. Summary of the Invention

[0021] To address the aforementioned technical deficiencies, the present invention aims to provide an auxiliary vacuum anti-contamination device and method for the vacuum cavity of a liquid metal target X-ray source. This device uses an auxiliary pumping chain, independent of the electron beam system's vacuum components, as its framework. A second filter, which the airflow must pass through, is installed between the jet vacuum cavity and the vacuum pump. Liquid metal droplets, solid debris, and metal vapor condensates migrating with the pumping flow are graded and intercepted at maintainable locations according to particle size and morphology. A comparable cleanliness baseline and operating curve are established using vacuum gauges on the same pumping chain. This ensures that vacuum maintenance, contaminant interception, and fault diagnosis within the vacuum cavity have a clear spatial sequence and a verifiable correspondence, thereby resolving the contradiction between pre-pump contamination interception and secondary contamination maintenance without sacrificing the ability to maintain vacuum levels in a graded manner.

[0022] To solve the above-mentioned technical problems, the present invention adopts the following complementary technical solutions:

[0023] On one hand, an auxiliary vacuum anti-contamination device for a vacuum cavity of a liquid metal target X-ray source is provided, comprising an auxiliary gas extraction passage led out from the vacuum cavity, a second filter disposed on the auxiliary gas extraction passage, a vacuum gauge, and a vacuum pump; the second filter is located between the vacuum cavity and the vacuum pump and has a contaminant receiving side facing the vacuum cavity and a clean side facing the vacuum pump, so that the gas extracted from the vacuum cavity passes through the filter medium before reaching the vacuum pump; the vacuum gauge is used to characterize the pressure state of the auxiliary gas extraction passage; the second filter is configured to trap liquid metal droplets, solid debris, or metal vapor condensate that migrate with the gas extraction flow; along the gas extraction direction of the auxiliary gas extraction passage, the second filter, the vacuum gauge, and the vacuum pump are connected in series, and the second filter constitutes an essential component for all auxiliary gas extraction flows from the vacuum cavity to the vacuum pump.

[0024] Optionally, the second filter includes a filter housing with a vacuum chamber side interface, a vacuum pump side interface and a removable end cap, and a replaceable filter element that is pressed by the end cap and restricts the gas from passing through; a continuous seal is provided between the periphery of the replaceable filter element and the filter housing to prevent airflow from bypassing the periphery of the filter element, and the filter element has a positioning surface in the filter housing that is consistent with the gas extraction direction, and the positioning is restored to be consistent with the original gas extraction direction after reassembly.

[0025] Optionally, the replaceable filter element includes a sintered stainless steel porous body, a metal fiber felt, a ceramic porous body, or a graded filtration structure composed of the like; the graded filtration structure includes at least two layers of filter media arranged sequentially from large to small equivalent pore size along the airflow direction, the upstream layer is used to intercept liquid metal droplets and larger debris, and the downstream layer is used to intercept fine condensed particles, and each layer does not release loose fibers in a vacuum.

[0026] Optionally, the filter housing is provided with a diffusion space and a detachable contaminant receiving part on the vacuum chamber side of the replaceable filter element. The contaminant receiving part is located outside the main air extraction channel. The flow cross-sectional area of ​​the diffusion space is larger than the flow cross-sectional area of ​​the interface on the vacuum chamber side, so that the liquid metal droplets entering with the airflow are decelerated and are received by the contaminant receiving part due to inertial impact. The collection area of ​​the receiving part is set separately from the sealing surface of the housing.

[0027] Optionally, the vacuum chamber side interface of the second filter is connected to the upper part of the vacuum chamber; the vacuum chamber side interface is located above the side of the liquid metal jet action area and is provided with geometric shielding so that the jet body and splashed droplets cannot enter the vacuum chamber side interface in a straight line. The interface diameter is matched with the inlet of the second filter to avoid the interface becoming the main throttling element before the filter element is contaminated.

[0028] Optionally, the auxiliary vacuum anti-contamination device is independent of the vacuum components of the electron beam system itself; the auxiliary vacuum anti-contamination device has an identifiable independent pumping boundary, the contaminant gas flow in the vacuum chamber is not discharged through the vacuum components of the electron beam system itself, and the vacuum components of the electron beam system itself do not replace the vacuum pump to pump the vacuum chamber. The two can serve the jet vacuum chamber and the electron beam channel respectively and are arranged adjacent to each other through a rigid connection interface.

[0029] Optionally, the vacuum gauge is installed between the vacuum pump and the second filter to detect the vacuum status of the auxiliary pumping path. The measuring point of the vacuum gauge can reflect the pressure on the clean side of the second filter, and the measuring range covers 1×10^5 Pa to 5×10^-7 Pa. The change in conductivity of the auxiliary pumping path can be judged by comparing the pumping curve in the clean state with the operating pumping curve. When it is necessary to distinguish the states on both sides of the filter, a cavity pressure measuring point can be added in the vacuum chamber or upstream of the filter to form a pressure difference diagnosis with the pump-side vacuum gauge.

[0030] Optionally, the filter medium of the second filter is made of a material that is resistant to liquid metal corrosion and suitable for vacuum environments; the filter medium is vacuum baked and degassed, and its pore structure does not contain binding components that release volatiles or loose fibers in a vacuum, and enables the vacuum chamber to maintain a working vacuum range of 1×10^-3 Pa to 1×10^-7 Pa.

[0031] Optionally, the second filter is installed in a housing with a vacuum chamber side interface and a vacuum pump side interface with a detachable filter element. The housing is provided with a receiving part on the contaminated side of the filter element to prevent the trapped material from falling into the vacuum chamber or the vacuum pump side pipeline during disassembly. The receiving part is a detachable receiving cup or a drop-proof baffle. When the filter element is disassembled, the receiving part keeps the trapped material on the contaminated side and moves it out together with the filter element.

[0032] The aforementioned technical solution is structured into three mutually supportive layers: the first layer is the spatial sequence layer, establishing an irreplaceable series sequence of vacuum chamber - second filter - vacuum gauge - vacuum pump, structurally closing the contaminant migration path; the second layer is the interception structure layer, using a graded combination of diffusion reception, coarse filtration, and fine filtration to cover three types of loads: droplets, debris, and condensed particles; the third layer is the operational diagnostic layer, using vacuum gauges, clean baselines, and differential pressure criteria to make the interception capability monitorable and recoverable. The combined effect of these three layers distinguishes this device from any partial improvement that merely installs filters, moves pump positions, or adds measuring points.

[0033] On the other hand, a method is provided for maintaining a vacuum in the vacuum cavity of a liquid metal target X-ray source and suppressing contaminant migration using any of the above-described devices, comprising the following steps:

[0034] S1. Start the vacuum pump under the condition that the liquid metal jet and electron beam are turned off, so that the gas in the vacuum chamber flows to the vacuum pump through the second filter, and record the pumping pressure-time curve under clean conditions.

[0035] S2. During the operation of the liquid metal jet, the auxiliary pumping passage is kept open, and the second filter intercepts the liquid metal droplets, solid debris or condensate that migrate with the pumping flow, and the auxiliary pumping status is monitored by a vacuum gauge.

[0036] S3. Compare the air extraction curve after operation with the clean state curve, and distinguish between increased filter resistance, air leakage in the vacuum chamber or changes in vacuum pump performance based on the time to reach the target pressure, stable pressure and measurement effectiveness.

[0037] S4. After confirming that the jet has stopped, the electron beam is disabled, and the pressure difference across the filter has been released, remove the contaminated filter element, keeping the trapped material on the contaminated side and clean the housing.

[0038] S5. After reinstalling the filter element, perform a static seal check and a clean air extraction retest. Only after the air extraction status returns to the allowable range should the liquid metal jet be started.

[0039] Based on the above structural relationships and operational boundaries, the present invention has at least the following beneficial effects:

[0040] (1) The pre-pump interception eliminates the vacuum pump from the role of the end of contamination deposition. The second filter is located at the airflow passage between the vacuum chamber and the vacuum pump. All auxiliary pumping airflow passes through the filter medium before reaching the vacuum pump, and the total interception efficiency for particles of 0.3μm and above can reach more than 99.9%. The pump inlet is kept clean for a long time. The pumping speed reduction caused by contamination is reduced from 15% to 30% (every hundred to three hundred hours) of the direct pumping scheme to a negligible level. The service life of the vacuum pump is no longer determined by contamination, but by its own mechanical life.

[0041] (2) The graded interception based on particle size and morphology resolves the contradiction between interception accuracy and vacuum conductivity. The diffusion space and receiving part first receive high-speed microdroplets in an inertial manner without introducing the resistance of porous media. The upstream coarse layer intercepts larger debris, and the downstream fine layer intercepts condensed particles. Each layer is assigned interception tasks according to the pollution load. The conductivity loss introduced in the clean state can be controlled within 25%, while the equivalent interception accuracy is improved to the submicron level. The graded structure also makes the pollution distribution spread along the airflow direction, and the effective life of the filter element is extended by two to three times compared with a single homogeneous filter material.

[0042] (3) The independent pumping boundary of the electron beam vacuum assembly blocks the erroneous diffusion path of contamination. The high contamination load of the jet vacuum chamber is independently borne by the auxiliary pumping chain. The electron gun cathode, grid and high voltage insulation components no longer face the direct condensation of metal vapor, and the risk of emission attenuation and high voltage arcing is significantly reduced. The two vacuum systems each have identifiable service boundaries. The electron beam channel vacuum is not damaged when maintaining the auxiliary pumping chain. Fault location and maintenance are independent of each other. Maintenance in one place does not require a complete shutdown.

[0043] (4) Vacuum gauges and clean baseline pumping curves enable the diagnosis and differentiation of vacuum anomalies. Based on the clean pressure-time curve, and according to the three characteristics of the time to reach the target pressure, the stable pressure, and the effectiveness of the measurement, three types of faults can be distinguished: increased filter resistance, vacuum chamber leakage, and changes in vacuum pump performance. This avoids confusing vacuum degradation caused by different reasons, reduces new leaks introduced by misdiagnosed disassembly and assembly, and shifts maintenance from experience-based judgment to curve-based criteria.

[0044] (5) The maintenance sequence of receiving part and releasing pressure difference eliminates secondary contamination during the maintenance process. Before disassembly, confirm that the jet has stopped, the electron beam is disabled and the pressure difference on both sides of the filter has been released. The receiving cup or anti-falling baffle keeps the trapped material on the contaminated side and removes it together with the filter element. The trapped liquid metal deposits will not be drawn across the clean boundary by the airflow at the moment of disassembly. A single filter element replacement can be completed in about 30 to 45 minutes without touching the electron beam vacuum assembly. One maintenance does not negate the effect of multiple interceptions.

[0045] (6) The clean baseline after reassembly can be reproduced, supporting the long-term maintenance of vacuum level classification. Static sealing inspection and clean air extraction retest serve as acceptance conditions for resumption of operation, making the deviation of the extraction state from the initial baseline after each filter replacement controllable. The establishment time and stable pressure of the working vacuum of 10^-4 Pa in the jet vacuum chamber remain predictable during long-term operation, and vacuum maintenance is transformed from an empirical operation into a recordable and traceable controlled process.

[0046] The above effects collectively demonstrate that this solution, with pollutant migration path control as its main focus, places the second filter at a necessary point between the vacuum chamber and the vacuum pump, places the vacuum gauge in the same auxiliary pumping chain, and arranges the entire chain independently with the electron beam vacuum assembly. The technical features are interconnected and verifiable by the accompanying drawings and embodiments, rather than being isolated components arranged side by side. Simply placing a filter in the vacuum chamber, monitoring the vacuum separately, or setting up a vacuum pump separately cannot achieve the same pre-pump contamination interception relationship. Attached Figure Description

[0047] Figure 1 The diagram shows the auxiliary pumping chain of the vacuum chamber, second filter, vacuum gauge, and vacuum pump. The diagram marks the vacuum chamber, second filter, vacuum gauge, vacuum pump, and pumping direction. The tandem flow path of the pre-pump filtration and vacuum gauge measurement is shown from the chamber interface to the pump inlet.

[0048] Figure 2 The diagram shows the path of liquid metal contaminants trapped by the second filter. The diagram marks the contaminant-containing airflow, the second filter, liquid metal debris, droplets or condensates, and the filtered airflow. It depicts the migration results of droplet inertial impaction, debris trapping, and condensate retention on the contaminant side.

[0049] Figure 3 The diagram shows a structural comparison of different filter media in the second filter. The diagram marks stainless steel filter element, microporous filter element, ceramic filter element, filter housing, and airflow channel. The pore channels and installation direction of different media are compared under the same housing conditions.

[0050] Figure 4 The diagram shows a cross-sectional view of the connection between the second filter and the upper interface of the vacuum chamber. The upper part of the vacuum chamber, the air extraction port, the second filter, the connecting pipe, and the vacuum gauge are marked in the diagram. The positions of the upper air extraction port, the sealing connection, and the measuring point of the vacuum gauge relative to the direction of the contaminant are shown in the diagram.

[0051] Figure 5 The diagram shows the independent relationship between the auxiliary vacuum device and the electron beam vacuum assembly. The diagram marks the jet vacuum chamber, auxiliary vacuum device, electron beam system, electron beam vacuum assembly, and rigid connection interface, distinguishing the jet chamber auxiliary pumping chain from the electron beam vacuum assembly, and avoiding drawing them as a shared pump circuit.

[0052] Figure 6The diagram shows the status of auxiliary vacuum operation and filter media replacement. The diagram marks the pumping operation status, filter interception status, shutdown status, filter media removal direction, and pumping resumption status. Normal pumping, isolation shutdown, filter element removal, and vacuum reconstruction are distinguished as identifiable statuses. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments of this invention will be further described in detail below with reference to the accompanying drawings. The following discussion unfolds in three levels: analysis of the generation and migration path of contaminants within the jet vacuum chamber, the multi-stage interception mechanism of the second filter and the selection of filter media, and auxiliary vacuum operation conditions and filter media replacement and maintenance. These three levels correspond sequentially to the complete technical logic of where contaminants originate, how they are staged and intercepted, and how the device is operated and maintained long-term. The parameters in the embodiments are determined by material compatibility, design calculations, and prototype testing; unverified fixed values ​​are not considered universally necessary conditions.

[0054] Example 1: Analysis of the generation mechanism and migration path of contaminants in a jet vacuum cavity

[0055] like Figure 1 As shown, in this embodiment, the auxiliary vacuum anti-contamination device consists of a vacuum chamber 101, a second filter 102, a vacuum gauge 103, and a vacuum pump 104 connected in series along the pumping direction 105. The vacuum chamber 101 is the working chamber of the liquid metal jet target. The second filter 102 is connected to the vacuum chamber 101 via a pumping port at the top of the vacuum chamber. The vacuum gauge 103 is located on the pipe section between the second filter 102 and the vacuum pump 104. The vacuum pump 104 is the final power component of the auxiliary pumping chain. All gas flowing out of the vacuum chamber 101 passes through the filter medium of the second filter 102 along the pumping direction 105, and then enters the vacuum pump 104 through the pipe section where the vacuum gauge 103 is located. Following any path from the vacuum chamber 101 to the vacuum pump 104, the gas must first encounter the second filter 102; therefore, the second filter 102 constitutes a necessary component before the contaminated gas flow reaches the vacuum pump 104.

[0056] In this embodiment, the vacuum chamber 101 has a volume ranging from 15 to 35 liters, typically 25 liters. The liquid metal inside the chamber is a gallium-indium-tin eutectic alloy. The jet diameter is 100 μm to 300 μm, the jet velocity is 10 m / s to 30 m / s, and the jet temperature is 40°C to 80°C. The electron beam accelerating voltage is 60 kV to 160 kV, the beam current is 0.5 mA to 5 mA, the focal spot size is 5 μm to 50 μm, and the bombardment power does not exceed 800 W. The vacuum chamber 101 maintains a limiting vacuum on the order of 5 × 10⁻⁶ Pa under static conditions, and stabilizes at a working vacuum of 1 × 10⁻⁴ Pa to 5 × 10⁻⁵ Pa when the jet and electron beam are running simultaneously. The electron gun region is independently maintained by the vacuum components of the electron beam system itself at a higher vacuum on the order of 1 × 10⁻⁶ Pa to 1 × 10⁻⁷ Pa, and the vacuum level classification targets of the two pumping chains are each closed-loop.

[0057] Vacuum level gradation is a prerequisite constraint for the design of this device. The operating range of the auxiliary pumping chain covers the pre-pumping stage starting from atmospheric pressure and the high vacuum stage from 1×10^-3 Pa to 1×10^-7 Pa: in the pre-pumping stage, the forestage dry pump in vacuum pump 104 pumps the vacuum chamber 101 from atmospheric pressure to the 10 Pa level, and then transitions to the 10^-2 Pa level; subsequently, the turbomolecular pump is engaged, bringing the chamber into the high vacuum section. The second filter 102 must maintain its structural integrity and essential relationship with the airflow throughout the entire pressure range: it must not be displaced or bypassed due to the large flow rate impact during the pre-pumping stage, nor should it become the dominant venting source in the high vacuum section, and it must not introduce flow conductance losses exceeding the allowable value in the transition flow region.

[0058] The contaminants within vacuum chamber 101 are categorized into four types based on their generation mechanisms. The first type is bombardment evaporation: the power density at the electron beam focal spot can reach the order of 10^6 W / cm^2, and the instantaneous temperature of the focal spot micro-region is much higher than the temperature of the jet body. Gallium, indium, and tin components evaporate according to their respective saturated vapor pressure differences, forming condensable metal vapors. The second type is jet fragmentation and splashing: the high-speed jet is affected by electron beam impact, surface fluctuations, and collector rebound, generating liquid droplets ranging from 10 μm to 200 μm. The third type is solid debris: the oxide film on the jet surface breaks down, and scale on the collector wall peels off, generating solid particles ranging from 1 μm to 50 μm. The fourth type is condensed particles: metal vapor condenses and nucleates in the chamber's cold walls, near the X-ray window, and within the extraction channel, forming fine condensates ranging from 0.1 μm to 5 μm. The differences in particle size, morphology, and condensability among these four types of contaminants determine that a single filtration mechanism cannot cover the entire load.

[0059] The migration paths of the aforementioned pollutants are different, which is the basis for the arrangement of the interception structure according to the path in this invention. Droplets with a diameter greater than 100 μm mainly settle due to gravity and fall primarily towards the collector area, making it difficult for them to enter the gas extraction port located at the top of the vacuum chamber. Droplets with a diameter of 10 μm to 100 μm are governed by inertia and collide with the wall or receiving surface when the airflow changes direction. Particles and vapor molecules smaller than 10 μm are entrained by the gas extraction flow and migrate towards the gas extraction port along the pressure gradient. Vapor components condense upon encountering low-temperature surfaces during migration, and the condensation location is determined by both the temperature field and pressure field of the chamber. In the molecular flow region, the mean free path of gas molecules is much larger than the characteristic size of the pipe, and pollutants that can be carried by the airflow eventually converge towards the gas extraction port, which becomes the closing point of the pollutant migration path within the vacuum chamber 101.

[0060] The second filter 102 is positioned close to the converging point to intercept the largest possible amount of migrating contaminants with minimal structural cost. Conversely, if the filter element is far from the converging point, the pipe section between the interface and the filter will be contaminated first and difficult to clean online. Local deposits may also detach and fall back into the jet action area, which is precisely the defect exposed by the remote cold trap scheme in the prior art. If the filter element is located after the vacuum pump, the contaminants will have already entered the pump body, rendering filtration meaningless. Therefore, the spatial order of vacuum chamber 101 - evacuation interface - second filter 102 - vacuum gauge 103 - vacuum pump 104 is the irreplaceable functional order of this device.

[0061] From a flow perspective, the auxiliary suction chain spans three regions: viscous flow, transitional flow, and molecular flow. In the initial pre-suction stage, the cavity exhibits viscous flow with a Knudsen number far less than 0.01, resulting in the strongest entrainment capacity of the airflow for particles, making microdroplets most easily carried into the suction channel. As the pressure drops to the 10 Pa to 10^-1 Pa range, it enters the transitional flow, where the entrainment capacity weakens. Upon entering the molecular flow, the mean free path of gas molecules exceeds the characteristic size of the pipe, and particles larger than 10 μm essentially cease migrating with the airflow; the residual load consists mainly of vapor molecules and submicron particles. The second filter 102 faces the greatest flow impact in the viscous flow stage and the finest intercepted objects in the molecular flow stage; its structure and assembly must simultaneously cover both operating conditions.

[0062] Sampling analysis of the aerosol load above the jet action zone shows that, by quantity, 0.1μm to 1μm condensed particles account for approximately 75% to 85% of the particles that can be entrained by the airflow, 1μm to 10μm fine debris accounts for approximately 10% to 20%, and droplets larger than 10μm account for less than 5%; however, by mass, droplets larger than 10μm contribute more than 60%. This inversion of quantity and mass distributions illustrates that selecting filter media solely based on quantity efficiency will underestimate the droplet load, while selecting the receiving structure solely based on mass distribution will underestimate the risk of particle penetration. A staged interception structure must be verified simultaneously based on both distributions.

[0063] The flow rate at the interface during the pre-extraction stage needs to be specifically controlled: when the 25L chamber is evacuated from the atmosphere, the peak volumetric flow rate at the interface can reach tens of liters per second. Direct impact on the filter element can cause droplets to penetrate or the filter element to shift. In this embodiment, a diameter-expanding buffer section is set between the evacuation interface and the second filter 102, which reduces the velocity of the airflow by more than an order of magnitude before it enters the diffusion space; at the same time, the pre-extraction valve adopts a slow-opening control to limit the peak flow rate at the interface to a range that does not stir up the sediment at the bottom of the chamber. This measure, combined with the inertial interception of the receiving part, ensures that the droplet load during the high-flow stage is first received by the resistance-free structure.

[0064] like Figure 4 As shown, the extraction port 402 is located on the side wall of the upper part 401 of the vacuum chamber, above and to the side of the jet action zone, and is equipped with geometric shielding to prevent the jet body and splashed droplets from entering the extraction port 402 in a straight line. The second filter 403 is connected to the extraction port 402 via a connecting pipe 404, and a vacuum gauge 405 is located on the clean side section of the second filter 403. The port diameter matches the connecting pipe 404, which is short and straight, and its inner wall is vacuum cleaned to avoid the formation of a blind cavity for condensate accumulation. This arrangement utilizes the difference between the direction of gravity and the extraction direction to allow large droplets to return to the collection area by gravity, while only allowing fine particles and vapors entrained by the airflow to enter the auxiliary extraction passage, thereby reducing the contamination load of the second filter 403 at the source and slowing down its conductivity attenuation.

[0065] The estimated magnitude of the migration flux further supports the above arrangement. With a jet velocity of 20 m / s and a jet diameter of 200 μm, the flow rate of liquid metal participating in the circulation reaches tens of liters per minute, while the proportion escaping as free droplets is approximately 10^-5 to 10^-4. Of these, only the finest droplets can be carried by the airflow to the extraction port 402. The migration flux of the metal vapor is determined by the bombardment power and the local temperature of the scorch spot. At a bombardment power of 800 W, the vapor condensation load accumulates continuously over operating hours. The dirt-holding capacity of the second filter 102 is designed to match the above flux with the target maintenance cycle: neither too small a margin for frequent replacement nor too large a margin for sacrificing flow conductivity and increasing the cavity outline.

[0066] like Figure 5As shown, the auxiliary vacuum device 502 and the electron beam vacuum assembly 504 of the electron beam system 503 are independent of each other. They are mechanically adjacent only through a rigid connection interface 505, and their pumping lines are not connected. The contaminated gas flow in the jet vacuum chamber 501 is independently discharged by the auxiliary vacuum device 502, while the electron beam vacuum assembly 504 is solely responsible for maintaining the high vacuum of the electron beam channel. This independent arrangement allows for controlled and intercepted contamination loads in the jet vacuum chamber 501, while the electron beam channel remains highly clean. The two do not compromise on the same cleanliness level; any disassembly or maintenance of the auxiliary pumping chain does not disrupt the vacuum of the electron beam channel, and the electron beam vacuum assembly 504 is not forced to undertake pumping loads beyond its design capacity due to contamination loads on the jet side.

[0067] It is important to emphasize that the independence of the auxiliary extraction chain does not preclude coordination at the overall system level: the pump sets of the two extraction chains can share the frame, power supply, and cooling water, and the human-machine interface can be unified for control. However, the extraction pipelines, filtration boundaries, and vacuum measurements are each independent chains, and no shared link constitutes a cross channel for polluted airflow. This definition ensures that independent layout and overall system integration are not contradictory, and also leaves room for flexibility in engineering implementation.

[0068] This embodiment also defines the measurement point logic of vacuum gauge 103. Vacuum gauge 103 is located on the clean side section of the second filter 102, and its reading reflects the pressure state of the filtered passage. During the assembly verification stage, a second measurement point can be temporarily added on the vacuum chamber 101 side. The pressure drop characteristics of the second filter 102 in the transition flow region are calibrated by the difference between the two measurement points. Subsequently, the measurement point can be removed or retained as needed for diagnosis. Regardless of whether a single or dual gauge configuration is used, the clean baseline pumping curve is used as the comparison benchmark for subsequent diagnosis. This avoids directly equating the pump inlet pressure with the vacuum chamber pressure and also avoids using the reading of the electron beam vacuum component, which is unrelated to this auxiliary pumping chain, to replace the state characterization of this chain.

[0069] As can be seen from the analysis of this embodiment, the contamination problem in the vacuum chamber 101 is essentially a migration path problem: as long as the contaminated gas flow inevitably passes through the pumping port to the vacuum pump 104, the path endpoint can be controlled by setting up the necessary second filter 102 between the port and the pump; and the independent arrangement of the electron beam vacuum component ensures that this path does not intersect with the electron beam channel. This path analysis forms the direct basis for the multi-stage interception structure design in Embodiment 2.

[0070] Example 2: Multi-stage retention mechanism of the second filter and verification of filter media selection

[0071] like Figure 2As shown, after the pollutant-containing airflow 201 enters the second filter 202, liquid metal debris 203 and droplets or condensates 204 are trapped on the contaminated side of the filter medium. The filtered airflow 205 continues to flow towards the vacuum gauge and vacuum pump. In this embodiment, the second filter 202 adopts a three-stage interception structure: the first stage is a diffusion space and a detachable receiving part, the second stage is an upstream coarse filter layer, and the third stage is a downstream fine filter layer. The equivalent pore size decreases along the airflow direction in the three-stage structure, so that pollutants of different particle sizes and shapes are trapped at their optimal positions. The interception load is spread along the airflow direction rather than concentrated on a single filter media surface.

[0072] The first stage of interception targets droplets driven primarily by inertia. The filter housing has a diffusion space on the vacuum chamber side of the filter element, with a flow cross-sectional area 2.5 to 4 times that of the exhaust port. As the airflow enters, its velocity decreases, and droplets larger than 10 μm impact the detachable receiving ring or cup located outside the main exhaust channel due to inertia. This stage achieves a rejection efficiency of no less than 95% for droplets larger than 20 μm without introducing any porous media resistance. Its rejection capacity does not decrease over operating time and only requires cleaning during maintenance. The collection area of ​​the receiving part is separated from the housing sealing surface to prevent deposits from entering the clean side along the disassembly joint.

[0073] The second stage of filtration targets solid debris. The upstream coarse filter layer uses metal fiber felt or sintered metal wire mesh with an equivalent pore size of 20μm to 40μm and a porosity of not less than 70%, achieving a filtration efficiency of not less than 99% for solid particles larger than 5μm. This layer also serves as a protection layer for the downstream fine filter layer, preventing larger debris from directly clogging the pores. The third stage of filtration targets condensed particles. The downstream fine filter layer uses sintered stainless steel powder porous material with an equivalent pore size of 3μm to 10μm, achieving a filtration efficiency of not less than 99.9% for particles larger than 0.3μm. After the three stages are combined, the overall filter achieves a total filtration efficiency of not less than 99.97% for particles of 0.3μm and larger, while the conductance loss introduced by the clean state does not exceed 25%. The contradiction between accuracy and conductance is resolved spatially by the graded structure.

[0074] In terms of retention mechanism, microdroplets and larger particles rely on inertial collisions and direct interception to remain on the receiving surface and the surface of the coarse filter layer; submicron particles rely on Brownian diffusion to deposit on the inner wall of the pores of the fine filter layer; when metal vapor passes through the porous medium with the airflow, it condenses into nuclei in the lower-temperature pores, and the condensation nuclei are then retained by the pores. Therefore, the filter medium is not only a geometric screen, but also a condensation bed of steam: its effective retention targets include condensed particles that have just nucleated in the pores. This is precisely the function that ordinary pump inlet filters do not have, and it is also the reason why the second filter must be arranged close to the vacuum chamber to take advantage of the time window when the steam in the chamber has not yet fully condensed.

[0075] like Figure 3As shown, stainless steel filter element 301, microporous filter element 302, and ceramic filter element 303 are compared using the same filter housing 304 and airflow channel 305 to ensure that the selection comparison only reflects the differences in the pore channels and installation direction of the medium itself. The selection of filter media must simultaneously meet four conditions: resistance to gallium-based liquid metal corrosion, low vacuum outgassing, ability to withstand baking and degassing temperatures, and no release of loose fibers. Paper, synthetic fiber, PP, and resin filter elements containing binders continuously release volatiles in high vacuum, becoming additional gas sources, and are not resistant to metal vapor corrosion, and are therefore excluded; aluminum alloy components will become embrittled due to gallium grain boundary penetration and are strictly prohibited from use in housings and filter elements. The selection parameters of the candidate media after vacuum baking and liquid metal compatibility tests are shown in Table 1.

[0076] Table 1. Comparison of Selection Parameters for Candidate Filter Media for the Second Filter

[0077]

[0078] In this embodiment, 316L sintered stainless steel powder porous body is preferred as the fine filter layer, and 316L metal fiber felt is preferred as the coarse filter layer. Neither contains binder, and after vacuum baking at 200℃ for 24 hours, the total outgassing rate meets the requirement of maintaining a static vacuum in the 10^-6 Pa range. The chromium oxide passivation film on the 316L surface provides long-term stability to the gallium indium tin alloy, and the filter element can be repeatedly baked and regenerated. While ceramic porous bodies offer superior temperature resistance and outgassing performance, their thermal shock resistance and edge sealing require verification on a per-unit basis, making them an alternative option for high-temperature applications.

[0079] The following is an example of pumping speed matching calculation. The vacuum chamber volume Vc = 25L, the vacuum pump is a turbomolecular pump with a nominal pumping speed of 300L / s, and a 2L / s backing dry pump; the effective area of ​​the filter element is 260cm², with a clean conductance of approximately 120L / s, the conductance of the connecting pipes and interfaces is approximately 180L / s, and the total conductance of the filter and piping after series connection is approximately 72L / s. The effective pumping speed of the chamber is Se = (1 / 300 + 1 / 72)⁻¹ ≈ 58L / s. The ideal volumetric pumping time t = (Vc / Se)·ln(p0 / p1) is only a few seconds from 10⁻¹Pa to 10⁻⁴Pa. The actual pumping curve is dominated by surface venting and filter material venting. The time for a 25L chamber to reach a clean baseline of 1×10⁻⁴Pa is 25 to 35 minutes. The calculation shows that for every halving of the filter element's conductivity, the effective pumping speed and pumping time of the cavity deteriorate simultaneously. Pumping speed matching must simultaneously calculate both the clean and contaminated endpoint states, and cannot directly replace the effective pumping speed of the cavity with the nominal pumping speed of the vacuum pump.

[0080] The determination of the filtration area follows a dual-state verification: In the clean state, the flow conduction loss introduced by the filter element does not exceed 25%, meaning the effective pumping speed of the cavity after the filter element is installed is not less than 75% of the direct-flow state without a filter element; in the contaminated endpoint state, the flow conduction loss does not exceed 50%, and maintenance is scheduled upon reaching this endpoint rather than continuing operation with defects. Based on the expected contamination load and a maintenance cycle of 800 to 1500 hours, a 260 cm² effective area provides more than twice the contamination capacity for a 25L cavity; for equipment with higher jet power, the filtration area can be increased proportionally to the load, while the airflow sequence and independent arrangement remain unchanged.

[0081] The filter element assembly structure ensures a consistent airflow path. The cylindrical filter element is installed axially along the filter housing, with a removable end cap providing axial restraint. A continuous seal, either a metal sealing ring or a vacuum-tested fluororubber sealing ring, is maintained between the filter element's periphery and the housing, preventing airflow bypass. The clamping force is limited by a locating shoulder to prevent overpressure that could deform the porous structure and reduce porosity. The vacuum sealing of the end cap and the clamping positioning of the filter element are handled by separate structures, avoiding the same weak component bearing both vacuum sealing and filter element positioning simultaneously. After reassembly, the filter element retains its original positioning surface aligned with the original airflow direction.

[0082] The structural details of the filter housing also serve the goal of preventing contamination: the housing is machined as a whole using 304 or 316L stainless steel, and the inner surface is electropolished to reduce vapor condensation and adhesion; the bottom of the diffusion space is inclined towards the receiving cup, so that the condensate film flows into the receiving part and does not accumulate on the end face of the filter element; the vacuum chamber side interface and the pump side interface use knife-edge flanges, so that the pipeline stress is not changed during disassembly and assembly; the housing is equipped with a flow direction nameplate and a contamination side mark, so that maintenance personnel can directly identify the two sides and prevent reverse filling.

[0083] The sealing material around the filter element is selected according to temperature and contamination level: annealed copper metal sealing rings are used for parts baked at temperatures above 200℃ or exposed to high concentrations of metal vapor; vacuum-tested perfluoroether rubber rings can be used for the clean side at room temperature and with low vapor load. The two types of seals have different compression and rebound characteristics. Metal seals rely on the limiting shoulder to control the indentation depth, while rubber seals rely on the compression ratio. When using both, they must be checked separately and cannot be assembled with the same clamping torque.

[0084] The filling sequence for the three-stage structure is as follows: the fine filter layer and the coarse filter layer are filled sequentially from the end cap side, and finally the entire structure is pressed together by the end cap. The receiving cup is then placed in the positioning groove at the bottom of the diffusion space. There is no adhesive between the layers; they are held together by the pressure of the end cap. The filling direction is consistent with the flow direction nameplate on the shell. Reverse filling will cause the coarse filter layer to lose its protective function, and the fine filter layer to be directly subjected to the impact of microdroplets. The maintenance procedure lists checking the filling direction as a mandatory item for reinstallation. The filter element's operating temperature conditions are designed according to the most unfavorable conditions: the filter inlet temperature is 40℃ to 80℃ during continuous jet operation, and the filter element body temperature is 150℃ to 200℃ during baking and degassing. The thermal expansion and contraction caused by temperature cycling is absorbed by the axial floating margin between the filter element and the shell, preventing the porous body from cracking during repeated cycles.

[0085] Sintered stainless steel filter elements support regeneration: After removal, alkaline washing to remove gallium, rinsing with pure water, drying, and vacuum baking, the clean conductivity of the filter element can be restored to more than 90% of that of a new filter element. The number of regeneration cycles is determined by the conductivity recovery rate and the differential pressure baseline, generally not exceeding 5 times. Regeneration of ceramic filter elements requires control of thermal shock; the heating and cooling rate should not exceed 5°C per minute. Regeneration records are included in the maintenance file, and regenerated filter elements are treated as new filter elements to re-establish a clean baseline.

[0086] The scaling rule for filtration area with jet power is as follows: for every doubling of bombardment power, the steam condensation load increases approximately linearly, while the spray droplet load increases even faster. The filtration area scales up to the 1.2 to 1.5 power of the power, with a priority given to increasing the area of ​​the coarse filter layer to protect the fine filter layer. Area scaling is achieved by paralleling filter cartridges or increasing the filter cartridge diameter. The airflow within the housing still converges at the same outlet, without forming external branches that bypass any stage.

[0087] The interception efficiency was verified through an equivalent particle load test. Simulated particles compatible with the liquid metal system were injected upstream of the vacuum chamber at a controlled flow rate. After a specified running time, the filter element's mass before and after the test was weighed, and the pump-side witness plate was inspected. If deposits were concentrated at the receiving section and the upstream surface of the coarse filter layer, no visible particles were found on the clean side of the fine filter layer, and no metal traces were observed on the pump-side witness plate, the interception was deemed effective. If deposits appeared on the clean side, the filter element's through-holes, peripheral bypass, and seal failure were inspected sequentially, rather than directly determining insufficient media precision. Metal vapor condensation load was further assessed based on filter element mass changes and witness plate deposits, avoiding judgment of filter element life solely based on appearance and color.

[0088] The clean-side piping is designed to be short, straight, and with few bends: the length of the pipe section from the second filter outlet to the vacuum gauge does not exceed 300mm; the pipe section from the vacuum gauge to the vacuum pump inlet is directly matched with the pump port flange; there are no more than two bends, and the radius of curvature is not less than 1.5 times the pipe diameter; the inner wall of the pipe is electrolytically polished, and the welds are formed using argon arc welding and helium leak testing, with a leak rate not exceeding 1×10^-9 Pa·m^3 / s. Any deposits in the clean-side piping indicate interception failure; therefore, this section also serves as a visual inspection window for the interception effect, and is checked during maintenance using X-rays or endoscopy.

[0089] The three-stage retention structure and media selection conclusions of this embodiment enable the second filter to simultaneously meet the retention efficiency and conductance requirements across all vacuum level ranges: in the pre-evacuation high-flow stage, the diffusion space and receiving section withstand the microdroplet impact; in the high vacuum stage, the fine filter layer controls particle penetration; and the vapor components are continuously retained on the porous condensation bed. This structure provides the hardware foundation for the operating conditions and maintenance procedures of Embodiment 3.

[0090] Example 3: Auxiliary Vacuum Classification Operation Conditions and Filter Media Replacement and Maintenance Procedures

[0091] like Figure 6 As shown, the operation of the auxiliary vacuum device is divided into five identifiable states: pumping operation state 601, filtration interception state 602, shutdown state 603, filter media removal direction 604, and pumping resumption state 605. This embodiment takes state transition as the main line, defines the operation boundaries and criteria for each state, and makes vacuum maintenance and filter element replacement a repeatable and acceptable controlled process, rather than relying on on-site handling based on the personal experience of maintenance personnel.

[0092] Establish a clean baseline under vacuum operation state 601. After confirming that the liquid metal jet has stopped, the electron beam is disabled, the filter element is installed in the specified direction, and the housing is closed, start the forepump to evacuate the vacuum chamber from atmospheric pressure to the 10 Pa level, and then start the turbomolecular pump. The vacuum gauge continuously records the pressure-time curve, recording the arrival time and stable pressure at each node: 10 Pa, 1 Pa, 10^-1 Pa, 10^-2 Pa, 10^-3 Pa, and 1×10^-4 Pa. For a 25L chamber, the typical characteristics of the clean baseline are: reaching 1×10^-4 Pa takes 25 to 35 minutes, the stable pressure is 3×10^-5 Pa to 8×10^-6 Pa, and the static pressure rise rate after pump shutdown is no greater than 5×10^-4 Pa / h. This curve, along with the chamber temperature and pump status, is archived as the sole benchmark for all subsequent comparisons. After changing the filter batch or maintenance gauge, a new baseline must be established; the old baseline cannot be reused.

[0093] The filter interception status 602 indicates normal service. During jet and electron beam operation, the auxiliary extraction passage remains open, and the second filter continuously traps contaminants migrating with the airflow. The vacuum gauge records the operating pressure at fixed intervals; a slow increase in operating pressure is expected, and instantaneous fluctuations do not directly trigger maintenance. Every 50 hours of operation, the current extraction characteristics are compared with the cleanliness baseline to create a trend record. Maintenance is only scheduled when there is a trend of decreasing conductance, avoiding the use of single-point readings to replace a comprehensive judgment of contamination and extraction capacity.

[0094] Vacuum anomalies are categorized into three types of characteristics. The first type is the time to reach the target pressure: if it takes more than 30% longer than the baseline while the stable pressure is still reached, it indicates decreased flow conductivity, meaning the filter element is clogged or the pipes are deposited. The second type is the stable pressure and static pressure rise: if the stable pressure deteriorates significantly and the pressure rise rate after pump shutdown is more than three times the baseline, it indicates leakage in the vacuum chamber or at the interface; leak detection should be performed, not filter element replacement. The third type is measurement effectiveness: if the vacuum gauge reading drifts or contradicts the pump's operating status, check the gauge tube for contamination and the measurement range first, rather than diagnosing filter failure. These three types of characteristics correspond to different handling paths. The diagnostic conclusions are recorded in four categories: leakage, venting, filter element resistance, and pump performance. Each category corresponds to a different retesting method to avoid ineffective disassembly and reassembly due to general attribution.

[0095] When configuring dual measuring points, the filter cartridge pressure difference in the transition flow zone provides a direct criterion: in the 10^-2 Pa level pumping section, the pressure difference across the clean filter cartridge should not exceed 5% of the upstream pressure; if the pressure difference rises to more than 20% of the upstream pressure, the contamination endpoint is reached, and replacement should be scheduled. When configuring a single measuring point, the equivalent endpoint criterion is that the time to reach 1×10^-4 Pa under the same pump conditions is extended by 50% compared to the baseline. Both criteria must be confirmed through verification tests before implementation: first, isolate the auxiliary pumping chain from the vacuum chamber. If the pump side recovers quickly after isolation but the chamber continues to deteriorate, the main problem lies in the chamber or its interface; if the pump side still cannot recover after isolation, the problem lies in the filter housing, connecting pipe, or pump. Maintenance actions should not be determined based on a single reading.

[0096] The sequence for entering shutdown state 603 is as follows: prohibit high voltage electron beam, stop liquid metal jet and recover liquid metal, wait for the temperature of the jet action zone to drop below 60℃, and release the pressure difference across the filter in the order from the chamber to the pump. Air must not be released by loosening the housing bolts; disassembly before the pressure difference is released will cause trapped deposits to be drawn across the clean boundary by the airflow, which is the main path to secondary contamination and must be eliminated according to procedures.

[0097] The filter element is removed along the filter medium removal direction 604, with the contaminated side facing upward. The receiving cup or fall-preventing retaining edge is moved out together with the filter element, and a sealed tray is used to receive any potentially falling metal particles. The clean side nozzle is immediately capped, and tools for the contaminated side and tools for the clean side are used in separate zones. Record the mass increment and deposition distribution of the removed filter element: deposition concentrated on the receiving part and upstream of the coarse filter layer is a normal interception pattern; deposition that penetrates to the clean side indicates filter element damage or peripheral bypass, and re-installation is allowed only after maintenance. The removed filter medium is disposed of as waste containing liquid metal contaminants, and the housing is cleaned before re-installation with new seals.

[0098] Housing cleaning is carried out from the clean side to the contaminated side, and only attachments on the sealing surface are removed without changing the positioning height. The new filter element to be replaced is pretreated by vacuum baking, with its batch number, equivalent pore size and initial mass recorded. After re-installation, a static seal inspection is performed first: close the pumping path, and a pressure rise of no more than 5×10^-4Pa within 1 hour is qualified. Then proceed to the pumping recovery state 605, measure a new clean pumping curve. The re-installation is determined to be qualified only if the deviation of the time to reach 1×10^-4Pa from the original baseline is within ±15% and the stable pressure is not worse than the baseline. If the stable pressure is qualified but the pumping time increases systematically, check the filter element specification and compression state; if the pumping time is close but the stable pressure deteriorates, prioritize finding re-installation leakage points. These two types of results cannot be replaced by the same ultimate pressure test.

[0099] The maintenance cycle is executed based on the first met of two conditions: cumulative jet operation for 800 to 1500 hours, or the contamination end-point criterion (the pressure difference reaches 20% of the upstream pressure or the pumping time is extended by 50%), whichever comes first. For each maintenance, record the filter element mass increment, deposition area, pump inlet cleanliness and re-measured curve to form a traceable archive; the archive data is also used to verify the filter area margin, and adjust the filter element specification or area when necessary, without changing the mandatory gas flow sequence and independent arrangement relationship.

[0100] The pumping curve patterns of three typical faults have been verified on the prototype: in the controlled micro-leak test, the initial pumping stage is close to the baseline, but the stable pressure rises by more than one order of magnitude and the pressure rise rate after pump shutdown increases by more than three times, and the curve fully recovers after the micro-leak is eliminated; in the stepwise filter element loading test, the arrival time of each pressure node is uniformly extended throughout the whole process, and recovers after replacing with a clean filter element; in the high outgassing surface simulation test, a long tail appears in the medium and low pressure region of the curve and improves gradually with repeated baking. These three patterns are archived as control templates for on-site diagnosis. Maintenance personnel shall classify first and then dispose accordingly, and shall not equate slow filter element contamination with instantaneous chamber leakage.

[0101] The maintenance log must include at least the following fields: maintenance date and cumulative jetting hours, batch of removed filter element and cumulative mass increment, description and image number of the deposition area, pump inlet witness sheet results, new filter element batch and initial mass, static pressure holding results, time of each node on the new clean baseline, retest conclusion and operator. Each maintenance record constitutes one record; baseline differences between adjacent records are used to identify slow drift. If any item fails acceptance, the record must remain open until the retest passes; belt operation cannot be resumed without closing the record.

[0102] Continuous testing data from the prototype showed that, under conditions of 600W jet power and 8 hours of daily operation, the time for the filter element pressure differential to reach the contamination endpoint was 1100 to 1300 operating hours, consistent with the estimated range of 800 to 1500 hours based on flux. After three replacement cycles, no metal deposits were detected on the vacuum pump inlet test strip, and the pump's no-load pumping speed changed by less than 2%. In contrast, the control test, which involved removing the second filter, showed significant deposits at the pump inlet and an 8% decrease in pumping speed after 180 hours. This control directly demonstrates the engineering value of the essential pre-pump interception link.

[0103] In emergency situations such as jet instability or electron beam abnormalities, the safety strategy of the auxiliary evacuation chain is as follows: the electron beam is immediately stopped, the jet drive is reduced in speed according to the program, and the auxiliary vacuum pump continues to evacuate to maintain the negative pressure in the cavity to prevent contaminated gas from escaping through any gaps; the vacuum gauge continuously records the cavity pressure changes during the emergency process as the raw data for accident analysis; only after the cavity pressure returns to below the safety threshold and the filter status is confirmed can the machine be allowed to enter the shutdown state 603 for subsequent inspection.

[0104] Independence verification was performed after each major overhaul: the auxiliary vacuum unit and the electron beam vacuum assembly were isolated separately to confirm that the pumping capacity of the jet vacuum chamber changed only with the status of the auxiliary pumping chain, and the electron beam channel vacuum was unaffected by the disassembly or reassembly of the auxiliary chain; the electron beam vacuum assembly maintained its function during auxiliary chain maintenance, and vice versa. Before the actual beam output, the vacuum status upstream of the filter was linked to the electron gun's permissible conditions: if the pressure exceeded the limit, the electron beam permissible condition was revoked, and the vacuum pump could continue pumping according to the safety strategy. Only when the pressure, rate of change, and measurement validity all recovered were the relevant latches released. This verification and linkage proved that the boundaries of the two pumping chains were always identifiable and independently maintainable.

[0105] The first hour after resuming belt operation is a period of enhanced monitoring: the vacuum gauge records data at a rate of once per minute to confirm that the rate of pressure rise is consistent with the historical curve under the same operating conditions; if the rate of pressure rise is significantly faster than expected in the first hour, it indicates a problem with the new filter element filling direction, the placement of the receiving cup, or the cleanliness of the housing. Immediately return to the shutdown state (603) for re-inspection, and do not allow any accumulated problems to persist. The data from the first hour is incorporated into the maintenance record for this operation as a supplementary reference for the next baseline comparison.

[0106] The acceptance logic of this embodiment corroborates the path analysis in Embodiment 1 and the interception structure in Embodiment 2: the migration path determines the filter location, the interception structure determines the evolution of operating resistance, and the operating procedures ensure that the interception capability is recoverable and reproducible on a scale of hundreds to thousands of hours. Together, these three factors enable the auxiliary vacuum anti-contamination device to maintain the required vacuum level throughout the entire service life of the liquid metal target X-ray source.

[0107] In summary, this invention focuses on controlling the migration path of contaminants within the vacuum chamber. A second filter is positioned at the inevitable airflow path between the vacuum chamber and the vacuum pump. A multi-stage interception structure allocates interception tasks according to particle size and morphology. An auxiliary pumping chain, independent of the electron beam vacuum assembly, blocks the contaminant diffusion path. A clean baseline pumping curve supports fault diagnosis and maintenance acceptance. The above structural relationships and operating procedures have been integrated... Figures 1 to 6 Specific parameters and verification methods are provided, which can be implemented by those skilled in the art; any equivalent adjustments to the filter material specifications, interface forms and criterion thresholds made without departing from the concept of the present invention should be included within the protection scope of the present invention.

Claims

1. An auxiliary vacuum anti-contamination device for the vacuum cavity of a liquid metal target X-ray source, characterized in that, The system includes an auxiliary pumping passage leading from the vacuum chamber, a second filter disposed on the auxiliary pumping passage, a vacuum gauge, and a vacuum pump. The second filter is located between the vacuum chamber and the vacuum pump and has a contaminant-receiving side facing the vacuum chamber and a clean side facing the vacuum pump, allowing the gas extracted from the vacuum chamber to pass through a filter medium before reaching the vacuum pump. The vacuum gauge is used to characterize the pressure state of the auxiliary pumping passage. The second filter is configured to trap liquid metal droplets, solid debris, or metal vapor condensates that migrate with the pumping flow. Along the pumping direction of the auxiliary pumping passage, the second filter, the vacuum gauge, and the vacuum pump are connected in series, and the second filter constitutes an essential component for all auxiliary pumping flows from the vacuum chamber to the vacuum pump.

2. The auxiliary vacuum anti-contamination device according to claim 1, characterized in that, The second filter includes a filter housing with a vacuum chamber-side interface, a vacuum pump-side interface, and a removable end cap, and a replaceable filter element that is pressed and limited by the end cap to allow gas to pass through. A continuous seal is provided between the periphery of the replaceable filter element and the filter housing, preventing airflow from bypassing the periphery of the replaceable filter element, and the replaceable filter element has a positioning surface within the filter housing aligned with the pumping direction.

3. The auxiliary vacuum anti-contamination device according to claim 2, characterized in that, The replaceable filter element includes a sintered stainless steel porous body, metal fiber felt, ceramic porous body, or a graded filtration structure made thereof. The graded filtration structure includes at least two layers of filter media arranged sequentially from large to small equivalent pore size along the airflow direction. The upstream layer is used to trap liquid metal droplets and larger debris, while the downstream layer is used to intercept fine condensed particles.

4. The auxiliary vacuum anti-contamination device according to claim 2, characterized in that, The filter housing has a diffusion space and a detachable contaminant receiving part on the vacuum chamber side of the replaceable filter element. The contaminant receiving part is located outside the main air extraction channel. The flow cross-sectional area of ​​the diffusion space is larger than the flow cross-sectional area of ​​the vacuum chamber side interface, which slows down the liquid metal droplets entering with the airflow and allows them to be caught by the contaminant receiving part due to inertial impact.

5. The auxiliary vacuum anti-contamination device according to claim 1, characterized in that, The vacuum chamber side interface of the second filter is connected to the upper part of the vacuum chamber. The vacuum chamber side interface is located above and to the side of the liquid metal jet action area and is provided with geometric shielding to prevent the jet body and sputtered droplets from entering the vacuum chamber side interface in a straight line.

6. The auxiliary vacuum anti-contamination device according to claim 1, characterized in that, The auxiliary vacuum anti-contamination device is independent of the vacuum components of the electron beam system itself. The auxiliary vacuum anti-contamination device has a identifiable independent evacuation boundary, and the contaminating gas flow in the vacuum chamber is not discharged through the vacuum components of the electron beam system itself, nor does the vacuum components of the electron beam system itself replace the vacuum pump for evacuating the vacuum chamber.

7. The auxiliary vacuum anti-contamination device according to claim 1, characterized in that, The vacuum gauge is installed between the vacuum pump and the second filter to detect the vacuum status of the auxiliary extraction path. The measuring point of the vacuum gauge reflects the pressure on the clean side of the second filter, allowing for the determination of the conductance change in the auxiliary extraction path by comparing the clean state extraction curve with the operational extraction curve.

8. The auxiliary vacuum anti-contamination device according to claim 1, characterized in that, The filter medium of the second filter is made of a material that is resistant to liquid metal corrosion and suitable for vacuum environments. The filter medium is vacuum baked to remove gas, and its pore structure does not contain binding components that release volatiles or loose fibers in a vacuum, and enables the vacuum chamber to maintain a working vacuum range of 1×10^-3 Pa to 1×10^-7 Pa.

9. The auxiliary vacuum anti-contamination device according to claim 1, characterized in that, The second filter is installed in a housing with a vacuum chamber side interface and a vacuum pump side interface, using a removable filter element. The housing has a receiving part on the contaminated side of the filter element to prevent trapped material from falling into the vacuum chamber or vacuum pump side pipeline during disassembly. The receiving part is a removable receiving cup or a drop-proof baffle. When the filter element is disassembled, the receiving part keeps the trapped material on the contaminated side and moves it out together with the filter element.

10. A method for maintaining a vacuum in the vacuum cavity of a liquid metal target X-ray source and suppressing contaminant migration using the apparatus according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Start the vacuum pump under the condition that the liquid metal jet and electron beam are turned off, so that the gas in the vacuum chamber flows to the vacuum pump through the second filter, and record the pumping pressure-time curve under clean conditions. S2. During the operation of the liquid metal jet, the auxiliary pumping passage is kept open, and the second filter intercepts the liquid metal droplets, solid debris or condensate that migrate with the pumping flow, and the auxiliary pumping status is monitored by a vacuum gauge. S3. Compare the air extraction curve after operation with the clean state curve, and distinguish between increased filter resistance, air leakage in the vacuum chamber or changes in vacuum pump performance based on the time to reach the target pressure, stable pressure and measurement effectiveness. S4. After confirming that the jet has stopped, the electron beam is disabled, and the pressure difference across the filter has been released, remove the contaminated filter element, keeping the trapped material on the contaminated side and clean the housing. S5. After reinstalling the filter element, perform a static seal check and a clean air extraction retest. Only after the air extraction status returns to the allowable range should the liquid metal jet be started.

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