Vacuum Leak Research Articles

Effect of post-sputter polishing on the performance of a disc-shaped Pd/ZrO2/Ni hydrogen membrane

A thin and highly selective Pd/ZrO2/Ni membrane (Pd layer: 3.4–3.7 μm) was fabricated using repetitive cycles of sputtering and polishing processes without any further thermal treatment. Based on the results of a vacuum leak test through the membrane, the polishing step could effectively eliminate some of the defects formed between Pd columns by filling and surface flattening. The prepared Pd membrane exhibited a high hydrogen permeation flux (31.7 ml/min/cm2) and a significantly high H2/N2 selectivity at del-P = 1 bar and 400 °C. The membrane selectivity remained significantly high (24,157 at del-P = 20 bar) even under a large pressure difference.

Development and Analysis of an Electrically Activated Sucker for Handling Workpieces With Rough and Uneven Surfaces

In this study, we designed an electrically activated sucker that can handle workpieces with rough and uneven surfaces. The new sucker uses a motor to drive its blades to form a rotational flow in a shell, generating a cupped negative pressure distribution and a resulting suction force $F$ . Unlike in existing suckers, the rotational flow in the new sucker is formed close to the upper surface of the workpiece and extends to the outermost region of the shell. There is no air inlet or outlet in the space enclosed by the workpiece and the shell and, thus, no inlet or outlet flow is caused. This design solves the traditional problem of vacuum leak, maintains the suction force even for workpieces with rough and uneven surfaces, and works with little energy consumption. Through theoretical analysis and experiments, we studied the key parameters, i.e., the rotational speed ω and inner radius $R_{2}$ of the shell, and clarified the relationships of $F \hbox{-} \omega$ and $F\hbox{-}R_{2}$ . We also investigated the effect of the driving torque, energy consumption, and surface state on the suction force. Furthermore, we used the new sucker to pick up several types of workpieces to confirm its applicability. Finally, we compared the force–energy ratio and force–area ratio of the new sucker with existing suckers and confirmed that the new sucker is superior in terms of force–energy ratio but is inferior in terms of force–area ratio.

Numerical simulation of draining and drying procedure for the ITER Generic Equatorial Port Plug cooling system

For effective vacuum leak testing all cooling circuits serving the ITER vessel and in-vessel components shall be drained and dried so that after this procedure taking less than 100h the purge gas passing through a component has water content less than 100ppm. This process is four-stage, with the first stage using a short blast of compressed nitrogen to blow most of water in the coolant channels out of the circuit. This process is hindered by volumes which trap water due to gravity. To remove the trapped water, it is necessary, first, to heat up the structure by hot and compressed nitrogen, and then water is evaporated by depressurized nitrogen. The cooling system of the ITER Diagnostic Equatorial Port Plugs is of a complicated hydraulic configuration. The system branching might make difficult removal of water from the piping in the scheduled draining mode. The authors have proposed the KORSAR computation code to simulate draining of the GEPP cooling circuit. The numerical simulation performed has made it possible to describe the process dynamics during draining of the entire GEPP cooling circuit and to define the process time, amount and location of residual water and evolution of two-phase flow regime.

On locating a vacuum leak with the indicator fiber particle method

A mathematical model is presented for the interaction of a fiber indicator particle with a free molecular gas flow. An inverse problem for locating a leak is formulated and solved using particular trajectories and kinematic characteristics of the indicator’s motion. Diagnostic signs that are sufficient for locating the leak are revealed.

Vacuum leak search on Wendelstein W7-X using a numerical regression analysis

The stellarator Wendelstein W7-X, a fusion plasma experiment, is almost ready to be set into plasma operation. Seventy superconducting coils produce the magnetic field that is required to confine the plasma. The coils are arranged in a cryostat vacuum vessel in shape of a torus. The superconductors are cooled by supercritical helium down to the nominal operating temperature between 3 K and 4 K. Before operation, vacuum leak search was performed on the machine, both the cryostat and the plasma vessel. Most of the leaks could be fixed; however not all. But the residual helium leak rate is too small to hamper the successful coil operation. A refined leak search is pending for the future, in order to localize and fix all the remaining leaks. This paper describes a numerical regression analysis, performed to localize these remaining leaks. The regression analysis could gain information on the size and position of the leak, and, at least in principle, on the hydraulic helium flow behavior inside the leak channel. It could be a helpful complement to the standard leak search techniques that had been used before.

Beam Tests of Beampipe Coatings for Electron Cloud Mitigation in Fermilab Main Injector

Electron cloud beam instabilities are an important consideration in virtually all high-energy particle accelerators and could pose a formidable challenge to forthcoming high-intensity accelerator upgrades. Dedicated tests have shown beampipe coatings dramatically reduce the density of electron cloud in particle accelerators. In this work, we evaluate the performance of titanium nitride, amorphous carbon, and diamond-like carbon as beampipe coatings for the mitigation of electron cloud in the Fermilab Main Injector. Altogether our tests represent 2700 ampere-hours of proton operation spanning five years. Three electron cloud detectors, retarding field analyzers, are installed in a straight section and allow a direct comparison between the electron flux in the coated and uncoated stainless steel beampipe. We characterize the electron flux as a function of intensity up to a maximum of 50 trillion protons per cycle. Each beampipe material conditions in response to electron bombardment from the electron cloud and we track the changes in these materials as a function of time and the number of absorbed electrons. Contamination from an unexpected vacuum leak revealed a potential vulnerability in the amorphous carbon beampipe coating. We measure the energy spectrum of electrons incident on the stainless steel, titanium nitride and amorphous carbon beampipes. We find the electron cloud signal is highly sensitive to stray magnetic fields and bunch-length over the Main Injector ramp cycle. We conduct a complete survey of the stray magnetic fields at the test station and compare the electron cloud signal to that in a field-free region.

Commissioning of a 60 GHz Gyrotron Superconducting Magnet System on J-TEXT Tokamak

As an attractive auxiliary heating method for J-TEXT, ECRH systems composed of six 200 kW/60 GHz subsystems are under development. The main components of these systems are donated by the Culham Science Center. To rebuild these systems on the site of J-TEXT, a superconducting magnet (SCM) system for the 60 GHz gyrotron has been firstly tested. The SCM consists of two cavity coils, a gun coil and two pairs of trim coils, where the magnetic field is mainly generated by the cavity coils. To confirm the condition of this SCM, firstly vacuum leak detection was done and the resistance variation of the whole coils during cooling was monitored. Then the transverse and axis fields of the SCM were measured with a designed three-dimensional magnetic field measurement device; the measured axis field was compared with the results calculated by the finite element method. Finally, considering the safety of persons and electrical equipments when the SCM is charged, the stray field was detected. The test results indicate that the condition of this SCM is good and can be used for the 60 GHz gyrotron.

The Finite Element Analysis of Vacuum Leak Detection Container

According to the requirement of vacuum leak detection container for small satellite, a set of vacuum leak detection container is developed. This paper discuss the design of model and the finite element analysis of different models. Through calculating the variation of the displacement X, Y, Z and the stress distribution of different parts and the rotation Z of the door flange and casing flange, determining whether the deflection of flange under internal vacuum will cause the sealing ring the fall of the sealing effect.

Vacuum leak search on the Wendelstein 7-X cryostat vessel

A new plasma fusion experiment, the Wendelstein 7-X (W7-X) has been built in the Max-Planck Institute for Plasma Physics in Greifswald, Germany. A cryostat vacuum tank, shaped like a torus, hosts 70 superconducting magnetic coils to produce a toroidal magnetic field that will confine a fusion relevant plasma. The cryostat tank has a volume of about 420 m3 and is equipped with several hundreds of vacuum ports, feed-throughs and service openings. Nested inside the cryostat is the plasma vessel with a volume of about 80 m3, also shaped like a torus. This plasma vessel is connected to the outside by 254 ports that traverse the cryostat. These ports are needed as access for plasma diagnostics, plasma heating and the supply of cooling media. We report in this paper on the vacuum leak search on the W7-X cryostat, both for the internal piping as well as the integral leak search of the entire vessel against air. This is the initial leak search prior to the first cool-down of W7-X. Emphasis is put on the description of the methods, rather than on the results. The technical commissioning of the cryostat vacuum system within a limited time was the primary task; the emphasis was therefore much more on achieving practical results (the leak-tightness) rather than answering fundamental questions.

Experimental study of a remote sealing method for vacuum leak

Vacuum leak is a critical issue for all devices having vacuum system, especially for the large complex experimental facilities. They often have vacuum components integrated which are inaccessible once the assembly was finished. Therefore, if any unacceptable vacuum leaks occur on the cooling/baking channels of the vacuum components, the machine, at least partially, needs to be disassembled before the maintenance, which would cause extensive experimental program downtime and financial costs. An innovative remote sealing method has been studied to permanently repair such vacuum leaks by injecting a sealant called KH-1714 into the channels with pressurized inert gas. Three experiments, that at 10–20 m away sealing different types of leaked components (bellows, circular pipe or rectangle pipe) with leak rates at the level of 10−6–10−5 Pa m3/s, were done to study the feasibility and reliability of the method. The details of the experiments and results were presented and discussed.

Rarefied gas flow in pressure and vacuum measurements

Flows of a gas through the piston-cylinder gap of a gas-operated pressure balance and in a general vacuum system have one aspect in common, namely that the gas is rarefied due, respectively, to the small dimensions and the low pressure. The flows in both systems could be characterised as being in either slip-flow or transition regimes. Therefore, fundamental research of flow in these regimes is useful for both pressure and vacuum metrology, especially for the gas-operated pressure balance where a continuum viscous flow model is widely used for determining the effective area of the pressure balance. The consideration of gas flow using the most suitable assumption would improve the accuracy of such a calculation. Moreover, knowledge about rarefied gas flow will enable gas behaviour in vacuum and low-flow leak detection systems to be predicted. This paper provides useful information about rarefied gas flow in both slip-flow and transition regimes.

Methods of vacuum consolidation and their deformation analyses

Two methods, namely the air-tight sheet method and the vacuum-drain method (sheetless), are generally used to conduct vacuum consolidation in the field. The advantages and disadvantages of both methods and the techniques for preventing vacuum leakage through a middle sand layer in a deposit, as well as the method for maintaining vacuum pressure when large settlement occurs, have been described. Vacuum pressure is an isotropic consolidation pressure applied to a soil deposit, and the deformation induced is different from that induced by a surcharge (e.g. the weight of an embankment). Two typical case histories in Japan are presented and deformation analyses were conducted. In one case history the vacuum-drain method was used with vacuum pressure alone, and in the other a combination of embankment loading and vacuum pressure was applied employing the air-tight sheet method. It is shown that under vacuum pressure loading, the ground deformation (settlement and lateral displacement) can be calculated reliably using a method proposed previously. For the case involving a combination of vacuum pressure and embankment load, the settlements under the embankment centreline can be estimated reasonably assuming one-dimensional deformation conditions.

Characteristics Analysis of Vacuum Gas Leak Detection Signals Based on Acoustic Emission

Gas leaks can cause major accidents resulting in both human injuries and financial losses. Vacuum pressureinduced air leaks lead to the emission of acoustic signals. Vacuum leak tests are implemented in this paper, and signals excited by leaks through apertures of three different diameters are investigated. According to the acoustic emission signal processing theory, several characteristic parameters were utilized to analyze the generation of continuous vacuum leakage acoustic emission signals. Applicable signal characteristics are used to distinguish the vacuumleaks through apertures of different sizes. It can be inferred that the acoustic emission method can detect vacuum gas leaks as they happen, and signal parameter characteristics analysis can be used to distinguish between the different aperture sizes. This paper is of practical significance to the work of acoustic emission vacuum leak detection.

High-power test of a new Bethe-hole directional coupler for the PAL XFEL S-band linac RF system

The directional coupler to be used in the Pohang Accelerator Laboratory X-ray free electron laser (PAL XFEL) under construction since 2011 must satisfy the conditions for operating at a peak power of 400 MW and a repetition rate of 120 Hz. In these operational conditions of the PAL XFEL, the old Bethe-hole directional coupler that was originally designed to be used in the Pohang Light Source linac is more likely to inflict damages on the ceramic window that cause vacuum leaks. Therefore, for the new Bethe-hole directional coupler, the original design has been modified to use a conventional N-type RF vacuum feedthrough for vacuum sealing instead of the ceramic window. The new Bethe-hole directional coupler is designed by using a finite-difference time-domain simulation. We have fabricated a prototype, and the result of a high-power test indicates that the RF performance of the new DC satisfies the specifications of the PAL XFEL S-band Linac RF system.

Recovery from the earthquake and operation of the J-PARC linac

The Japan Proton Accelerator Research Complex (J-PARC) facilities were extensively damaged by the Great East Japan Earthquake on March 2011. At the linac facility, the buildings, especially those above the ground, were severely damaged. Owing to the damage, most of the conventional facilities were unavailable for several months. There were many cracks in the accelerator tunnel, and a large amount of groundwater (approximately 10 tons per day) leaked into the tunnel. The RF cavities and magnets themselves were not seriously damaged; however, vacuum leaks occurred in the ion source, the medium-energy beam transport 1 (MEBT1), and the separated-type drift tube linac (SDTL) sections from the destruction of the vacuum port, beam monitors, and bellows. Therefore, the accelerator components were exposed to highly humid air for several weeks. A maximum misalignment of 0.2 mm of the drift-tube (DT) bore center in the drift tube linac (DTL) was observed. A subsidence of more than 40 mm and a tilt of about 3 mrad were also observed in the accelerator tunnel. After significant recovery efforts, we resumed beam operation in December 2011 and user operation in January 2012. The beam power from the linac reached 13.3 kW in March 2012, which is equal to that just before the earthquake. In this report, we will discuss the recovery from the earthquake and the present operating status of the J-PARC linac.

Predictions of Vacuum Loss of Evacuated Vials from Initial Air Leak Rates

Container closure integrity is a critical factor for maintaining product sterility and stability. Therefore, closure systems (found in vials, syringes, and cartridges) are designed to provide a seal between rubber stoppers and glass containers. To ensure that the contained product has maintained its sterility and stability at the time of deployment, the seal must remain intact within acceptable limits. To this end, a mathematical model has been developed to describe vacuum loss in evacuated drug vials. The model computes equivalent leak diameter corresponding to initial air leak rate as well as vacuum loss as a function of time and vial size. The theory accounts for three flow regimes that may be encountered. Initial leak rates from 10(-8) to 10(3) sccm (standard cubic centimeters per minute) were investigated for vials ranging from 1 to 100 mL. Corresponding leak diameters of 0.25-173 μm were predicted. The time for a vial to lose half of its vacuum, the T50 value, ranged from many years at the lowest leak rates and largest vials, to fractions of a second at the highest leak rates and smallest vials. These results may be used to determine what level of initial vacuum leak is acceptable for a given product.

Spectroscopic Measurement of Neutral Particle Influx Ratio on EAST

The spectra of HeI (587.6 nm), Hα (656.28 nm) and Dα (656.1 nm) of the helium discharges as well as the normal deuterium discharges have been measured with two optical spectroscopic multi-channel analysis (OMA) systems on the experimental advanced superconducting tokamak (EAST). The influx ratio of the sum of H and D to He spectral lines and the influx ratio of H to D are given. In this way the ratio of hydrogen/deuterium ion (S/XB)H/D to (S/XB)He as well as (S/XB)H/D is not very sensitive to the variation in the edge density and temperature. The low-density helium discharges are operated in order to reduce the recycling hydrogen fluxes; however, the effect is not obvious. The possible reason is that the number of helium discharges is not enough and the content of hydrogen in the wall is still very abundant, which is caused by frequent wall conditionings and the vacuum leakage. The H/(H+D) ratio decreases quickly after one lithium coating and reduces to less than 10% using several accumulated lithium wall conditioning. It is found that the deposited He atoms on the carbon wall will remain at a low level after several D2 discharges.

Structural analyses of HV bushing for ITER heating NB system

The HV bushing has a function of a bulk head between insulation gas (SF6) of 0.6MPa and vacuum, which is needed to insulate −1MV in vacuum in ITER heating neutral beam (NB) injection system. Mechanical analyses were carried out to verify the mechanical integrity of the HV bushing composed of five-stage double-layered insulator columns with large brazed ceramic ring and fiber reinforced plastic (FRP) ring of which non-metallic material is required to satisfy a safety factor of ≥3.5. As for the FRP ring required sustaining the pressure load, seismic load and dead weight, it was confirmed that isotropic fiber cloth FRP rings having sufficient strength against shear stress should be used. The shape and fixation area of the Kovar sleeve were modified to lower the stress at the brazing area having vacuum leak tightness and pressure tightness against the air filled at 0.6MPa. As a result, a design of the insulator for the HV bushing was established satisfying the requirement.

火电厂直接空冷技术应用与分析

火力发电厂直接空冷机组作为一种新的节水途径，在我国富煤贫水地区得到广泛推广。本文介绍了直接空冷技术的发展现状、原理及特点、直接空冷技术所凸显的问题，并对直接空冷技术的发展方向做出展望。直接空冷技术常见问题主要包括凝汽器表面积灰、热风再循环、凝汽器防冻度夏、风机运行和真空泄漏。文中阐述了这些问题产生的原因及预防措施，针对问题研究方法做了概括性总结。 Thermal power direct air cooling unit as a new water-saving way, which has been widely promoted in coal-rich and water-poor regions in China. This article describes the direct air cooling technology development status, principles and characteristics, the problems of direct air cooling technology highlights and development direction of direct air cooling technology to make predictions. Common problems of direct air cooling technology include dust accumulation on condenser, hot air recirculation, anti-freezing estivate of condenser, fan running and vacuum leak. This paper describes the causes and preventive measures of these problems and generally summaries the research methods.

PERFORMANCE OF VACUUM CONSOLIDATION IN A THICK CLAYEY DEPOSIT IN SHANGHAI

A vacuum consolidation test was successfully carried out in a (more than 25 m) thick soft clayey deposit in Shanghai. At the site, there is a clayey silt layer located about 5.3 to 6.8 m depth with a relative higher hydraulic conductivity, and a cement deep mixing formed cut-off wall was able to prevent the vacuum leakage through this layer. Prefabricated vertical drains (PVDs) were installed with a spacing of 1.4 m and triangular pattern to a depth of 14 m. The measured results indicate that the degree of vacuum consolidation reached more than 90% in PVD improved zone for a period of about 38 days. Analysis results indicate that the vacuum pressure induced ground deformations can be calculated reasonably well by a previously proposed method. Further field monitoring results show that one month after stopping the vacuum loading, 10 to 65% of the vacuum pressure induced lateral displacement was rebounded, and the percentage rebounding increased with the depth.