Cryopump Research Articles

Design of a 8-kW refrigeration system for ITER common test

Japan Atomic Energy Research Institute is working on the detail design of the helium refrigerator system (8 kW) in order to cool down Central Solenoid Model Coils (CS Model Coils), which will be fabricated and tested in International Thermonuclear Experimental Reactor (ITER) R&D project. The helium refrigerator system consists of supercritical helium cryogenic pump unit, helium refrigerator/liquefier unit, etc. The refrigerator system is designed, considering the various coil operation modes, refrigeration efficiency, economy, and research and development of the cryogenic components required for the ITER.

Thermal design, analysis, and experimental verification for a DIII-D cryogenic pump

As part of the advanced divetoor program, it is planned to install a 50 m 3/s capacity cryopump for particle removal in the DIII-D tokamak. The cryopump will be located in the outer bottom corner of the vacuum vessel. The pump will consist of a surface at liquid helium temperature (helium panel) with a surface area of about 1 m 2, a surface at liquid nitrogen temperature (nitrogen shield) to reduce radiation heat load on the helium panel, and a secondary shield around the nitrogen shield. The cryopump design poses a number of thermal hydraulic problems such as estimation of heat loads on helium and nitrogen panels, stability of the two-phase helium flow, performance of the pump components during high temperature bakeout, and cooldown performance of the helium panel from ambient temperatures. This paper presents the thermal analysis done to resolve these issues. A prototypic experiment performed at General Atomics verified the analysis and increased the confidence in the design. The experimental results are also summarized in this paper.

Design development of a vacuum cryogenic pump with air delivery rates of 20,000 liters/sec

Design development of a vacuum cryogenic pump with air delivery rates of 20,000 liters/sec

極高真空の発生技術について

It passed more than 30 years since the ultra-high vacuum technique was developed. The ultimate pressure available in an ultra-high vacuum system gradually decreased with the advent of sputter ion pumps (SIP), turbomolecular pumps (TMP) and cryopumps (CP), but still remains in the range of 10-9Pa now. Recently there are increasing number of reports for the generation of extremely high vacuum (XHV), which corresponds to the pressure less than 1×10-10Pa. The vacuum pumps used for the generation of XHV are liquid-nitrogen cooled sublimation pumps, liquid-helium and liquid-nitrogen cooled cryopumps, and helium-refrigerator cooled cryopumps. They are closely related with cryogenic engineering. We summarize recent successful works for the generation of XHV. The production technique of XHV is advancing steadily, but total and partial pressure gauges which can measure such low pressure without disturbing vacuum condition have not been developed yet, and they are strongly demanded.

Preparation of NdBa2Cu3O7−δ films in ultrahigh vacuum with a NO2 supersonic molecular beam

Superconducting NdBa2Cu3O7−δ thin films have been prepared in ultrahigh vacuum by the molecular beam epitaxy (MBE) method using a supersonic molecular beam of nitrogen dioxide as an oxidizing agent. A new type of supersonic molecular beam source has been developed, which has a liquid nitrogen trap for cryogenic pumping and is small enough in size to be installed in a conventional MBE system. Films with a transition temperature of about 30 K have been obtained in situ without post-deposition annealing. Throughout deposition epitaxial growth of the films was observed in situ by reflection high-energy electron diffraction.

Comparison of Low-and High-Voltage SEM Images of Beryllium

Beryllium has a low secondary electron (SE) coefficient that produces a low signal-to-noise ratio, and in the past, this deficiency caused many workers to routinely coat beryllium with a high-Z material such as Au/Pd and examine the specimens at high voltage (HV). In principle, beryllium should be an ideal candidate for improved imaging with low voltage (LV), because its low atomic number permits excessive electron-beam penetration during HVSEM imaging — the use of LVSEM to analyze beryllium films was demonstrated previously. Unfortunately, low SE emission can seriously compromise LVSEM images from uncoated beryllium specimens, even with the improved LVSEM imaging capability of a SEM equipped with a field-emission gun (FESEM). This work demonstrates that some beryllium structures yield improved results with LVSEM imaging in a FESEM, particularly at low magnifications, while structures that require high magnification often yield better results with HVSEM.Specimens selected for this study include craters formed by a Cs+ ion beam in specimens that had been analyzed in an ion microanalyzer by secondary-ion mass spectroscopy (SIMS), machined surfaces, and fracture surfaces. SE images were obtained for this study with a Hitachi S-800 FESEM equipped with a cryogenic vacuum pumping system.Surface structure in a sputtered SIMS crater is shown at 2.0 kV in Fig. 1a and at 20 kV in Fig. 1b. This specimen was from commercial grade beryllium sheet. Prominent microtwins are visible in several grains in Fig. 1, and because of the excessive beam penetration at HV, the microtwins are better defined at LV in Fig. 1a than they are at HV in Fig. 1b. In addition, a fine faceted microstructure was formed by the ion beam that could be observed at intermediate magnifications, and it also was better defined at LV than at HV. The dark contamination film that is visible around some of the particles in Fig. 1a also is significant; this film was not apparent at voltages of 5 kV and higher, as demonstrated in Fig. 1b. SIMS ion images revealed that this material contained particles of several different compositions including carbides; since beryllium carbide hydrolyzes when exposed to moist air, the films are suspected to have formed by the decomposition of carbides when the specimen was removed from the ion microanalyzer after the SIMS analysis. This example demonstrates the excellent sensitivity of LVSEM to detect thin films, and it also suggests that contamination and the thin oxide film that forms on beryllium may impair SE imaging.

Operation of cryogenic vacuum pumps in severe environments

Because of their high speed, clean vacuum environment, and life cycle cost advantages, cryogenic vacuum pumps have become the pump of choice in many vacuum processes. Since they are concentrating agents rather than throughput pumps, they can pose a potential hazard in some environments. The potentially dangerous environments fall into three categories: first, where severely reactive agents are used as process gases and are cryopumped in significant quantities, second, where hydrogen is used and pumped in large quantities; and third, where hazardous and unsuspected agents are produced by the process itself. Each class of severe environment is discussed and evaluated from a system safety viewpoint.

The cryogenic diffusion pump and its implementation in a complete fusion reactor forevacuum system

A cryogenic diffusion pump has been developed and tested. It uses the main constituent of the fusion reactor exhaust gas, i.e., deuterium–tritium (D–T), as a working fluid in a diffusion pump operating at low temperature, to separate and compress the minor constituent 4He. Since a suitable tritium-handling facility was not available, a prototype was tested using mixtures of deuterium with 1%, 2%, and 4% helium. As the deuterium is pumped by cryocondensation at 4 K, the entrained helium is staying in the gas phase, is compressed, and leaves the pump outlet at pressures up to 80% of the total inlet pressure. Compression ratios of up to 80 (for 1% helium) and inlet pumping speeds ranging from 1 to 2 m3 s−1 have been measured for operating pressures between 3 and 10 Pa. Deuterium carry-over into the helium exhaust was below the detection limit of the equipment. A design is presented incorporating the cryogenic diffusion pump in a complete fusion reactor forevacuum system, including the separation of impurities from hydrogen isotope mixtures.

The vacuum and gas inlet systems for the RFX fusion experiment

RFX is a large fusion experiment under construction in Padova (Italy). The toroidal vacuum vessel, having a major radius of 2 m and a minor radius of 0.475 m, is built in Inconel 625, and its inner surface is completely covered by 2016 graphite tiles. The residual final pressure should be in the range of 10 −9 mbar; to reach the required vacuum conditions, 12 uhv pumping groups are provided, each of them including one turbo pump (1000l s −1) and one cryogenic pump (1500l s −1). Six forevacuum pump systems, each including one roots pump (double stage) and one rotary pump, assure the regeneration of the cryogenic pumps and the forevacuum conditions for the turbo pumps. The gas inlet system is designed to supply H 2 and D 2 to the vessel in very high purity conditions or in a pre-defined mixture with impurities. The plant control system can work either in manual or automatic mode: in manual mode the system is handled from ‘local operation panels’, whereas in automatic mode it is controlled by a ‘Programmable Logic Controller’ (PLC) which is part of the overall control and monitoring system of the RFX experiment. The paper describes the design of the systems and evidences the main technical solutions that have been adopted.

Experimental set-up for gas balance measurement at JET

The JET experiment (using tritium) has to address the problem of tritium retention in the vessel walls. Therefore, gas balance measurements to assess the first wall behaviour with respect to gas retention and gas release during and after tokamak pulses are already made in the deuterium phase of JET. A pumping system parallel to the standard forevacuum system of JET has been installed to pump and store the discharged gas after each plasma shot. Using a timing sequence to operate valves, the normal mechanical forevacuum pumps are disconnected and a special cryogenic pumping set is used to collect the gas discharged by the torus turbomolecular pumps for a given time after each shot. A storage tank takes the collected gas from the cryogenic pump after a period of operation, from where gas samples can be taken for analysis. This paper describes the set-up, the type of the cryopump and also the various modes of operations of the experimental set-up. The results obtained have shown that the torus walls have a very strong retention capability. Depending on wall surfaces and plasma conditions, release reates between 10 and 80% of the injected gas have been measured.

Mathematical modeling of a cryogenic jet pump with flows of different temperatures

Mathematical modeling of a cryogenic jet pump with flows of different temperatures

Determination of hydrogen in stainless steels by spark-source mass spectrometry

A spark-source mass spectrometric (SSMS) method capable of determining traces of hydrogen in micro-volumes of metals was developed by using a pointed metal probe technique. The hydrogen background was decreased to μg g −1 levels by the combination of a method in which the sample in the ion source is baked under vacuum at 323–343 K for more than 25 ks and a liquid nitrogen or liquid helium cryogenic pump method. This method was applied to the analysis of austenitic stainless steels at μg g −1 hydrogen levels, and the relative standard deviation was within 20% for samples with hydrogen concentrations ranging from 2 to 4 μg g −1. The relative sensitivity coefficent was 2.3 (Fe=1).

Development of a Compact Electron Beam Ion Source Cooled with Liquid Nitrogen

A small-sized EBIS type ion source (mini-EBIS) for production of highly charged ions has been developed. The whole system, namely, the electron gun, ion drift tube, electron collector, ion extraction lens and liquid nitrogen reservoir containing solenoid coil is housed in a vacuum envelope, 150 mmφ in diameter and 500 mm in length. The idea of cooling the solenoid to 77 K has proved very effective to miniaturize the solenoid and its power supply. Moreover, the wall of the liquid nitrogen reservoir exhibits a cryogenic pumping function at the ionization region. In the DC ion extraction mode with an electron current of 15 mA at 2 keV, beam intensities obtained for C6+, N7+, O8+, Ne9+ and Ar16+ ions are at least 5×104, 3×104, 1×104, 5×103 and 3×103 counts per second, respectively.

Cryogenic adsorption of noncondensibles in the high‐vacuum regime

Cryogenic vacuum pumps must use cryogenic adsorption means to remove helium, hydrogen, and neon from vacuum systems in order to achieve high vacuum. The capacity of one such cryosorbent, charcoal, is presented in the form of isosteres of hydrogen and helium in the pressure range 10−7–10−4 Torr and temperature range 10–25 K. Certain important dynamic loading effects related to surface mobility and pore clogging are discussed which can, in high‐flow environments, appreciably affect the apparent capacity of the adsorbent. The implications of the static and dynamic results are discussed in relation to practical aspects of cryopumping, i.e., partial or selective regeneration and optimal cryopumping temperatures.

実証ポロイダルコイル付属冷凍系総合性能試験結果

The Japan Atomic Energy Research Institute (JAERI) is conducting Demonstration Poloidal Coil (DPC) program for investigation of superconducting pulsed-coil technology for fusion. The DPC cryogenic system is designed to cool three forced-cooled superconducting coils being fabricated in this program and the system is composed of newly developed cryogenic circulation pump, cold compressor, and vapor-cooled current leads. The installation of these componets was completed in December of 1987 and the performance test of the whole system was carried out in March, 1988. In this test, we have demonstrated that the cryogenic system meets the specifications for cooling the coil system.

Integrated plasma exhaust cryotransfer and processing for net

Abstract An integrated concept for exhaust pumping, impurity removal, and impurity processing is described. This process is based as far as possible on proven elements, or those under intensive investigation in fusion facilities around the world. The integration of a cryogenic roughing pump with He pump-through (separation) which simplifies the exhaust purification, and total reflux of the electrolyzer products which permits a low-waste clean-up system, are novel process enhancements.

Modulation Doped GaAs with Electron Mobilities Exceeding 107cm2/V sec

AbstractA modulation doped Al.35Ga.65As/GaAs single interface structure using Si delta doping setback from the two dimensional electron gas (2 DEG) by 700Å, was measured in van der Pauw geometry at 0.35K and showed an electron mobility of 1.17× 107 cm2 /V see at a carrier density of 2.2× 1011electrons/cm2. An Al.30Ga.70As/GaAs single quantum-well 250Å wide of similar structure with a 500Å setback yielded a 2 DEG mobility of 5.1× 106 cm2 /Vsec at 3.0×1011 electrons/cm2under similar measurement conditions. These mobilities exceed those previously published by more than a factor of two for the single interface structure, and by nearly an order of magnitude for the quantum-well. The samples were grown by solid source MBE in a Varian Gen II modified with He closed-cycle cryogenic vacuum pumping, and in other ways, to achieve a base pressure of 1.5× 10−12 torr, as measured on a extractor-type ionization gauge that is not subject to the usual x-ray limited reading.

Effectiveness of two parallel cold walls as a cryogenic pumping device.

The effectiveness of parallel plate arrangement as a cryogenic pumping device is examined by use of the direct simulation Monte Carlo method. The arrangement consists of two parallel plates and an end plate. The molecular beam is incident on the 80K plate cooled by liquid nitrogen. Molecules reflected on this plate are then incident on the opposite 20K plate cooled by liquid helium, where most of molecules are condensed. The percentage of non-condensing flux depends on various factors. The effect of the condensation coefficient, the density of incoming stream, and the geometry of the arrangement is examined.

Ion Vapour Deposition

Ion Deposition Ltd is a new company established in Corby, Northamptonshire, as part of the SATRA Group of companies which specialises in international operations in the metals business. IDL has been set up as a specialist coating facility — with the support of the Department of Trade and Industry — initially offering ion vapour deposition of aluminium to, in particular, the Aerospace Industry. Significant investment has been made in equipment and facilities, including the latest state‐of‐art ivadizer from McDonnell Douglas. The vacuum chamber is capable of accepting a component 5ft by 10ft, yet has a barrel coating insert for the processing of large volumes of small parts like rivets and fasteners. The coater is also fitted with the capability of the first cryogenic pumping system, which achieves lower vacuums quickly and efficiently. The IDL plant has been in full operation for seven months, and has already established a firm Aerospace orientated customer base both in the U.K. and mainland Europe. Future plans include the expansion of the Corby facility to include other highly specialised coating services to meet the needs of ‘high tech’ industries in the 1990s'.

Sputtering deposition of thin films at cryogenic temperatures

A sputtering system was adapted to deposit thin films onto substrates that were cryogenically cooled by a two-stage cryorefrigerator acting as a substrate holder. Aluminum films were sputter deposited onto NaCl crystals at various temperatures ranging from 293 down to 40 K. The purpose of this work is to observe composition and microstructural changes resulting from substrate cooling during deposition. Transmission electron microscopy techniques showed that aluminum films deposited using argon onto substrates at 80 K have an f.c.c. structure with a grain size of approximately 300 Å as compared with similar films deposited onto substrates at ambient temperatures which showed grain sizes up to approximately 2000 Å. All the aluminum films deposited at temperatures down to 40 K were found to be microcrystalline rather than amorphous. Sputter-deposited films of aluminum on substrates cooled to 40 K were obtained using neon as the sputter gas with marginal success because of the cryopump's limited capability for maintaining adequate neon flow for optimum sputtering. These films were found to be nodular in appearance with each nodule having a microcrystalline structure with an average grain size of approximately 2000 Å. Low temperature sputter deposition using neon is being investigated with an oil diffusion pump replacing the cryogenic vacuum pump.