Cryopump Research Articles

New automated fill plant opens in America

Team One Technologies, a new industrial gas market distributor, opened its first automated fill plant near Chicago, USA, earlier this year and it chose ACD'S P2K cryogenic pump to be at the heart of its operation.

Tritium Inventories in the High Vacuum Pumps of ITER

ABSTRACTThe tritium inventory of an experimental fusion reactor like ITER is determined by a broad range of influential factors. The tritium retention in the vacuum system is one important contribution to the overall tritium inventory. The high vacuum system for ITER is based on a set of cryogenic pumps, and sees the whole spectrum of tritiated gas species. The cryopumps are accumulation pumps; thus, the semi-permanent tritium inventory present in them is governed by the effectiveness of pump regeneration. Moreover, a permanent inventory background must also be envisaged. This paper delineates the staggered pump concept and a multi-stage regeneration scheme as main measures for step-wise minimisation of the tritium inventory in the high vacuum pump system and outlines the different contributions which add to it. By these methods, the 268 g of tritium inventory present after nominal long pulse operation of ITER, depending on the chosen fuelling case, can be reduced to 6 g in the pumps themselves, plus up to 100 g of codeposited tritium needing recovery clean-up.

Research into Vacuum and Dynamic Characteristics of Cryopanels for Fusion Reactor Ultra-High Vacuum Pumps

ABSTRACTThe present article is devoted to investigation of cryogenic pumping assembly developed at Russian Federal Nuclear Center (VNIIEF). The main scheme of facility is given, where KH-50M pump is a principle unit. The research concerns the pumping speed for the cryopanel cooled to ∼5K, dependent on gas load. The coolant consumption for the selected model of pump is determined.

High output power reluctance electric motors with bulk high-temperature superconductor elements

We present new types of electric machines with the rotors containing bulk high-temperature superconductor (HTS)—YBCO and Bi–Ag—elements. We discuss different schematics of hysteresis, reluctance, ‘trapped field’ and composed synchronous HTS machines. The two-dimensional mathematical models describing the processes in such types of HTS machines were developed on the basis of the theoretical analysis of the electrodynamic and hysteresis processes in the single-domain and polycrystal YBCO ceramic samples and plate shape Bi–Ag elements. We give the test results of the series of hysteresis, reluctance, ‘trapped field’ and composed with permanent magnets HTS motors with an output power rating of 0.1–18 kW and current frequencies 50 Hz and 400 Hz. These results show that in the media of liquid nitrogen the specific output power per one unit weight of the HTS motor is four to seven times better than for conventional electric machines. A comparison of the theoretical and experimental characteristics of the developed HTS motors show that they are in good agreement. We discuss the test results for a liquid nitrogen cryogenic pump system with a hysteresis 500 W HTS motor. We describe several designs of new HTS motors operating in the media of liquid nitrogen with an output power 125 kW (and more) and a power factor of more than 0.8. We discuss future applications of new types of HTS motors for aerospace technology, on-land industry and transport systems.

Operational behaviour of the ASDEX upgrade in-vessel cryo pump

The set-up of the Helium (He) supply circuit for the ASDEX Upgrade cryo pump (CP) with 100 m 3/s Deuterium pumping speed is described together with the key instrumentation and the method of data interpretation. The main peculiarities of the CP operation are the hydraulic instability of the mass flow below 4 g/s, due to large level differences of the transfer line and the sudden heat input of 130 W to the cryo panel during He discharge cleaning of the vacuum vessel. In both cases, a maintenance free, immersed Helium Circulating Pump (HCP), simplifies operation considerably. It permits quick re-filling and re-cooling after He-glowing and stabilisation of the standby mass flow in an oscillatory way down to 2.5 g/s. The measured He losses show that continuous operation of the CP, including He-glowing, is feasible even with a standard 30/60 l/h He-liquifier.

Design Considerations for Cryogenic Pumping Arrays in Spacecraft-Thruster Interaction Facilities

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Low temperature investigations on frictional behaviour and wear resistance of solid lubricant coatings

The tribological characteristics of polymer-based solid lubricant coatings under frictional stressing in vacuum at 293, 120 or 77 K were studied. Vacuum-friction apparatus with cryogenic pumps and low-temperature tribometer designed at SR&DB of ILTP&E was used for sliding tests. It was found that the coefficient of friction is somewhat higher at low than at room temperatures. The effect of temperature decrease on the wear life of solid lubricant coatings is ambiguous and determined by the direction of changes in physical and mechanical characteristics of a solid lubricant coating under cooling and by the rate of the process of a binder tribodestruction.

The recovery and isotopic measurement of water from fluid inclusions in speleothems

The isotopic composition of speleothems is a useful palaeoclimatic indicator, but its value would be enhanced if information on the composition of the parent dripwaters could be recovered from fluid inclusions in the speleothem calcite. To develop a robust method for extracting and measuring oxygen and hydrogen isotopic composition of fluid inclusions we have used anhydrous Iceland Spar and microlitre glass capillaries of water as an analogue system. Crushing the capillary and calcite together in a high vacuum cell we have investigated the adsorbtive and isotopic behaviour of water when exposed to clean fracture surfaces. Significant water adsorption occurs at room temperature, accompanied by large negative isotopic shifts of both oxygen and hydrogen in the recovered free water at H 2O/CaCO 3 mass ratios <10 mg g −1. Cryogenic pumping fails to achieve total desorption. The degree of depletion is inversely related to the water/calcite ratio, fractionation of hydrogen isotopes exceeding −20‰, and oxygen isotopes −10‰, at ratios typically observed in natural speleothems. Heating the crushed calcite at 150°C for 60 min. totally desorbs the water and allows retrieval of the correct isotopic composition. Application of these methods to a British Late Holocene speleothem yields δ 18O and δ 2H compositions for the inclusion water which are closely comparable with the modern cave dripwaters and local precipitation. The results show that isotopic compositions can be recovered from inclusion samples of <1μL (equivalent to approximately 1g of calcite) with precisions that are useful for palaeoclimatic research, ±0.4‰ for δ 18O and ±3‰ for δ 2H. Greater precision than this will require replicate analysis for each speleothem growth increment.

Filling and Recycling Apparatus of a Cyclotron Target with Enriched Krypton for Production of Radiopharmaceuticals

An apparatus for multiple filling of a cyclotron target with enriched Kr gas is described. The system is based on recycling pressurized gas by cryogenic pumping between the target tube and storage containers. The design and construction makes use of previous experience in the construction and operation of two analogue apparatuses for Xe124 high pressure gas targets, but major modifications have been incorporated, evoked by the different physical properties of Kr, by the character of the nuclear reaction, and by the demand for automation from the side of the end user.

Radio-frequency plasma cleaning for mitigation of high-power microwave-pulse shortening in a coaxial gyrotron

Results are reported demonstrating that radio-frequency (rf) plasma cleaning is an effective technique for mitigating microwave-pulse shortening (i.e., lengthening the pulse) in a multimegawatt, large-orbit, coaxial gyrotron. Cleaning plasmas were generated by 50 W of rf power at 13.56 MHz in nitrogen fill gas in the pressure range 15–25 mTorr. Improvements in the averaged microwave energy output of this high-power-microwave device ranged from 15% to 245% for different initial conditions and cleaning protocols. The mechanism for this improvement is believed to be rf plasma sputtering of excess water vapor from the cavity/waveguide and subsequent removal of the contaminant by cryogenic vacuum pumps.

Vacuum, semiconductors and thin film

Varian Ltd has introduced a series of primary vacuum pumps that offer improved reliability and durability. The TriScroll 300 and 600 incorporate dual-scroll, two-stage pumps with the scroll sets operating in series to provide high compression for light gases. The pumps are designed to resist the effects of water vapour, which can cause maintenance problems in scroll pumps. Technical features include pumping speeds of 250 and 500 l min-1 (peak), a low ultimate pressure of ⩽102 Torr, a durable mechanical construction, including a benign tip seal, automatic gas ballast, bearing purge point and improved bearing seals. The pumps should only need to be serviced once a year. The devices are suitable for applications such as loadlocks, PVD systems, primary pummping for turbo-and ion-pumped systems, cryogenic pump roughing and other similar applications that demand a clean, hydrocarbon-free environment.

Noble gas exhaust with a strongly baffled divertor in ASDEX-Upgrade

Since spring of 1997 ASDEX Upgrade has operated with the new divertor II (LYRA), which is characterised by vertical target plates, tight baffling towards the main chamber, and a dome baffle in the private flux region. The main goal of this divertor modification was to increase the divertor density (of the plasma and of the neutrals) for a given plasma density, whereas the neutral density in the main chamber should be similar or even lower. Pumping occurs now from the private flux region which is linked to the pump chamber by finite conductance below the outer target. A cryo pump (about 100 m 3/s) has been installed in the outer divertor chamber in addition to the turbo pumps. This divertor scheme is very similar to the one planned for ITER. First experiments with the new divertor indicate that the compression of helium, C He (the ratio of neutral He density in the divertor to the He density at the plasma edge) is much higher in the new divertor, while the neon exhaust efficiency has decreased. The cryo pump can strongly enhance the scrape-off layer flow of deuterium (by a factor of about 3), resulting in a small improvement of the He exhaust rate.

マイクロ波放電式イオンエンジン用耐久試験装置の開発

In order to take advantage of electric propulsion for a rendezvous with a near-earth small body such as a commet or an asteroid, very long continuous thruster operation of several years is required. For the asteroid sample and return mission named MUSES-C, the institute of space and astronautical science is developing a new-concept ion engine, microwave discharge ion engine, whose cathode-less discharge chamber made the engine being free from the degradation of the electrodes. To demonstrate the new thruster's lifetime, a full-automated test facility was constructed and the endurance test of the ion engine started in February 1997. The facility consists of a large vacuum chamber evacuated by cryogenic pumps and a thruster system; the latter includes a propellant feed system, microwave power generators, power supply units for ion acceleration, and a data acquisition system. All the engine operation system is integrated into a GPIB bus interface and safely controled by computers without any on-site personnel.

An UHV system to study gassing and outgassing of metals under friction

An UHV dynamic expansion system to study gassing and outgassing of metals under friction in vacuum has been developed. The vacuum chamber of the system has two main parts separated by a wall with a central orifice of nominal conductance of 5.27 l s −1 for N 2 at 300 K. The main part of the system is equipped with a quadrupole mass-spectrometer, ion gauge and the gas line supply. The chamber closer to the pumping systems is also equipped with an ion gauge. The pumping of the system is performed by: (I) a turbomolecular and (II) a cryogenic pump, which can operate either independently or in parallel. The ultimate pressure of chambers 1 and 2 are respectively 5.2.10 −11 mbar and 1.10 −9 mbar. The friction cell allocated in chamber 2 consists of a sample holder and a linear motion feedthrough with a steel ball indent allows the friction experiments. The sample holder lets to apply a load to the sample surface with a normal force in the range of 0,02 N to 0,85 N. Heating of the sample up to 500°C is provided by electron bombardment. The temperature of the sample as well as the electrical resistance between the indent and the sample surface can be measured. The results show that pressure increase caused by the deformation of the sealing bellow of the friction cell, i.e. without friction, is 1.7×10 −11 mbar (0.6% of the base pressure). The outgassing of the sample caused by friction depends on the normal force as well as on the sweep frequency. The behavior of the total pressure is characterised by an oscillating current supported on a continuous current, which is not possible to explain at present time.

Results of DIII-D operation with new enabling technologies

Recent experiments on DIII-D have been carried out to understand and explore optimized Tokamak operating modes by exploiting control of the plasma current and pressure profiles using new RF current drive and divertor technology. DIII-D emphasizes plasma shape and divertor experiments using a digital plasma control system and extensive diagnostics to develop improved understanding and control of transport barriers in high performance plasmas. The emphasis of our program is to extend the duration of high performance operating modes beyond the plasma current relaxation time by using ICRF and ECH current drive. Engineering features of the new RF systems being developed for these experiments as well as new divertor results are described. DIII-D employs multi-element ICRF antennas for fast-wave electron heating and on-axis current drive and is beginning 110 GHz ECH experiments with MW-level gyrotrons for off-axis current drive. DIII-D employs active cryogenic divertor neutral particle pumping for plasma density and plasma pressure profile control. A divertor modification is now being implemented on DIII-D to pump higher triangularity plasmas and to better baffle neutral backflow from the recycling divertor region.

Universal crossed molecular beams apparatus with synchrotron photoionization mass spectrometric product detection

Vacuum ultraviolet radiation was generated from an undulator at the Advanced Light Source Synchrotron facility and used for photoionization detection of reaction products in a new universal crossed molecular beams machine. A description of the machine and its performance is presented. Initial experiments on the photodissociation of methylamine (CH3 NH2), ozone (O3), oxalyl chloride [ (OCCl)2] as well as the reactive scattering of Cl with C3 H8 show many of the advantages of photoionization in comparison to electron impact ionization, which has been exclusively used in such instruments in the past. “Momentum matching” of reaction products is much more easily accomplished than in electron impact studies due to suppression of dissociative ionization. The tunability of the vacuum ultraviolet radiation can be used to suppress background from residual gases especially when it is desired to detect free radical reaction products. Even when the tunability cannot be used to suppress background, the fact that little heat is generated by the ionizing beam allows background to be substantially suppressed by cryogenic pumping. The energy resolution of the apparatus is comparable to instruments that have previously been designed with electron impact ionization which have more than twice as long a flight path. This new instrument provides outstanding performance for fundamental studies of chemical dynamics.

Optimization of thermocontrolled tank for hydrogen storage in vehicles

There is growing concern about the environmental pollution caused by vehicular engines and the tendency to replace the dominant liquid hydrocarbon fuels with cleaner alternative energy sources. Hydrogen is a promising alternative to liquid hydrocarbon fuels. It has many advantages when injected directly into the cylinder of an internal combustion engine. However, when using compressed hydrogen gas for automotive applications, large and heavy tanks are required and when used in liquid form, expensive insulating materials and cryogenic pumps are required to create the high pressure. A prototype composite vessel has been developed to supply hydrogen gas at high pressure required for direct injection without compressing gas or using any cryogenic pumps. This vessel, called the thermocontrolled tank has been simulated and then tested to determine the rate of pressure and temperature rise in the tank. The test results indicated that the liquid hydrogen can be brought from atmospheric pressure to the high pressure in a reasonable time period. The composite vessel design has been optimized for use in vehicles. The design problem was formulated as a multi-objective optimization case because of the presence of different conflicting objectives. Weighting factors have been attached to the various objectives and then solved. Conclusions have been drawn from the tests, simulation and optimization results which would allow the most effective storage of hydrogen in thermocontrolled tanks on vehicles equipped with direct gas injection.

Ultrahigh vacuum chemically assisted ion beam etching system with a three grid ion source

A chemically assisted ion beam etching system has been developed which performs high quality, highly anisotropic etching of AlGaAs/GaAs at relatively low ion energies (200 eV). The use of three grid ion optics in a Kaufman ion source allows etching at low energies with reasonable rates without loss of profile verticality. All ultrahigh vacuum etching chamber construction with a high throughput turbomolecular pump and high vacuum loadlock provide routine high quality etching of AlGaAs without the use of etch chamber cryo panels or cryo pumps. Low ion energy and a clean vacuum environment permit the use of a single level, non hard baked photoresist mask. Benefits include high pattern resolution and fidelity, low mask erosion rate, good dimensional control, and easy, complete mask stripping as well as reduced substrate damage.

Local island divertor experiments on CHS

A local island divertor (LID) was installed on the Compact Helical System (CHS) to demonstrate the principle of LID and to study its effects on the edge plasma. The particle flow was observed to be guided to the back side of the externally created magnetic island along field lines, and pumped out by a cryogenic pump with high pumping efficiency. As a result, a factor of about 2 reduction in the average core density was seen compared with non-LID discharges at the same gas puff rate. In addition to the demonstration of these fundamental divertor functions, we observed a modest improvement of energy confinement, which could be due to the edge plasma control by the local island divertor.

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.