Cryosorption Pumping Research Articles

Establishment of a low recycling state with full density control by active pumping of the closed helical divertor at LHD

Superior control of particle recycling and hence full governance of plasma density has been established in the Large Helical Device (LHD) using largely enhanced active pumping of the closed helical divertor (CHD). In-vessel cryo-sorption pumping systems inside the CHD in five out of ten inner toroidal divertor sections have been developed and installed step by step in the LHD. The total effective pumping speed obtained was 67 ± 5 m3 s−1 in hydrogen, which is approximately seven times larger than previously obtained. As a result, a low recycling state was observed with CHD pumping for the first time in LHD featuring excellent density control even under intense pellet fueling conditions. A global particle confinement time () is used for comparison of operation with and without the CHD pumping. The was evaluated from the density decay after the fueling of hydrogen pellet injection or gas puffing in NBI plasmas. A reliably low base density before the fueling and short after the fueling were obtained during the CHD pumping, demonstrating for the first time full control of the particle balance with active pumping in the CHD.

The Economics of Cryosorption Pumping. The Practice of Using a Cryosorption Pump in an Industrial Pumping System

It is shown that in the case of well-developed infrastructure for the use of liquid nitrogen the usage of nitrogen cryosorption pumps (NCP) is significantly more economical compared to the pumping means associated with the use of mechanical and steam jet pumps. The results of preliminary tests of the experimental sample NCP as part of a vacuum unit at the NPO Geliymash confirm the prospects of using NCPs in serial production of cryogenic vessels.

Thermal Transpiration Behavior of Hydrogen Isotopes in Cryogenic Pump System

Cryogenic pumps are convenient machinery for handling hydrogen isotopes in fusion fuel processing systems. Not only ultra-vacuum pumps working at such as liquid helium or hydrogen temperature but also sorption pumps using liquid nitrogen are applicable. The latter type is suitable to a means of temporary storage and/or transportation between process units. In the cryogenic pumping, there is an issue that the pressure in a pump is not necessarily identical with the pressure measured in its evacuating vessel in equilibrium, because of an effect of thermal transpiration. Thermal transpiration is important in adsorption isotherms which characterize cryo-sorption pumping. In this study, the effect of thermal transpiration was investigated for He, H2 and D2 in a closed system consisting of a volume at room temperature and a volume at cryogenic temperature, connected together by a simple narrow pipe or a pipe containing baffle plates as thermal shield. The effect is here described by an equation of nominal-distribution function with respect to the pressure measured in the hot end volume. Defining an effective inner diameter for the latter pipe, agreement is shown of characteristic curves for geometrically different pipes. The error-functional curves for H2 and D2 are agreed together. The curve for He is also perfectly approximated but with a constant shift. This shift results in the difference of a molecular property among He, H2 and D2.

The ITER vacuum systems

ITER is a large vacuum facility which comprises many service, diagnostic and monitoring vacuum sub-systems as well as three large cryogenic pumping systems for evacuation and maintenance of the required pressure levels. Control of the gas throughput is one of the key issues affecting the performance and achievable burn time of a fusion reactor. The main pumping systems are the torus exhaust pumping, the cryopumps for the neutral beam injection systems for plasma heating, and the cryopumps for the ITER cryostat. All customized cryosorption pumps are force-cooled with supercritical helium and share a similar modular design of cryosorption pumping panels. For regeneration of the cryopumps as well as for roughing down the system volumes prior to operation, four identical sets of forepump trains are used. This paper will focus on the areas of the ITER vacuum systems which require customized developments and cannot rely on commercial solutions. The complex pumps have been tailored for the very specific applications and requirements at ITER, especially characterised by the need to be tritium compatible. An outline of the development path which was needed to come up with a sound design for the ITER cryopumps is given. The way of development is culminating in the manufacturing of 1:1 scale prototypes, which will be extensively tested in dedicated test facilities to ensure compatibility with all design requirements.

A road map to extreme high vacuum

Ultimate pressure of a well-designed vacuum system very much depends on pretreatments, processing and procedures [1, 2]. Until now much attention has been paid to minimizing hydrogen outgassing from the vacuum chamber wall materials, however, procedures and processing deserve further scrutiny. For reducing the gas load, high sensitivity helium leak detection techniques with sensitivities better than 1×10−12 Torr l/sec should be used. Effects that are induced by vacuum instrumentation need to be reduced in order to obtain accurate pressure measurements. This paper presents the current status of the CEBAF DC photogun. This state of the art technology is driving the need for Extreme High Vacuum (XHV). We also present sensitive helium leak detection techniques with RGA's, vacuum gauge and RGA calibration procedures, metal sponges for cryosorption pumping of hydrogen to XHV, low cost surface diffusion barriers for reducing the hydrogen gas load and clean assembly procedures. Further, alternative backing pump systems based on active NEGs [3] for turbo molecular pumps are also discussed.

Material compatibility issues in EU fusion fuel cycle R&D and design

Many material selections for fusion Fuel Cycle systems are determined by the properties of tritium, including its behaviour as a hydrogen isotope, and its decay product, 3He. Within the EU R&D program, the following issues related to tritium service have been addressed. The mechanical integrity and longevity of the sorbent/bonding agent/substrate system used for cryosorption pumping have been extensively tested under tritium exposure. Extended testing of palladium/silver membranes used for separation of elemental hydrogens from impurities has been carried out to confirm longevity in tritium service. For all high temperature (∼150 °C) components, tritium permeation through primary containments must be confined by outer (low temperature) jackets, and designs have been developed to achieve this. For wetproof catalysts and solid polymer electrolysers used for water detritiation, tests are in progress to determine the operating life. Testing of the ITER reference tritium storage getter material is under way.

Performance of ITER-Relevant Cryopump Panels for Tritiated Gases

A cryosorption panel test arrangement was installed in the Cryogenic Forevacuum (CF) Subsystem of the Active Gas Handling System (AGHS) at JET. The pump panels were of ITER relevant design in terms of geometry and dimension, coating and sorbent material. The central objective of this investigation was to study, for the first time in such an in-depth and parametric way, the interaction of tritium and tritiated gas mixtures with the panel and the influence on pumping performance and regeneration characteristics. This paper describes how the pump was implemented in the system and summarizes the major experimental results obtained in a two-staged programme: First, the test set-up was used to pump process gases under the Trace Tritium Campaign at JET; secondly, a dedicated test campaign was performed with defined external supply of tritium via a U-bed. It is highlighted that the ITER cryosorption pumping concept achieves highest pumping speeds for tritium. No show-stoppers have been identified.

Pumping characteristics of a cryopump with Ar sorbent in He and in a D2/He mixture

The He generated as a result of D/T burn in a fusion reactor must be exhausted from the plasma to avoid fuel dilution effects. In view of this, transport and exhaust studies of He in fusion plasmas are getting increasing attention in recent years. In fusion plasmas, the exhaust gas will be a combination of D2 and He, with He forming only a small fraction (about 10%). The cryosorption pumping characteristics of pure He and a mixture of D2 and He (90% D2) have been investigated using a cryosorption pump with condensed layers of Ar as sorbent. A cryocondensation pump cooled by liquid He at 4.3 K, and located in the outboard divertor region of the DIII‐D tokamak, was used for the experiment. The investigation was conducted in a pressure regime that is relevant for particle exhaust from fusion plasmas. The experiment revealed that (1) the cryosorption pumping speed of pure He drops precipitously if the Ar/He ratio falls below about 20; (2) the pumping speed for He in a D2/He mixture decreases in an exponential manner with the amount of D2 pumped; (3) increasing the thickness of Ar in the range of 1–12 μm had little effect on the pumping speed for He in a D2/He mixture; and (4) for a pumping surface coated with a thick (≳2 μm) layer of Ar, surrounded by a radiation shield having a transparency factor of about 6, a He pumping speed in the range of 15–25 m3 s−1 m−2 in the mTorr pressure range for a pulse duration of about 5 s can be obtained after pumping about 80 Torr l of D2.

Cryosorption pumping devices

Abstract Based on the experimental studies of the gas cryosorption process a series of cryosorption pumping devices is developed. They are cryosorption pumps cooled by solid nitrogen and liquid helium; a pump for the evacuation of gaseous mixtures enriched by helium; a cryosorption trap and cryosorption elements for in-built pumping systems. Schematic diagrams, construction description, experimental and designed characteristics are presented.

Cryosorption pumping of H 2 and He With Metals and Metal oxides at 4.3 K

Pressures below 10 −10 torr can be maintained in large LHe cooled UHV systemsby increasing the available active cryosorbing surface area. Clean metal oxides (metal sponges) can provide the required surface area increase for higher adsorption capacities as well as for enhancing the pumping speed at extremely low pressures. Metal sponges have several advantages over the conventional cryosorbers viz. molecular sieves and charcoals. The adsorption isotherms of H 2 and He at 4.3 K on metals (Al, stainless steel, Nb) and metal oxides (Al 2O 3, Nb 2O 5) are given here in the pressure range 10 −14 − 10 −6 ton. An extractor gauge is used at LHe temperature to obtain this isotherm data.

Vacuum Sorption Pumping Studies of Argon and Oxygen on 4A Molecular Sieves

Cryosorption pumping is a method of evacuating enclosed volumes by adsorbing gas on a deep bed of sorbent, such as Davison 4A zeolite, at cryogenic temperatures. Modeling the dynamic behavior of these systems for air pumping requires information on two major constituents of air: oxygen and argon. Particle size variation was the major variable in determining the mechanism of the process. The model comprises a fluid-phase mass balance representing the dynamics of gas in the bed and a spherical, one-dimensional diffusion equation describing adsorption in pellets of 4A zeolite. The present model calculates effective pore diffusivity taking into account Knudsen diffusion, ordinary diffusion, and Poiseuille flow. The primary diffusional resistance appears to occur in the macropores formed by the pelletizing clay binder, rather than in the bed interstices or microporous zeolite crystals.

Cryopumping of atomic hydrogen

The pumping speed for the cryopumping of an atomic hydrogen beam was measured. Measurements were made for cryocondensation, cryosorption, and differential pumping. The pumping speed for atomic hydrogen was observed to be much smaller than the pumping speed for molecular hydrogen. It is believed that this is due to the energy released during the recombination of the atomic hydrogen.

7157. Physical vapor deposition equipment evaluation and characterization using statistical methods: VS Dharmadhikar et al, J Vac Sci Technol, A8, 1990, 1603–1607

The authors investigated the possibility of achieving an Extreme High Vacuum (XHV) environment by employing a commercial G-M refrigerator-cooled 10 K cryopump instead of a costly 4 K refrigerator-cooled cryopump. In order to minimize the outgassing rate which might disturb the evaluation of the cryosorption effectiveness in the XHV region, all vacuum walls of the cryopump vessel and the test dome were made of 5052 aluminum alloy the surfaces of which had been specially treated. After 70 days system conditioning, the ultimate pressure (between 3 and 5 × 10−11 Pa) was obtained repeatedly by 3 or 4 days evacuation. The partial pressure behavior of several gases was observed by changing the cryopanel temperature to evaluate the ultimate pressure limit of cryosorption pumping at the relatively higher temperature of 10 K. The experimental result shows that the cryosorption pumping at 10 K is still effective below 10−11 Pa.

Ｇ‐Ｍ冷凍機を用いたクライオポンプによるＸＨＶ実現の可能性

Abstract The authors investigated the possibility of achieving an Extreme High Vacuum (XHV) environment by employing a commercial G-M refrigerator-cooled 10 K cryopump instead of a costly 4 K refrigerator-cooled cryopump. In order to minimize the outgassing rate which might disturb the evaluation of the cryosorption effectiveness in the XHV region, all vacuum walls of the cryopump vessel and the test dome were made of 5052 aluminum alloy the surfaces of which had been specially treated. After 70 days system conditioning, the ultimate pressure (between 3 and 5 × 10 −11 Pa) was obtained repeatedly by 3 or 4 days evacuation. The partial pressure behavior of several gases was observed by changing the cryopanel temperature to evaluate the ultimate pressure limit of cryosorption pumping at the relatively higher temperature of 10 K. The experimental result shows that the cryosorption pumping at 10 K is still effective below 10 −11 Pa.

Capability of obtaining extreme high vacuum by commercial G-M refrigerator-cooled cryopump

The authors investigated the possibility of achieving an Extreme High Vacuum (XHV) environment by employing a commercial G-M refrigerator-cooled 10 K cryopump instead of a costly 4 K refrigerator-cooled cryopump. In order to minimize the outgassing rate which might disturb the evaluation of the cryosorption effectiveness in the XHV region, all vacuum walls of the cryopump vessel and the test dome were made of 5052 aluminum alloy the surfaces of which had been specially treated. After 70 days system conditioning, the ultimate pressure (between 3 and 5 × 10 −11 Pa) was obtained repeatedly by 3 or 4 days evacuation. The partial pressure behavior of several gases was observed by changing the cryopanel temperature to evaluate the ultimate pressure limit of cryosorption pumping at the relatively higher temperature of 10 K. The experimental result shows that the cryosorption pumping at 10 K is still effective below 10 −11 Pa.

Experimental Investigations into Cryosorption Pumping of Plasma Exhaust: Status Report

Within the framework of the European Fusion Technology Programme the Karlsruhe Nuclear Research Centre has been awarded a contract for the development of cryosorption panels for compound cryopumps of the NET plasma exhaust pumping system. This task includes the development of a bonding technique for porous sorbent materials with metal substrates and a test programme for development and optimization of cryopanels. A variety of material combinations for sorbent, bonding and substrate were evaluated and listed in a test matrix. Bonding tests involving soldering, cementing and plasma spraying techniques have been carried out. About 300 sorption specimens have been prepared. The resistance to thermal stress of the sorbent / substrate bond has been studied in thermal cycling tests.

Cryosorption Pumping by Condensed Gas Layer Sorbents

Cryosorption Pumping by Condensed Gas Layer Sorbents

On cryosorption pumping of hydrogen with ZDB-150 type cryopump cooled by a two-stage closed-cycle refrigerator: Bing-kun Liu et al, J Vac Sci Technol, 20 (4), 1982, 1000–1004

On cryosorption pumping of hydrogen with ZDB-150 type cryopump cooled by a two-stage closed-cycle refrigerator: Bing-kun Liu et al, J Vac Sci Technol, 20 (4), 1982, 1000–1004

On cryosorption pumping of hydrogen with the ZDB–150 type cryopump cooled by a two‐stage closed‐cycle refrigerator

The ZDB–150 type cryopump with a 150‐mm i.d. flange, cooled by a two‐stage refrigerator, has been developed for pumping hydrogen, which is the major outgassing product of most metals and the main gas load to be removed in some special applications, such as nuclear fusion. In order to improve the pumping performance of this cryopump for hydrogen, several different configurations and geometries of cryosorption panels were designed and tested. On the other hand, the favorable distribution of the refrigeration capacity and temperature at two cold heads of the refrigerator were also considered and tested. This paper presents the test results on pumping speed and pump capacity for hydrogen with forenamed various considerations. In the selected optimum configuration and condition, the maximum pumping speed and capacity, 2400 l/s and 11 000 Torr⋅l, respectively, were reached. It was concluded that enhancing the pumping capability of cryopump for hydrogen is potentially feasible.

Cryosorption pumping

Cryosorption pumping