Design Of Cryopumps Research Articles

Heat transfer enhancement of NBI vacuum pump cryopanels

Huge cryogenic pumps are installed inside neutral beam injectors in order to manage the typically very large gas flows. This paper deals with the aspect of passive cooling in NBI cryopump design development and discusses design considerations in two example areas. One is the design of cryopanels consisting of a pipe, centrally supplied with cryogenic helium, and a welded fin, passively cooled, to provide the necessary pumping surface below a given maximum temperature. The results of several parametric simulations in ANSYS are presented using different copper thicknesses and cryopanel geometries to discuss the thermal capability (heat transfer characteristics and heat capacities) of a number of design variants. The optimum design solution is based on copper-coated fins, using an electroplating technique, and thereby improving the heat transfer of the cryopanels while attaining an overall reduction in weight. The other area is the sound design of the manifold shielding system with a weld contact between copper and stainless steel. Weld samples were manufactured and investigated to raise awareness of the demands and risks during manufacturing and to demonstrate that readily applicable weld procedures exist.

Cryopump design for the ITER heating neutral beam injector

Forschungszentrum Karlsruhe (FZK) is developing cryopumps for ITER heating neutral beam injectors (NBIs). The system is characterized by high gas flows coming from different sources against which the cryopumps must maintain a pressure between 10−2 and 10−3 Pa in the beam line (BL) vessel. The design of 2001 had proposed a cylindrical vessel with a cylindrical cryopump inside with a maximized pumping area to cover the vacuum requirements. In this design the only access to all BL components was through the beam source vessel, making it necessary to dismantle the beam source for all maintenance issues on the BL. During the ongoing design investigations on the heating NBI, it was decided in 2006 to use a rectangular vessel for the BL with a top access to improve the maintenance. This necessitated a full redesign of the cryopumps. In the new geometry of the BL vessel the size of the cryopump is limited to a flat rectangular geometry of 8 m length, 2.75 m height and 0.5 m depth. To cover the vacuum requirements two cryopumps of this size must be included for each injector. Gas profile calculations using the detailed BL geometry have been used to detect the needed gas capture probability of the pumping surface to guarantee the beam pulse operation. In this paper we give an outline of the working scope done to come up with a cryopump design covering the needs of the ITER NBI. The design of the novel cryopump and the heat load calculations for the different operation scenarios will be discussed. It is shown that the cryopump for the ITER heating NBI covers all vacuum requirements and it is fully adapted to the ITER cryogenic supply.

Cryopump design development for the ITER Neutral Beam Injectors

Forschungszentrum Karlsruhe (FZK) is developing the cryopumps for the ITER Neutral Beam Injectors (NBI). The system is characterized by high gas flows against which the cryopumping system must maintain the required pressures down to 10 −3 Pa in the beam line vessel. During detailed investigations of the gas dynamics in the neutral beam system it showed up that in the close geometry of the beam line design a cryopump with a gas capture probability of 30% is needed to cover the low pressures. This cannot be achieved by a classical cryopump design using a chevron baffle because it is limited to gas capture probabilities below 24%. Therefore, a novel cryopump has been developed which is characterised by a gas capture probability of 33%. The engineering design of the pump takes into account that it will be operated under the conditions of the ITER cryosupply. Under these conditions the heat load to the low temperature circuits of the new cryopump design is only 20% higher than for the classical cryopump which is in regard of the 50% higher pumping speed a very good improvement of the entire efficiency. The new cryopump design is now the reference design for the ITER Heating NBI. Two cryopumps will be integrated in the beam line vessel, each of them about 8 m long and 2.75 m high resulting in an overall pumping speed for hydrogen (H 2) of 5000 m 3 s −1. This paper describes the vacuum conditions of the ITER Heating NBI and summarizes the pumping properties of the cryosorption pump as well as to the investigations on the heat loads to the cryogenic circuits.

Design of cryosorption pumps for TEST BEDS of ITER relevant Neutral Beam Injectors

Abstract This paper presents the results of the design investigations and the manufacturing of cryosorption pumps for the Neutral Beam Test Facility ‘MANITU’ at Max Planck Institute for Plasma Physics (IPP) and the cryopump design analyses performed for the development of a test facility for the first ITER Neutral Beam Injector. The two identical cryopumps for IPP are foreseen to pump a hydrogen-throughput of 3 Pa m 3 /s (H 2 ) with a pumping speed of 350 m 3 /s per pump. The pressure conditions must be maintained over 4 h pumping without regeneration of the cryopanels. For the ITER Neutral Beam Test Facility, design calculations to assess heat loads and pumping parameters of the cryopumps will be briefly described.

Structural Analysis and Calculation for the Radiation Baffle of Cryopumps

To decrease the radiation heat load of the cryopanel is considered to be necessary for the design of cryopumps. In general, a radiation baffle is mounted between the cryopanel and the heat source. The radiation baffle absorbs the majority of the radiated heat load. However, the motion of molecules to be pumped is baffled and the pumping speed is lowered at the same time. Therefore the selection of a good radiation baffle is a very important issue for the economical operation of the cryopump. By calculating and comprehensively analyzing the thermal transmission coefficients and the molecular transmission coefficients of baffles of different structures, a type of Chevron baffle is found to be more satisfactory. This paper focuses on the application of the Monte Carlo Method involved in the process of analysis and calculation.

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.

4898. Cryopumped beam mass spectrometry: J Visser, J Vac Sci Technol, 19 (1), 1981, 104–108

Forschungszentrum Karlsruhe (FZK) is developing the cryopumps for the ITER Neutral Beam Injectors (NBI). The system is characterized by high gas flows against which the cryopumping system must maintain the required pressures down to 10−3 Pa in the beam line vessel. During detailed investigations of the gas dynamics in the neutral beam system it showed up that in the close geometry of the beam line design a cryopump with a gas capture probability of 30% is needed to cover the low pressures. This cannot be achieved by a classical cryopump design using a chevron baffle because it is limited to gas capture probabilities below 24%.Therefore, a novel cryopump has been developed which is characterised by a gas capture probability of 33%. The engineering design of the pump takes into account that it will be operated under the conditions of the ITER cryosupply. Under these conditions the heat load to the low temperature circuits of the new cryopump design is only 20% higher than for the classical cryopump which is in regard of the 50% higher pumping speed a very good improvement of the entire efficiency. The new cryopump design is now the reference design for the ITER Heating NBI. Two cryopumps will be integrated in the beam line vessel, each of them about 8 m long and 2.75 m high resulting in an overall pumping speed for hydrogen (H2) of 5000 m3 s−1.This paper describes the vacuum conditions of the ITER Heating NBI and summarizes the pumping properties of the cryosorption pump as well as to the investigations on the heat loads to the cryogenic circuits.

Experimental performance of an open structure cryopump

The Joint European Torus (JET) will utilize neutral injection as a form of additional heating. One important aspect of the neutral injector is the requirement of a large scale pumping system to handle ∼ 250 torr / s −1 of H 2 and D 2 gas with pumping speeds of up to 10 7 / s −1. With existing technology, the only economical way to provide the necessary pumping speed is by means of liquid helium condensation cryopumps. A major problem in the design of cryopumps is that of reducing thermal loading on the helium surfaces whilst maintaining adequate conductance for gas molecules. To achieve the required pumping speed within the space limitations of the JET injector, a ‘Serial Open Structure (Four Stage)’ pump has been designed and is at present being manufactured. The design aims to provide roughly twice the speed of the conventional chevron pump. The compact Open Structure concept, which also lends itself to ease of fabrication, has been checked experimentally on a single stage model cryopump (pumping speed for H 2 ∼ 60,000 / s −1. In this paper we describe this experimental work, the results of which, together with theoretical design calculations, formed the design basis for the final JET Serial Open Structure. A relative comparison of pumping speed, thermal loading and also performance in the presence of an energetic particle beam (7 amps at 50 keV) has been made with a conventional chevron pump under identical test conditions.

Molecular and radiation transmissivities of chevron type baffles for cryopumping

In the design of cryopumps, intermediate temperature (e.g. 77 K) baffles are interposed between the cold pumping surfaces and ambient temperature walls of the vacuum system. This intermediate baffle serves to reduce the effects of thermal radiation on the pumping surfaces. The introduction of the baffle, however, decreases the pumping speed, and therefore its design has to be optimized with respect to both molecular and radiation transparencies. We have studied the transmission probabilities for molecules and photons, assuming diffuse and specular reflection, respectively, as a function of the geometry and surface reflectivity of chevron type baffles, using the Monte Carlo method. The calculated figures are in good agreement with experimental results. Using a black paint which provides a reflectivity of ∠0.10, a molecular transmissivity of about 0.24 and a radiation transmissivity of ∠7×10−4 were achieved.

Effects of thermal spikes on the characteristics of cryosorption pumps with condensed carbon dioxide layers

Forschungszentrum Karlsruhe (FZK) is developing the cryopumps for the ITER Neutral Beam Injectors (NBI). The system is characterized by high gas flows against which the cryopumping system must maintain the required pressures down to 10−3 Pa in the beam line vessel. During detailed investigations of the gas dynamics in the neutral beam system it showed up that in the close geometry of the beam line design a cryopump with a gas capture probability of 30% is needed to cover the low pressures. This cannot be achieved by a classical cryopump design using a chevron baffle because it is limited to gas capture probabilities below 24%.Therefore, a novel cryopump has been developed which is characterised by a gas capture probability of 33%. The engineering design of the pump takes into account that it will be operated under the conditions of the ITER cryosupply. Under these conditions the heat load to the low temperature circuits of the new cryopump design is only 20% higher than for the classical cryopump which is in regard of the 50% higher pumping speed a very good improvement of the entire efficiency. The new cryopump design is now the reference design for the ITER Heating NBI. Two cryopumps will be integrated in the beam line vessel, each of them about 8 m long and 2.75 m high resulting in an overall pumping speed for hydrogen (H2) of 5000 m3 s−1.This paper describes the vacuum conditions of the ITER Heating NBI and summarizes the pumping properties of the cryosorption pump as well as to the investigations on the heat loads to the cryogenic circuits.

902. Stirling cryogenerators and cryopumping: G J Haarhuis,Vide, 29 (171–172), 1974, 351–354

Forschungszentrum Karlsruhe (FZK) is developing the cryopumps for the ITER Neutral Beam Injectors (NBI). The system is characterized by high gas flows against which the cryopumping system must maintain the required pressures down to 10−3 Pa in the beam line vessel. During detailed investigations of the gas dynamics in the neutral beam system it showed up that in the close geometry of the beam line design a cryopump with a gas capture probability of 30% is needed to cover the low pressures. This cannot be achieved by a classical cryopump design using a chevron baffle because it is limited to gas capture probabilities below 24%.Therefore, a novel cryopump has been developed which is characterised by a gas capture probability of 33%. The engineering design of the pump takes into account that it will be operated under the conditions of the ITER cryosupply. Under these conditions the heat load to the low temperature circuits of the new cryopump design is only 20% higher than for the classical cryopump which is in regard of the 50% higher pumping speed a very good improvement of the entire efficiency. The new cryopump design is now the reference design for the ITER Heating NBI. Two cryopumps will be integrated in the beam line vessel, each of them about 8 m long and 2.75 m high resulting in an overall pumping speed for hydrogen (H2) of 5000 m3 s−1.This paper describes the vacuum conditions of the ITER Heating NBI and summarizes the pumping properties of the cryosorption pump as well as to the investigations on the heat loads to the cryogenic circuits.

896. The evolution from regular to irregular motion of ionization waves in neon: J Krása et al,J Phys D: Appl Phys, 7 (18), 1974, 2541–2544

Forschungszentrum Karlsruhe (FZK) is developing the cryopumps for the ITER Neutral Beam Injectors (NBI). The system is characterized by high gas flows against which the cryopumping system must maintain the required pressures down to 10−3 Pa in the beam line vessel. During detailed investigations of the gas dynamics in the neutral beam system it showed up that in the close geometry of the beam line design a cryopump with a gas capture probability of 30% is needed to cover the low pressures. This cannot be achieved by a classical cryopump design using a chevron baffle because it is limited to gas capture probabilities below 24%.Therefore, a novel cryopump has been developed which is characterised by a gas capture probability of 33%. The engineering design of the pump takes into account that it will be operated under the conditions of the ITER cryosupply. Under these conditions the heat load to the low temperature circuits of the new cryopump design is only 20% higher than for the classical cryopump which is in regard of the 50% higher pumping speed a very good improvement of the entire efficiency. The new cryopump design is now the reference design for the ITER Heating NBI. Two cryopumps will be integrated in the beam line vessel, each of them about 8 m long and 2.75 m high resulting in an overall pumping speed for hydrogen (H2) of 5000 m3 s−1.This paper describes the vacuum conditions of the ITER Heating NBI and summarizes the pumping properties of the cryosorption pump as well as to the investigations on the heat loads to the cryogenic circuits.

The Optimization of a Tubular Condensation Cryopmp for Pressures below 10-13 Torr

Over the last few years a condensation cryopump was developed at CERN and successfully applied to one crossing region of the Intersecting Storage Rings for protons. Pressures in the 10-13 torr range were achieved. The major limitation of this pump is that the H2 degassing from the 300 K walls of the pump prevents the achievement of pressures below 10-13 torr, even though the degassing rate of the stainless steel is 2×10-13 torr l/cm2 sec. Herein a cryopump design of tubular geometry is presented, which incorporates in its vacuum system only a very small fraction of ambient temperature walls, greatly reducing the previous limitation. Furthermore, the total amount of the 300 K radiation reaching the cold baffles is reduced by about two orders of magnitude. This has the double advantage that the baffles can be cooled at lower temperatures and can be allowed to be more “transparent” to radiation and hence to molecules. The new model has been entirely optimised both for molecular and radiation transmission by a Monte Carlo method. It is designed to have a pumping speed of 3000 l s-1 for H2 at the two entrances, an axial conductance providing a pressure drop across the pump of a factor of ten and a limit pressure in the 10-14 torr range.

1166. Complex study of the secondary-emission properties of vacuum-melted copper

Forschungszentrum Karlsruhe (FZK) is developing the cryopumps for the ITER Neutral Beam Injectors (NBI). The system is characterized by high gas flows against which the cryopumping system must maintain the required pressures down to 10−3 Pa in the beam line vessel. During detailed investigations of the gas dynamics in the neutral beam system it showed up that in the close geometry of the beam line design a cryopump with a gas capture probability of 30% is needed to cover the low pressures. This cannot be achieved by a classical cryopump design using a chevron baffle because it is limited to gas capture probabilities below 24%.Therefore, a novel cryopump has been developed which is characterised by a gas capture probability of 33%. The engineering design of the pump takes into account that it will be operated under the conditions of the ITER cryosupply. Under these conditions the heat load to the low temperature circuits of the new cryopump design is only 20% higher than for the classical cryopump which is in regard of the 50% higher pumping speed a very good improvement of the entire efficiency. The new cryopump design is now the reference design for the ITER Heating NBI. Two cryopumps will be integrated in the beam line vessel, each of them about 8 m long and 2.75 m high resulting in an overall pumping speed for hydrogen (H2) of 5000 m3 s−1.This paper describes the vacuum conditions of the ITER Heating NBI and summarizes the pumping properties of the cryosorption pump as well as to the investigations on the heat loads to the cryogenic circuits.

1159. The design, construction and performance of a caesium-beam tube

Forschungszentrum Karlsruhe (FZK) is developing the cryopumps for the ITER Neutral Beam Injectors (NBI). The system is characterized by high gas flows against which the cryopumping system must maintain the required pressures down to 10−3 Pa in the beam line vessel. During detailed investigations of the gas dynamics in the neutral beam system it showed up that in the close geometry of the beam line design a cryopump with a gas capture probability of 30% is needed to cover the low pressures. This cannot be achieved by a classical cryopump design using a chevron baffle because it is limited to gas capture probabilities below 24%.Therefore, a novel cryopump has been developed which is characterised by a gas capture probability of 33%. The engineering design of the pump takes into account that it will be operated under the conditions of the ITER cryosupply. Under these conditions the heat load to the low temperature circuits of the new cryopump design is only 20% higher than for the classical cryopump which is in regard of the 50% higher pumping speed a very good improvement of the entire efficiency. The new cryopump design is now the reference design for the ITER Heating NBI. Two cryopumps will be integrated in the beam line vessel, each of them about 8 m long and 2.75 m high resulting in an overall pumping speed for hydrogen (H2) of 5000 m3 s−1.This paper describes the vacuum conditions of the ITER Heating NBI and summarizes the pumping properties of the cryosorption pump as well as to the investigations on the heat loads to the cryogenic circuits.

667. A getter ion pump: A S Nazarov, USSR Patent 184,389, Appril 14 thApril 1965, Publ 10 thSept 1966

Forschungszentrum Karlsruhe (FZK) is developing the cryopumps for the ITER Neutral Beam Injectors (NBI). The system is characterized by high gas flows against which the cryopumping system must maintain the required pressures down to 10−3 Pa in the beam line vessel. During detailed investigations of the gas dynamics in the neutral beam system it showed up that in the close geometry of the beam line design a cryopump with a gas capture probability of 30% is needed to cover the low pressures. This cannot be achieved by a classical cryopump design using a chevron baffle because it is limited to gas capture probabilities below 24%.Therefore, a novel cryopump has been developed which is characterised by a gas capture probability of 33%. The engineering design of the pump takes into account that it will be operated under the conditions of the ITER cryosupply. Under these conditions the heat load to the low temperature circuits of the new cryopump design is only 20% higher than for the classical cryopump which is in regard of the 50% higher pumping speed a very good improvement of the entire efficiency. The new cryopump design is now the reference design for the ITER Heating NBI. Two cryopumps will be integrated in the beam line vessel, each of them about 8 m long and 2.75 m high resulting in an overall pumping speed for hydrogen (H2) of 5000 m3 s−1.This paper describes the vacuum conditions of the ITER Heating NBI and summarizes the pumping properties of the cryosorption pump as well as to the investigations on the heat loads to the cryogenic circuits.

Remarks on measuring the ultimate pressure of high vacuum pumps: R Buhl and O Winkler,Vacuum, 16 (12), Dec 1966, 695–696

This paper presents the results of the design investigations and the manufacturing of cryosorption pumps for the Neutral Beam Test Facility ‘MANITU’ at Max Planck Institute for Plasma Physics (IPP) and the cryopump design analyses performed for the development of a test facility for the first ITER Neutral Beam Injector.The two identical cryopumps for IPP are foreseen to pump a hydrogen-throughput of 3 Pa m3/s (H2) with a pumping speed of 350 m3/s per pump. The pressure conditions must be maintained over 4 h pumping without regeneration of the cryopanels. For the ITER Neutral Beam Test Facility, design calculations to assess heat loads and pumping parameters of the cryopumps will be briefly described.

743. Corrosion in mercury diffusion pumps: E W Gooden, “Corrosion in transport and industry”, 6th Ann Conf Australasian Corrosion Assoc, 15–19 Nov 1965, 6 pages

Forschungszentrum Karlsruhe (FZK) is developing the cryopumps for the ITER Neutral Beam Injectors (NBI). The system is characterized by high gas flows against which the cryopumping system must maintain the required pressures down to 10−3 Pa in the beam line vessel. During detailed investigations of the gas dynamics in the neutral beam system it showed up that in the close geometry of the beam line design a cryopump with a gas capture probability of 30% is needed to cover the low pressures. This cannot be achieved by a classical cryopump design using a chevron baffle because it is limited to gas capture probabilities below 24%.Therefore, a novel cryopump has been developed which is characterised by a gas capture probability of 33%. The engineering design of the pump takes into account that it will be operated under the conditions of the ITER cryosupply. Under these conditions the heat load to the low temperature circuits of the new cryopump design is only 20% higher than for the classical cryopump which is in regard of the 50% higher pumping speed a very good improvement of the entire efficiency. The new cryopump design is now the reference design for the ITER Heating NBI. Two cryopumps will be integrated in the beam line vessel, each of them about 8 m long and 2.75 m high resulting in an overall pumping speed for hydrogen (H2) of 5000 m3 s−1.This paper describes the vacuum conditions of the ITER Heating NBI and summarizes the pumping properties of the cryosorption pump as well as to the investigations on the heat loads to the cryogenic circuits.

713. Exo-electron emission from abraded metal surfaces at high and ultrahigh vacuum: J A Ramsey, J Appl Phys, 37(1), Jan 1966, 452

Forschungszentrum Karlsruhe (FZK) is developing the cryopumps for the ITER Neutral Beam Injectors (NBI). The system is characterized by high gas flows against which the cryopumping system must maintain the required pressures down to 10−3 Pa in the beam line vessel. During detailed investigations of the gas dynamics in the neutral beam system it showed up that in the close geometry of the beam line design a cryopump with a gas capture probability of 30% is needed to cover the low pressures. This cannot be achieved by a classical cryopump design using a chevron baffle because it is limited to gas capture probabilities below 24%.Therefore, a novel cryopump has been developed which is characterised by a gas capture probability of 33%. The engineering design of the pump takes into account that it will be operated under the conditions of the ITER cryosupply. Under these conditions the heat load to the low temperature circuits of the new cryopump design is only 20% higher than for the classical cryopump which is in regard of the 50% higher pumping speed a very good improvement of the entire efficiency. The new cryopump design is now the reference design for the ITER Heating NBI. Two cryopumps will be integrated in the beam line vessel, each of them about 8 m long and 2.75 m high resulting in an overall pumping speed for hydrogen (H2) of 5000 m3 s−1.This paper describes the vacuum conditions of the ITER Heating NBI and summarizes the pumping properties of the cryosorption pump as well as to the investigations on the heat loads to the cryogenic circuits.

744. Experiments with a liquid helium cryopumped extreme high vacuum: R W Moore, Jr, Sixth Annual Symposium on Space Environmental Simulation, St Louis, Missouri, May 1965, 17 pages

Forschungszentrum Karlsruhe (FZK) is developing the cryopumps for the ITER Neutral Beam Injectors (NBI). The system is characterized by high gas flows against which the cryopumping system must maintain the required pressures down to 10−3 Pa in the beam line vessel. During detailed investigations of the gas dynamics in the neutral beam system it showed up that in the close geometry of the beam line design a cryopump with a gas capture probability of 30% is needed to cover the low pressures. This cannot be achieved by a classical cryopump design using a chevron baffle because it is limited to gas capture probabilities below 24%.Therefore, a novel cryopump has been developed which is characterised by a gas capture probability of 33%. The engineering design of the pump takes into account that it will be operated under the conditions of the ITER cryosupply. Under these conditions the heat load to the low temperature circuits of the new cryopump design is only 20% higher than for the classical cryopump which is in regard of the 50% higher pumping speed a very good improvement of the entire efficiency. The new cryopump design is now the reference design for the ITER Heating NBI. Two cryopumps will be integrated in the beam line vessel, each of them about 8 m long and 2.75 m high resulting in an overall pumping speed for hydrogen (H2) of 5000 m3 s−1.This paper describes the vacuum conditions of the ITER Heating NBI and summarizes the pumping properties of the cryosorption pump as well as to the investigations on the heat loads to the cryogenic circuits.