Non-evaporable Getter Pumps Research Articles

Design and pumping characteristics of a compact titanium–vanadium non-evaporable getter pump

A compact non-evaporable getter (NEG) pump is made by stacking sintered titanium–vanadium blades recently available from SAES Getters as St185. The 50 blades are stacked between copper spacers on a stainless steel tube, and are activated by a removable heater cartridge inserted into the tube. The room temperature pumping speeds for CO and N2 are measured as a function of sorbed gas quantities at various activation temperatures and with different NEG disk spacing, in order to optimize the pump design and operation. The study shows that there is a threshold of activation at a temperature of about 340 °C and optimal pumping speed and pumping capacity can be achieved with activation temperature around 550 °C. Linear pumping speeds of about 2200 l/s m and 1300 l/s m can be achieved for CO and N2, respectively, with activation at temperatures of 500 °C for 1 h. A direct comparison shows a much higher pumping speed for the St185 than that for the St707 (Zr–V–Fe alloy, also by SAES Getters). The low activation temperature of the St185 NEG and the compact design make the NEG pump cartridge particularly attractive for situations with tight space and with components sensitive to high temperature.

Combination of a cryopump and a non-evaporable getter pump in applications

A preliminary study on the pumping performance of a cryopump combined with a high-capacity non-evaporable getter (NEG) pump was performed. The pumping speed, the pump-down time, and the gas composition in a standard UHV chamber were evaluated using the cryopump alone and combined with a high capacity getter pump made from sintered porous getter material. In order to exploit the high specificity of the getter pump for hydrogen and water vapor, the cited quantities were measured both before and after a baking treatment. It was found that the ultimate pressure in the baked chamber could be greatly improved using the getter pump and that pump-down times of the unbaked chamber were consistently reduced due to the very high pumping speed of NEGs for water vapor.

Design of the vacuum system for the elliptical multipole wiggler at the Advanced Photon Source

A vacuum system for the Advanced Photon Source elliptical multipole wiggler (EMW) that will operate at a pressure of 10−9 Torr with a storage ring current of 100 mA at 7.0 GeV has been designed and is being fabricated. The major part of the system is a stainless steel chamber with a 66.6 mm by 19.6 mm rectangular cross section. The length of the vacuum chamber is 3100 mm, and the wall thickness is 1.2 mm. Two versions of the vacuum chamber will be produced: with and without distributed nonevaporable getter (NEG) pumping. The version with NEG pumping will have slides on the top and bottom walls to accommodate sintered plates available from SAES. To activate these plates, the entire vacuum chamber will be baked from the outside up to a temperature of 350° C–450 °C. Provision for the baking is included in the design of the vacuum system, its support, and in the EMW itself. The complexity introduced into the design by the need for external activation of the NEG plates is eliminated in the design of the second version of the chamber. In this chamber, a sufficiently low outgassing rate may be achieved by extensive surface cleaning and baking in a vacuum furnace (10−6 Torr) up to a temperature of 950 ° C as has been achieved at the ESRF. Both versions are being pursued in parallel.

Experience with the use of a turbomolecular pump combined with a NEG pump in UHV conditions

The use of turbomolecular pumps is widely diffused in HV and UHV applications. However in UHV conditions, where hydrogen is usually the dominant species, the performances of turbomolecular pumps tend to decay due to their poor pumping ability or compression ratio for this gas. Therefore their combination with the non-evaporable getter (NEG) pumps, which is much more efficient for hydrogen, appears an interesting solution in order to achieve a better vacuum in the low pressure region. The synergistic effect of the two types of pumps has been investigated here through specific tests, with the NEG pump suitably located in a vacuum system equipped with a turbomolecular pump. The results obtained, in terms of pumping speed, ultimate pressure achieved and hints on gas composition, are described here and discussed. They show that the final pressure can be reduced by two orders of magnitude, from 10 −9 to 10 −11 mbar in the test chamber, when a NEG pump is used in conjunction with the turbomolecular pump, compared with the turbomolecular pump alone.

Vacuum system for the storage of molecular ions at the cooler ring TARN-II

A light and heavy ion synchrotron with an electron cooling system, TARN-II, has been operated for the studies of atomic physics and accelerator technology. After the upgrading of the pump system by adding ion pumps and titanium getter pumps in 1991, and non-evaporable getter pumps based on St 707 in 1994, an average pressure of the order of 10 −9 Pa has been achieved. Molecular ion beams such as H 2 +, H 3 +, HD +, HD 2 +, HeH + and HeD + have been stored in the ring for the experiments of collision between molecular ions and electrons. A beam life time of 5 s was measured for HD + ions at an average pressure of 7 × 10 −9 Pa. The performance of the system is presented.

Some important developments in capture pumping technology in the last 40 years

Highlights of the history of capture pumping technology are given. The subjects covered include some of the important chronological developments in sputter-ion, electrostatic-ion, sublimation, nonevaporable getter, and cryogenic pumping in the last 40 years. All of these forms of pumps proved to be essential tools for the attainment of ultrahigh vacuum.

XHV System for Surface Analysis Using a New Getter to Reduce Hydrogen.

For almost the past two decades, surface analysis instruments have maintained an UHV environment which is achieved by UHV pumps. Recently, the XHV environment has been required in surface analysis, but an instrument which has many parts in a vacuum is eventually limited in the baking temperature. To achieve an XHV environment in a surface analysis instrument, H2 is the key component. Thus we tested a nonevaporable getter pump to reduce the amount of H2 and we have measured the residual mass spectrum in a practical instrument using a low outgassing rate mass spectrometer. We obtained a low range of 10-9 Pa using the NEG pump and conventional pumps with relatively low baking temperature. The ion source of the sputter-etching gun was mainly the outgassing of H2 under operating conditions, and hence the pumping speed was not sufficient to maintain the amount of H2 from the ion gun.

Pumping Characteristics of Zr-V-Fe Nonevaporable Getter In Mixture of H2 and CO Gases.

The effect of impure gases on the vacuum performance of a Zr-V-Fe nonevaporable getter (NEG) module were investigated using a gas mixture composed of 80% H2 and 20% CO to simulate a practical vacuum environment. Pumping speeds for H2 and CO in the mixture were measured simultaneously and continuously with two quadrupole mass analyzers in a standard test dome. The pumping speed for H2 was strongly influenced by CO molecules absorbed on the surface of the NEG, while that of CO was nearly independent of H2 absorbed in the NEG. The H2 pumping speed in the mixture with CO was changed very steeply, similarly to that of CO.It is expected that the results of the mixed gas experiment will be utilized to devise a proper operation schedules of the NEG pumps installed in the SPring-8 storage ring.

Water vapour sorption characteristics of a non-evaporable getter pump

Non-evaporable getter pumps are widely used in applications in the uhv range where hydrogen and carbon monoxide are the dominant gases, but they can find equally satisfactory use in poorly baked systems where water vapour is not a negligible part of the residual atmosphere. While literature data generally refer to basic kinetics and mechanisms of water sorption on getter materials, lack of data exist about the overall sorption characteristics of complex structures like a getter cartridge. An experimental system has been set up in which the factors possibly affecting a sorption test for water vapour have been minimized. Water vapour sorption curves have been determined on a NEG pump in a pressure range below 10 −4 mbar and are presented to show pumping speed vs sorbed quantity at different temperatures. A comparison with the sorption curves for other gases (CO, H 2) is also discussed.

Further development of the CELSIUS uhv system

The cluster-jet target assembly and several other parts of the vacuum system have gone through a major reconstruction to fulfill the needs of some approved physics experiments in the ring. Specially designed Non-Evaporable Getter (NEG) pump modules have been developed and installed in the electron cooler. To cope with the heavy gas load from a hydrogen pellet target, which is now being developed, further NEG modules are considered, combined with cryopumps for differential pumping around the pellet target.

Lumped NEG pump for crotch and pumping system of SPring-8 storage ring

A prototype of the lumped NEG pump (LNP) designed as a main pump of the crotches and absorbers of the storage ring was manufactured with 14 nonevaporable getter (NEG) modules and a cylindrical pump body made of an aluminum alloy. Vacuum performance and operating characteristics of the LNP have been tested. Initial pumping speeds of the LNP for H 2, CO, N 2 and CO 2 were typically 3m 3 s −1, 1.7 m 3 s −1, 1 m 3 s −1 and 1.3 m 3 s −1, respectively. The experimental results were compared with pumping speeds calculated by the Monte Carlo method. The pumping speed of the practical LNP to be installed in the storage ring was also calculated. The pumping system, which is composed of these LNPs and NEG strips to be installed in the vacuum chambers, was described. Based on this pumping system, the calculated pressure profile of the storage ring is also presented.

Historical perspective of vacuum system application at the Nevada Test Site

From the beginning of nuclear-device testing at the Nevada Test Site (NTS) in 1951 to the present, the U. S. Nuclear weapons laboratories have used high-vacuum environment in a wide range of applications. Nuclear measurement and diagnostic devices used in the test procedures require vacuum levels from 10−1 to less than 10−7 Torr. Researchers also need these vacuum levels to control the experimental environment when they study the effects of nuclear weapons on materials, devices, structures, or weapon system components. To produce the required vacuum environments in volumes up to 107 ℓ, researchers have used the following pumping systems: simple pumping apparatus, such as oil-sealed, rotary-vane mechanical pumps (pumping speeds as low as 2 ℓ/s); conventional, multistage, cascade pumping arrangements of oil diffusion, Roots blowers, and high-speed mechanical pumps (pumping speeds greater than 100 000 ℓ/s); and state-of-the-art, high-speed cryogenic, sputter-ion, turbomolecular, and evaporable or nonevaporable getter pumps (pumping speeds from 10 to more than 30 000 ℓ/s). More often, these pumping systems are remote from their operational control points. This paper describes these high-reliability vacuum systems and their engineering, design, and fabrication.

Combined sputter-ion and NEG pump

The combination of Non-Evaporable Getter (NEG) material with sputter-ion pumps allows the design of a highly compact and reliable uhv-pump with remarkable high pumping speed for active gases. A unique heater concept for the activation of the NEG material overcomes the known problems with this type of combination pump, namely long activation time or high current handling within the pump.

The design of the vacuum system for the joint German-British interferometric gravitational wave detector, GEO

Developments in the design of the vacuum system for the proposed gravitational wave detector, GEO, are described, together with some small scale tests. The vacuum chamber will consist of two horizontal stainless steel tubes, 1.4 m diameter and 3 km long, arranged in an L, connecting a number of experimental tank stations. By heating the tubes to 200°C in air, followed by a vacuum bake at 150°C, an outgassing rate of ∼ 10 −13 mbar l s −1 cm −2 will be achieved. Turbomolecular and non-evaporable getter pumps have been chosen to minimise pressure fluctuations and provide a hydrocarbon-free vacuum of ≤10 −8 mbar.

The U5.0 Undulator for the Advanced Light Source

The U5.0 Undulator, an 89 period, 5 cm period length, 4.6 m long insertion device has been designed, is being fabricated, and is scheduled for completion in early 1992. This undulator will be the first high brightness source, in the 50 to 1,500 eV range, for the Advanced Light Source at the Lawrence Berkeley Laboratory. A hybrid magnetic configuration using Nd–Fe–B permanent magnet material and vanadium permendur poles has been selected to achieve the field quality needed to meet performance requirements. The magnetic structure is modular with each half consisting of five assembly sections, which provide the periodic structure, and end structures, for entrance and exit correction, mounted on a steel backing beam. Each assembly section consists of 35 half-period pole assemblies bolted to a mount. The required 0.837 T effective peak field at a 1.4 cm gap has been verified with model measurements. Vertical field integral correction is accomplished with the end structures, each having an arrangement of permanent magnet rotors which will be adjusted to minimize electron beam missteering over the undulator operating field range. To reduce the effect of environmental fields, the steel backing beams are connected through parallel, low-reluctance, Ni–Fe hinges. The magnetic structure is connected through four rollernuts to the drive system that provides gap adjustment with an arrangement of roller screws, chain drives, a gear reduction unit, and a stepper motor driven by a closed loop control system. Magnetic structure and drive system support are from a 2.4 m high structure which includes a support base with four vertical supports. The vacuum chamber design is a two-piece machined and welded 5083-H321 aluminum construction of 5.1 m length. Pumping is with a combination of ion, titanium sublimation pump and nonevaporable getter pumps. Magnetic design, subsystem design, and fabrication progress are presented.

Performance Characteristics of Lumped Nonevaporable Getter(NEG)Pump.

A prototype of the lumped NEG pump (LNP) designed as a main pump of the crotches and absorbers of the SPring-8 storage ring was manufactured with 14 nonevaporable getter (NEG) modules and a cylindrical pump body made of aluminum alloy. Vacuum Performance and operating characteristics of the LNP have been tested. Initial pumping speeds of the LNP for H2, CO, N2 and CO2 were typically 3 m3/s, 1.7 m3/s, 1 m3/s and 1.3 m3/s, respectively. The experimental results were compared with the pumping speeds calculated by the Monte Carlo method. Equilibrium characteristics of the LNP in the activation period were studied to obtain basic data for the design of the auxiliary pumping system, and to set a pertinent activation schedule for the LNP. Operating characteristics such as the power consumption of the NEG modules and the temperature rise of the adjacent chambers including the aluminum alloy pump body during the NEG activation were also investigated.

Room temperature pumping characteristics for gas mixtures of a Zr–Al nonevaporable getter

The main pumping for the vacuum system of the large electron positron (LEP) collider, which has been commissioned at CERN in the Geneva area, is achieved by a linear getter pump. In distinction with the usual operating conditions of nonevaporable getter (NEG) pumps, which consist in maintaining the getter hot to continuously diffuse into the getter bulk the gases adsorbed on its surface, the LEP pump will be kept at ambient temperature and heated only intermittently. This difference has required a study on the behavior of a NEG pump under these unusual operating conditions, which result in a progressive reduction of pumping speed with increasing quantity of the gas adsorbed. It was found that the pumping speed reduction may be described in terms of a progressive saturation of the NEG surface inside the cracks and porosities which are present in the getter film thickness. The formulation developed permits one to reconstruct the pumping curves of a NEG, provided that a few basic geometrical and physical quantities are known. This description, which had been applied to individual gases in a previous paper, is extended here to the case in which mixtures of different gases are pumped.

Room‐temperature pumping characteristics of a Zr–Al nonevaporable getter for individual gases

The main pumping for the vacuum system of the Large Electron Positron (LEP) collider, at present under construction in the Geneva area, will be achieved by a linear getter pump. In contrast to the usual operating conditions of nonevaporable getter (NEG) pumps, which consist of maintaining the pump hot to continuously diffuse into the getter bulk the gases adsorbed on its surface, the LEP pump will be kept at ambient temperature and heated only intermittently. This difference has required a study on the behavior of a NEG pump under these unusual operating conditions, which result in a progressive reduction of pumping speed with increasing quantity of the gas adsorbed. It was found that the pumping speed reduction may be described in terms of a progressive saturation of the NEG surface inside the cracks and porosities which are present in the getter film thickness.

Extreme Vacua: Achievements and Expectations

Obtaining pressures between 10-12 and 10-14 Torr inside vacuum systems operating at room temperature imposes severe limitations on the choice of materials and pumps. If the proper choice is made and the proper procedures are followed, the main obstacle to achieving such low pressure results from the hydrogen outgassing of the metal walls of the vacuum system. However, at the lower end of this range and for pumping systems based on getter pumps (both titanium sublimation and non-evaporable getter pumps), methane may become the main component of the residual gas pressure.Although a large effort has been devoted to developing suitable gauges, only a few of them have been actually tested at the extreme vacuum for which they were designed. Furthermore, none of the commercially available instruments is adequate for pressures below 10-12 Torr.The basic physical phenomena which contribute to defining the vacuum condition inside a system operating in this pressure range are reviewed. Guidelines to the selection of materials and pumps are given and discussed with the help of some examples.

A Vacuum System for the Argonne 6 GeV Synchrotron Light Source

The ANL vacuum system for the 6 GeV light source storage ring features non-evaporable strip getter pumps for uniform pumping around the ring within a gas desorption antechamber, and it also features lumped getter pumping directly under and above crotch radiation absorbers that are positioned after each bending magnet. Based on experiments at ANL in 1980 and by others, the technical and economical advantages have been established for the use of the distributed NeG pumps of non-magnetic strips coated with a nonevaporable Zr Al getter matrix. The NeG strip pump lifetime approaches ten years. The antechamber improves the isolation of the gas desorption process from the main beam chamber and beam. The combination oE these vacuum techniques; the NeG strip getter pumps, the gas desorption antechambers, and the lumped ion and lumped getter pumping provide a unique and reliable system for maintaining long beam lifetime.