Non-evaporable Getter Material Research Articles

Comparison of two vacuum system technologies for the synchrotron storage ring: case study of Iranian Light Source Facility

The current study compares two vacuum system designs for the Iranian Light Source Facility (ILSF) storage ring: conventional vacuum system design with stainless-steel vacuum chambers that are pumped by Non-Evaporable Getter (NEG) cartridges and ion pumps. In this design, all synchrotron radiation is absorbed by the local photon absorbers. In the second design, the water-cooled copper tubes that are coated with NEG materials are used as the vacuum chambers. This study will illustrate the advantages of using the NEG-coated vacuum chambers over the conventional design with the stainless-steel chambers. Since the two designs for ILSF are now completed, some of the details of this comparison might be interesting to other light sources, especially those that have plans to upgrade to a 4th generation.

Effect of Adding Al on the Phase Structure and Gettering Performance of TiZrV Non-Evaporable Getter Materials.

Titanium zirconium vanadium (TiZrV) is a widely used non-evaporable getter (NEG) material with the characteristics of a low activation temperature and a large gas absorption capacity. At present, the research on TiZrV getters mainly focuses on the thin-film state, with little research on the bulk state. In this paper, a TiZrV getter was optimized by adding Al, and the phase structure, activation properties, and gettering performance were studied. With the addition of Al, the α-Zr phase and Ti2Zr phase changed into the Ti-Zr phase and Al-Zr, Al-Ti phase. The newly generated phase promoted the diffusion of hydrogen and oxygen atoms. The activation temperature decreased significantly, as shown in the in situ XPS results. The H2 and CO gettering performance of TiZrVAl samples was promoted to 2073 cm3·s-1 and 1912.8 cm3·s-1, increased by 40.7% and 40.3%. This paper provides valuable ideas for optimizing the properties of bulk TiZrV getters.

Preliminary evaluation of NEG materials in view of CMSB replacement in HCPB TER architecture

CMSB (Cryogenic Molecular Sieve Beds) operated at 77 K is used for tritium recovery in the reference design of HCPB (Helium Cooled Pebble Bed) TER (Tritium Extraction and Removal) system. However, this technology has two main drawbacks: large consumption of liquid nitrogen and the controlling of tritium stream sent to the Tritium Plant, during the regeneration of the CMSB, in such way to avoid large variations in the gas flow rate.This paper reports on a preliminary evaluation for CMSB replacement by non-evaporable getter materials for tritium recovery. The advantages of NEG technology are the high specific pumping speed and capacity and the ability to withstand a large number of absorption/desorption cycles. In addition, NEG do not release hydrogen unless power is supplied to heat them, addressing an important safety issue related to uncontrolled release in case of power outage or subsystem failures.

Modeling of the HCPB Helium Coolant Purification System for EU-DEMO: Process Simulations of Molecular Sieves and NEG Sorbents

The Helium Cooled Pebble Bed breeding blanket of the EU-DEMO foresees continuous processing of a small fraction of the helium coolant in the coolant purification system (CPS) to counteract buildup of tritium and impurities. For this system, two different process variants are currently considered. The first is based on the conversion of all hydrogen species into water using copper oxide beds and the subsequent water adsorption over zeolite molecular sieve (ZMS) beds. The alternative process foresees the direct sorption of hydrogens onto novel ZAO® non-evaporable getter (NEG) materials. The ZMS beds and the NEG beds are operated batchwise, but alternating schemes with an absorption (operation) phase and a desorption (regeneration) phase result in a pseudocontinuous process. Transient process simulations have been developed to evaluate the performance and impact of the different variants on downstream systems in the fuel cycle. In this contribution, these process models for the preconceptual design of both variants are presented and evaluated. For the reference designs proposed for each system, they have been found to satisfy the requirements of achieving 90% efficiency. This modeling then lays the foundation for optimization of the conventional process and outlines further research demand regarding the application of NEG materials needed to progress toward the concept design of the CPS process.

Synthesis, characterization, and thermal analysis of Ti-Co, Zr-Co, Ti-Co-RE and Zr-Co-RE based non-evaporable getter materials

In this paper, we are investigating the Samarium (Sm) and Gadolinium (Gd) substituting on the sorption properties of Ti-Co, Zr-Co, Ti-Co-RE and Zr-Co-RE getter materials. Four types of non-evaporable getter materials are successfully prepared by simple solid state reaction method from 16Hr's grinding process and the activation temperature 1000 °C. The results of gas sorption properties are investigated through thermo gravimetric analysis (TG/DTG) and differential scanning calorimeter (DSC), structural process investigated by X-ray diffraction (XRD), and the morphological studies achieved by field emission scanning electron microscope (FESEM) with energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) techniques. The main purpose of this study is to show better sorption properties phase and surface properties of the addition of rare earth elements of the Samarium and Gadolinium.

Novel Non-Evaporable Getter Materials and Their Possible Use in Fusion Application for Tritium Recovery.

Non-evaporable getters (NEGs) are metallic compounds of the IV group, particularly titanium and/or zirconium-based alloys and are usually used as pumps in vacuum technologies since they are able to sorb, by chemical reactions, most of the active gas molecules, with particular efficacy towards hydrogen isotopes. This work suggests an alternative application of these materials to fusion nuclear reactors, where there is the need to recover small amount of tritium from the large helium flow rate composing the primary coolant loop. Starting from the tritium mass balance inside the primary coolant loop, the amount of coolant to be routed inside the coolant purification system (CPS) is identified. Then a feasibility study, based on the bulk getter theory, is presented by considering three different commercial alloys, named ST707, ST101 and ZAO. The results provide the mass, the area and the regeneration parameters of the three different alloys necessary to fulfill the requirements of the CPS unit. By comparing the features of the three alloys, the ZAO material appears the most promising for the proposed application because it requires the lower amount of material and a lower number of regeneration cycles.

Deposition and characterization of Pd–Ti thin film by sublimation

Pd/Ti double-layer thin film as non-evaporable getter (NEG) was deposited by sublimation, and its activation temperature was as low as 100 °C. The Pd film was deposited in situ after Ti deposition to ensure no oxidization on Ti film. The pumping speed of the coated pipe was measured by a pumping speed test system. The sticking factor was calculated by Molflow. The surface morphology was observed by a scanning electron microscope (SEM). The chemical composition of the film was measured by an energy-dispersive spectrum inbuilt with the SEM. The crystalline structure of the film was measured using grazing incidence X-ray diffraction. It was found that the pumping performance of the Pd/Ti film still remained high after 15 times of activation. The maximum pumping speed after heating at 100 °C for 24 h was 1.1 L/s cm2 and 0.49 L/s cm2 for H2 and CO, respectively. It can be concluded that the key to reducing the activation temperature of NEG materials is to enhance the oxidation resistance of the surface of NEG.

Improved pumping speeds of oxygen-free palladium/titanium nonevaporable getter coatings and suppression of outgassing by baking under oxygen

Oxygen-free palladium/titanium (Pd/Ti) is a new nonevaporable getter material with an activation temperature as low as 133 °C. Because pumping speeds of oxygen-free Pd/Ti for H2 and CO have been reported to be improved by baking under an O2 atmosphere, the authors investigated oxygen-free Pd/Ti samples heated in an ultrahigh vacuum (UHV) or under an O2 pressure of 1.3 × 10−4 Pa by x-ray photoelectron spectroscopy. The authors found that carbon contamination decreased to an extent on heating in UHV, but decreased considerably on heating in O2. Pressure-curve measurements in an oxygen-free Pd/Ti-coated chamber show that pumping speeds for H2 and CO were considerably improved after baking the chamber under an O2 pressure of 1.3 × 10−4 Pa (O2 baking) in comparison with baking in UHV. Furthermore, partial-pressure measurements suggested that O2 baking removes adsorbed carbon and hydrogen, and consequently suppresses the formation of H2, CO, H2O, and CH4. Catalytic chemical reactions on the Pd surface appear to be responsible for the removal of adsorbed carbon and hydrogen. The pumping speeds of the oxygen-free Pd/Ti-coated chamber for H2 and CO were measured by using the orifice method and were found to be improved after O2 baking. O2 baking is therefore useful for improving pumping speeds for H2 and CO and for reducing the partial pressures of H2, CO, H2O, and CH4.

In-Situ Electrical Characterization of Low Temperature Getter Thin Films Activation

Non-evaporable getter materials based on transition metal alloys (Zr, V, Co, Fe, etc…) are reactive materials able to sorb species like O, N, H or C. Integrated as thin films inside MEMS packages under vacuum, they can compete with desorption during bonding and leaks during time. Their thermo-electrical characteristics under varying atmospheres reflect the evolution of the microstructure and is dependent on the sorption properties. In this frame, 4-probes electrical resistivity measurements have been performed on different getter binary alloys under partial vacuum as a function of the temperature to investigate their activation and evolution.

Characteristics of Gas Mixture Supply/Pressure Control Using Non-Evaporable Getters in a Discharge-Type Fusion Neutron Source

The first tritium burning experiments of the discharge type fusion neutron source were conducted in January 2015, using a 93% deuterium and 7% tritium gas mixture. In order to conduct the experiment in a closed environment, a gas feed and exhaust system using non-evaporable getter material was prepared. This system was designed to minimize tritium usage and produce measurable changes in the neutron production rate on the basis of the dependence of the equilibrium pressure on getter temperature as included in the manufacturer’s data sheet. However, the present experiments revealed that the gas supply was insufficient and that the discharge duration was limited to about 2 minutes by the pressure drop during discharge.To determine the cause, verification experiments using hydrogen and deuterium gas were performed. It was found that the pressure variation with getter temperature could be mimicked by exploiting isotope effects and adjusting the hydrogen/deuterium concentration in the getter material according to the gas released into the vacuum chamber. Moreover, prolonged maintenance of a discharge was demonstrated by roughly tripling the amount of gas.The tritium concentration in the gas mixture, estimated on the basis of the present results, varied between 1.5% and 6.7% according to the assumptions used.

Ti–Zr–V non-evaporable getter films: From development to large scale production for the Large Hadron Collider

Non-evaporable getter (NEG) alloys after dissolution of their native oxide layer into the bulk are able to pump most of the gases present in ultra-high vacuum systems. The dissolution process, commonly called activation, is obtained by heating in vacuum. NEG materials can be sputter-deposited as a thin film on the inner wall of a vacuum chamber, transforming it from a source of gas into an effective pump. The most significant advance in the development of NEG films was the discovery of a very low activation temperature (180 °C for 24 h heating) in a large range of compositions of the Ti–Zr–V system. This favourable property was correlated with nanometric grain size of the film (about 3 to 5 nm). In addition to pumping, NEG films lead to reduced induced gas desorption and secondary electron yields. As a consequence, Ti–Zr–V films provide the optimum solution to most of the problems encountered in vacuum systems of modern particle accelerators for high energy physics and for synchrotron radiation facilities. In the near future the most significant benchmark for Ti–Zr–V films will be the Large Hadron Collider (LHC) presently under construction at CERN, where about 6 km of beam pipe are being coated. A dedicated magnetron sputtering facility has been built to cope with the high number of vacuum chambers (about 1200) and the tight production schedule.

Kinetics of hydrogen uptake for getter materials

This paper studies the kinetics of hydrogen absorption for a non-evaporable getter material, and presents a basic gettering model. Hydrogen uptake takes three processes in this model: molecular dissociated chemisorption on the surface, atomic penetration from the surface to the bulk, and diffusion in the body. For low hydrogen bulk concentration a lattice-gas model is adopted to describe the diffusion behaviour of hydrogen in the bulk. The exact analytical solutions are given for the pumping hydrogen by solving rate equations of these three processes simultaneously. The influences of some factors on the hydrogen absorption rate are also discussed. The theoretical calculations are in good agreement with the experiments performed with a Zr–Al (16%) getter and a Zr film on the Mo substrate.

Influence of the elemental composition and crystal structure on the vacuum properties of Ti–Zr–V nonevaporable getter films

Nonevaporable thin film getters based on the elements of the fourth and fifth columns of the periodic table were deposited by sputtering. Among the some 20 alloys studied to date, the lowest activation temperature (about 180 °C for a 24 h heating) was found in the Ti–Zr–V system with a well-defined composition range. Characterization of the activation behavior of such Ti–Zr–V films is presented. The evolution of the surface chemical composition during activation is monitored by Auger electron spectroscopy and the functional properties are evaluated by pumping speed measurements. The pumping speed characteristics are quite similar to those already measured for commercially available nonevaporable getter materials, except for the much lower saturation coverage for CO. This inconvenience, which is due to the smooth surface structure of these films, can be counteracted by increasing the roughness of the substrate.

Semiconductor on glass photocathodes for high throughput maskless electron beam lithography

Previous results obtained from negative electron affinity (NEA) photocathodes have shown high brightness (1×108 A/cm2sr at 3 kV), energy spreads as low as 50 meV at room temperature, uniform sensitivity to red and infrared light over cm2 areas, picosecond-scale switching, and low emission noise. These properties make possible a number of new electron beam tools, including a high-throughput multibeam maskless wafer exposure tool. Simulations show that up to 10 μA of current at 50 kV can be delivered to the wafer in such a system with a total spot diameter of 70 nm. The main obstacle to the use of NEA photocathodes in lithography instruments is the issue of cathode stability and lifetime. An ultrahigh system vacuum was built to activate and evaluate NEA photocathodes in a demountable system that includes areas with poorer vacuum. In this system a low quantum efficiency photocathode (<0.1%) was maintained at constant emission up to 190 nA with no discernible decay. A higher-efficiency cathode provided a brightness estimated at 2.2×107 A/cm2sr at 5 kV. Lifetime measurements on this cathode showed no measurable effect from resist exposure, and stable emission of 375 nA for 15 h, followed by a steady decay of ∼1.5%/h with no re-cesiation. Higher current results (3.75–1.3 μA) show a decay rate of ∼6%/h without re-cesiation. The use of cesium in a feedback loop was shown as an effective way to stabilize emission. Furthermore, the decay is limited to an area 2.6 mm in diameter, as the rest of the cathode is shielded by nonevaporable getter material. This result indicates that the source lifetime can be extended hundreds of times by simply moving the cathode to expose a fresh area. A moveable NEA photocathode in combination with a cesium source in a feedback loop promises to be a highly reliable, long-lifetime electron source.

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.

Nonevaporable Getters: Properties and Applications

Many advanced technologies, such as surface science, semiconductor processing and high energy physics, call for vacuum levels of the order of 10−11 mbar and lower. These pressures can not be reached without a careful choice of materials, treatments, and evacuation means for the vacuum device involved. Non-evaporable getters (NEGs) are increasingly being recognized as an interesting and powerful solution for many vacuum problems. NEGs have been used extensively in sealed-off devices such as microwave tubes, traveling wave tubes, x-ray tubes, lamps, and infrared detector dewars, in which their main role is to assure the desired vacuum level throughout the life of the sealed device. The getter material can be considered as a chemical pump which removes the active gases in the residual atmosphere of the vacuum device by forming stable chemical compounds.The choice of materials, treatments, and structures of nonevaporable getter materials is critical for the optimization of the sorption and diffusion processes which are the basis of the NEG pumping mechanism. The effectiveness of this pumping mechanism at very low pressures, and the cleanliness and simplicity of operation have made this pumping approach ideal, in combination with other pumping technologies, for reaching the extreme high vacuums today's advanced technologies require. This article will explain the mechanism of the gettering process, describing materials, treatments, and structures used in standard vacuum practice, and will review some of the most typical and interesting applications.

Behavior of sorb–ac wafer pumps in plasma machines

Vacuum pumps used in machines studying plasma physics are exposed to peculiar operating conditions. Especially the auxiliary pumps, such as cryopumps and getter pumps which are used in close proximity to the discharge or in injectors, can be exposed to very severe conditions. These pumps must exhibit very high pumping speeds and capacities, particularly for hydrogen, and must operate over a wide range of pressures. They must also be safe and reliable in use. Finally, their characteristics should not be influenced by energetic particle bombardment, radiation incidence, sputtered material on the sorbing surface, and by the presence of radioactive substances. The behavior of getter pumps based on the use of nonevaporable getter material and on a modular structure, known as sorb–ac wafer pumps, is reviewed and discussed here. The operating conditions and the behavior under radiation, particle bombardment, vacuum breakage accidents, etc. of these pumps meet most of the requirements in nuclear fusion machines and make them particularly suitable for this field of application.

A non-evaporable getter for low temperatures

New getters are described in which extremely large specific surface areas are obtained with non-evaporable getter materials. They consist of a sintered mixture of zirconium and graphite which gives an extremely porous product, but nevertheless presents excellent mechanical properties. Experimental evidence concerning the bulk gettering action and the mechanical properties is presented. The getter is mounted with an integral filamentary heater which allows activation of the porous mass. Sorption characteristics are presented for H 2, N 2 and CO, with the getters activated in diverse practical conditions. Finally, a brief comparison with existing gettering techniques is made to indicate the fields of application of the new device.

980. Influence of the pre-evacuation cycle on gas atmosphere in a Penning pump system: L Holland et al, Nuovo Cimento Suppl, 5 (1), 1967, 292–300

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.

979. Mean adsorption time of oil molecules used in vacuum techniques: G Tominaga, Nuovo Cimento Suppl, 5 (1), 1967, 274–283

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.