Livio Rosai

A nonevaporable low temperature activatable getter material

Nonevaporable getters have been widely used for many years in sealed vacuum or controlled atmosphere devices. They are also finding applications in other fields, where specific characteristics are required and tailor‐made getters are requested, in some cases sacrificing speed in favor of lower activation temperatures, or lower operating temperature, while still maintaining an adequate sorption capacity. With these objectives, a decade long research project was undertaken which involved investigation of Zr–V–Fe alloys. The physico‐chemical properties and the gettering characteristics (speed and capacity) of this family of alloys for some main gases usually present in vacuum devices (H2, CO, N2) have therefore been studied in a range of activation temperatures of less than about 700°C. The equilibrium pressure of H2 on these materials has also been studied as a function of concentration and temperature in a range of pressures less than ∠10 Pa. The results obtained, showing the efficiency of this type of all...

Gettering in cryogenic applications

Metallic cryogenic Dewars and pipes, used for storage and transportation of cold fluids such as liquid N2 or He, usually have a vacuum jacket as a thermal insulator. In this case, vacuum has to be maintained in a range of 10−1 Pa or lower. Nonevaporable getters are often used for this purpose. They are particularly useful for sorbing H2 which is released by the warmer walls or by the multilayer insulation; H2 is neither cryocondensed by the cold surfaces nor sorbed by the molecular sieves which may be used to physisorb other gaseous species. The working temperature of the getters may range from room temperature down to the cryogenic fluid temperature. The getter material here considered, and which appears to be adequate for these applications, is the Zr–V–Fe nonevaporable getter alloy. Its sorption characteristics (particularly for H2) are studied both at room temperature and in a cryogenic fluid environment. The behavior of a gettered Dewar jacket is finally studied and discussed.

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 a...