Behavior of sorb–ac wafer pumps in plasma machines

Abstract

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.