Boundary conditions for cryopumping in fusion machines of the Tokamak type

Due to the operating conditions of fusion machines of the Tokamak type special requirements must be met by the cryopumps. The gases to be pumped are at first H2 and D2, later also T2 and He. Besides the general aspects of cryopumping at temperatures below 4.2 K the physical properties of the condensates and their influences on the pumping process are discussed including the possibilities for cryopumping He. Furthermore the correlation between the plasma experiments and the operation of the cryopumps as well as the requirements regarding the refrigeration facilities are described.