Development of cryosorption panels for plasma exhaust cryopumping

Abstract

In large tokamaks the pumping speed required for the plasma exhaust pumping system can be obtained by means of cryopumps during the plasma burn and dwell modes of operation. The cryosorption panels presently available do not meet the special requirements (radioactive irradiation, tritium, high number of cylces, dust, impurities, etc.) specified for application in tokamaks of the next generation like Next European Torus (NET) or International Thermonuclear Experimental Reactor (ITER). Within the framework of the European Fusion Technology Programme, cryosorption panels which can be operated under tokamak conditions are being developed by KfK (Karlsruhe Nuclear Research Centre). The KfK development programme for cryosorption panels started in 1987. It included the development of an inorganic bonding technology of sorbent materials to metal surfaces. In thermal cycling tests with small scale specimens (50 mm diam.) the bonding resistance against thermal stresses is tested. In screening cryosorption tests at 4.2 K, the pumping speed and cryosorption capacity for helium are investigated. Cryopumping tests on technical scale are carried out with a view to select the best panels. Pumping tests using cryosorption panels of 430 mm in diameter started in 1990. In the first test series a panel was used with activated charcoal as sorbent, bonded to the copper substrate by reactive braze. The pumping behaviour for helium and NET/ITER relevant exhaust mixtures has been demonstrated. In the present paper the status of the project is described and the results achieved are discussed.