LOW Z IMPURITY ION EXTRACTION FROM TOKAMAK FUSION TEST REACTOR ION SOURCES

Tokamak Fusion Test Reactor (TFTR) deuterium neutral beams have been o perated unintentionally with significant quantities of extracted water ions. Water has been observed with an optical multichannel analyzer. These leaks were thermally induced with the contamination level increa sing linearly with pulse length. Up to 6% of the beam current was attr ibuted to water ions, corresponding to an instantaneous value of 12% a t the end of a 1.5 s pulse. A similar contamination is observed during initial operation of ion sources exposed to air. Operation of new ion sources typically produces a contamination level of approximately 2%, with cleanup to undetectable levels in 50-100 beam pulses. Approximat ely 90% of the water extracted from ion sources with water leaks was d euterated, implying that there is the potential for tritiated water pr oduction during TFTR's forthcoming DT operation. It is concluded that isotope exchange in the plasma generator takes place rapidly, most lik ely as the result of surface catalysis. The primary concern is with O implanted into beam absorbers recombining with tritium, and the subseq uent retention of T2O on cryopanels.