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During the final deuterium-tritium phases of the TFTR and JET tokamaks, half of the neutral injectors will be used to produce tritium neutral beams to maintain an equal mix of deuterium and tritium in the core plasma; such requirements may also occur in future devices. This will require that the voltage hold-off capabilities of the high voltage insulators in the accelerators be unimpaired by any charge buildups associated with the beta decay of adsorbed layers. Tests measured the drain currents under high voltage of TFTR and JET accelerator insulators while they were successively exposed to vacuum, deuterium and tritium. There did not appear to be any substantial reduction in hold-off capability with tritium, although at some voltages there was a small increase in the leakage current. The breakdown properties of a plastic tubing filled with deuterium and then tritium were compared at varying pressures, since such tubing has been considered as a high voltage break in the gas feed system for TFTR, and the presence of large numbers of electron-ion pairs might lead to enhanced Paschen breakdown. No significant differences were found in the behaviour for the geometry used.

Additional information

Authors: GRISHAM L R ET AL., JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(90)07 EN (1990) 14pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199010997 / Last updated on: 1994-12-01
Original language: en
Available languages: en
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