Radiation enhanced dielectric breakdown in insulating gases for NBI systems

Abstract

During the operation of future machines such as ITER, insulating gases in the NBI systems will be subjected to a radiation field of the order of 1 Gy/s and hence the electric field threshold for dielectric breakdown could be modified. Radiation enhanced dielectric breakdown has been studied for N 2, CO 2, N 2/CO 2 mixture, SF 6, and dry air at atmospheric pressure and 20 °C. Dry air, N 2, CO 2, and N 2/CO 2 mixture all exhibit moderate radiation enhanced breakdown, with a reduction in the limiting voltage between 5 and 18% at 20 Gy/s. In contrast SF 6 does not. Following breakdown N 2 and CO 2 show no quenching of the breakdown current until the applied voltage is reduced to almost zero. Both dry air and SF 6 are good in terms of quenching the breakdown.