Radiation enhanced dielectric breakdown in insulating gases for NBI systems

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 N2, CO2, N2/CO2 mixture, SF6, and dry air at atmospheric pressure and 20 °C. Dry air, N2, CO2, and N2/CO2 mixture all exhibit moderate radiation enhanced breakdown, with a reduction in the limiting voltage between 5 and 18% at 20 Gy/s. In contrast SF6 does not. Following breakdown N2 and CO2 show no quenching of the breakdown current until the applied voltage is reduced to almost zero. Both dry air and SF6 are good in terms of quenching the breakdown.