Effect of pressure on the radiation induced electrical conductivity of NBI insulator gases

A study of the effect of pressure on the radiation induced electrical conductivity (RIC) of candidate international thermonuclear experimental reactor (ITER) neutral beam injectors (NBI) insulation gases has been carried out. Large volume, pressure and voltage values similar to those for the ITER system are not readily achievable experimentally. To overcome this problem different experiments have been performed in a Van de Graaff electron accelerator at lower values and the results compared with a theoretical model. Excellent agreement is found between theoretical and experimental results allowing extrapolation to the higher voltage, gas volume and particularly higher gas pressure required in the ITER design. The results show that the use of high gas pressure to increase the voltage breakdown threshold and reduce size may also result in enhanced leakage current losses.