Helium partial pressure measurements using a Penning gauge. A new approach

Future magnetic-confinement devices which produce significant power by the fusion of D-T nuclei will require an adequate removal rate of helium ash from the plasma core, in order to maintain core purity and the level of power production. Hence, the role of the divertor in removing helium is of crucial importance. At JET, several divertor configurations have been studied to characterise their efficacy at this task, under various operating conditions. The partial pressures of the deuterium and helium in the sub-divertor volume are measured using a Penning gauge, which is a well-established technique. In this paper, a new approach to the measurement is described, which is particularly useful for plasmas with high and varying concentrations of helium