Studies of plasma potential measurements using an ion-sensistive probe

Abstract

The plasma potential of the scrape-off-layer (SOL) in the tokamak is a key indicator of the erosion rate of the plasma facing component (PFC) material. The Alcator C-Mod SOL plasma potential is currently measured by emissive probes, which is an established potential diagnostic, yet the probes are fragile and short-lived. The ion-sensitive probe (ISP) is a possible sturdier replacement for the emissive probe. Plasma potentials in the Dionisos plasma chamber (DPC) are compared between the two probe types. Preliminary results show the DPC electron density in helicon mode was found to imitate that of the C-Mod plasma SOL. The ISP plasma potential followed the same trend as the emissive probe plasma potential with RF power level, and the two potentials were always within the error of one another. These results indicated the ISP appears to be appropriate for use in C-Mod.