Measurement of H energy and flux by H→D isotope exchange in JFT-2M scrape-off layer

Abstract

The energy and flux of H particles in the scrape-off layer (SOL) of JFT-2M were determined in H plasma discharges by measuring the retained amount of H incident on C edge probes as a function of number of discharges. The uncertainty in measuring H retention was avoided by using C samples implanted beforehand with D to a saturation level. The decrease in retained D was more easily measurable and was taken as the H retention. The validity of such replacement was examined with the local mixing model (LMM). By using a proper geometrical arrangement for probe samples the H + ions were separated from H 0 neutrals. At a specified halfway position in the SOL, about 30% of the total H density is found to consist of H + with a flux of (1.4±0.5)×10 16 H/cm 2 s while the remaining density (70%) is made up of H 0 having a flux of (3.3±1.2)×10 16 H/cm 2 s. In both cases, the particle energy is 30±9 eV.