Edge Ion Temperature Measurement in the STOR-M Tokamak

Abstract

A newly developed bidirectional Retarding Field Energy Analyzer, RFEA, which measures ion temperatures from both sides (downstream and upstream), was commissioned in the STOR-M tokamak. Its entrance slit width follows one of the design criteria, < 2 lambda_{De}. The dimension of the RFEA is small enough to avoid creating a shadow effect. The probe is the replacement of previous RFEA which measures ion temperature, T_i, from one side only. An external cable used as an antenna parallel to the cables, connected to the collector, is used to suppress noise picked up by the cable. A similar technique was used in the previous RFEA. By operating the probe in standard ramping mode, T_i in the scrape-off layer (SOL) region between 15.5cm and 12cm from the chamber center is measured (minor radius). The probe performs T_i measurement campaign twice with different entrance slits. The entrance slit 1 provides higher collector current than the entrance slit 2, but the entrance slit 1 on the downstream side did not survive during the fi rst T_i campaign. T_i measured by the entrance slit 2 in the SOL region of the STOR-M is between 19eV and 34eV. The probe operation is validated by T_e values simultaneously measured by the Triple probe. T_i/T_e is between 1.8 and 2.8 in the STOR-M SOL. RFEA in DC mode operation demands higher ion current to estimate T_i fluctuation. The 2011 Ti campaign shows that the direction of magnetic fi eld largely affects the current RFEA operation both in conventional ramping mode and in DC mode.