Calibrations of Fast Ion Flux Measurement Using a Hybrid Directional Probe

Abstract

A hybrid directional probe method both “thermal and Langmuir probe” was applied for fast ion measurements in the compact helical system. In order to obtain absolute values of fast ion density and power density, a calibration of the probe was performed using neutral hydrogen beam and a mixture beam of hydrogen and proton, of which beam current and energy were controlled. The conversion factor from temperature increase of the probe head to local power density and secondary electron emission yield was obtained. The density of fast ions was obtained by directional thermal probe (DTP) method inside the last closed flux surface, and the density ratio was n_FastIon/n_BulkPlasma = 2.7 × 10^-3 at r/a = 0.9. The observation of the directional Langmuir probe (DLP) method is consistent with the DTP results.