Ion energy measurements in the scrape-off layer of MAST using a Retarding Field Analyzer

Abstract

We present first ion energy measurements obtained in the scrape-off layer (SOL) of the MAST tokamak using a Retarding Field Analyzer (RFA). Results from two sets of experiments are reported. First, ion temperature (Ti) profiles were measured in L-mode discharges. Ti is lower than 20eV and larger than the electron temperature with a ratio in the range 1–2.6, even in beam-heated discharges. This is consistent with a relatively high degree of ion–electron thermal coupling. Second, the RFA was used to estimate the ion energy in ELMs. Two different scenarios were studied and gave very different results. In the first one, a type-I ELMy H-mode, ions with energies exceeding 500eV were found as far as 20cm away from the separatrix. More statistics would be needed to calculate Ti in ELM filaments. In the second one, featuring type-III ELMs, no ions with energy larger than 200eV were detected 10cm outside the separatrix.