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

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 (T-i) profiles were measured in L-mode discharges. T-i is lower than 20 eV 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 500 eV were found as far as 20 cm away from the separatrix. More statistics would be needed to calculate T-i in ELM filaments. In the second one, featuring type-III ELMs, no ions with energy larger than 200 eV were detected 10 cm outside the separatrix. (C) 2010 Elsevier B.V. All rights reserved.