Measurements of ion energies in the tokamak plasma boundary

Abstract Measurements of ion energies in the boundary of tokamak plasmas in L-mode discharges and during ELMs are reviewed. A profile of the ion-to-electron temperature ratio T i / T e from the edge of the confined plasma into the scrape-off layer (SOL) is produced by compiling the available T i measurements. The picture that emerges is that in the SOL, as well as in the edge, T i is systematically higher than T e (ratios up to 10 just outside the last closed flux surface) for most plasma parameter regimes. Far SOL ELM ion energies measured in JET, and more recently in MAST and AUG, agree with the models of the ELM transients, providing strong evidence that ELM ions can reach the first wall with significant fraction of the pedestal energies.