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 e i T / T from the edge of the confined plasma into the scrape-off layer (SOL) is produced by compiling the available i T measurements. The picture that emerges is that in the SOL, as well as in the edge, i T is systematically higher than e T (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.3

Ion temperature fluctuations in the ASDEX Upgrade scrape-off layer

“…7 was observed in L-mode plasmas in a number of limiter and divertor tokamaks ( [37] and references therein). In the divertor configuration, e i T T > in the SOL can be explained by higher parallel conductivity of electrons compared to that of less mobile ions, so that electron fluid experiences stronger cooling by parallel losses to a divertor [38].…”

A theoretical interpretation of the main scrape-off layer heat-flux width scaling for tokamak inner-wall limited plasmas

“…Since it is typically observed that > T T i e in the SOL [22], we comment on the neglect of T i in the model. The effects of finite T i are exhaustively analyzed for the IWL configuration by Mosetto et al [17], finding altogether a weak contribution to the SOL transport dynamics.…”

Finite ion temperature effects on scrape-off layer turbulence

“…While most of the experimental campaigns are based on the use of retarding field analyzer probes (see Ref. 1 and references therein for a review of measurements before 2010, and Refs. 2-6 for more recent experimental campaigns), also other techniques are employed, such as the charge-exchange recombination spectroscopy, 7 the ion sensitive probe, 8 or the pinhole probe.…”