A comparison of mid-plane scrape-off-layer measurements with model predictions in MAST and the calculation of cross-field transport coefficients

Abstract

The outboard mid-plane values of electron density (ne) and temperature (Te) in the scrape-off-layer (SOL) of MAST are derived from target Langmuir probe measurements using OSM2-EIRENE and also using a simple two-point model. The values are compared with mid-plane measurements of ne and Te from a reciprocating probe and a Thomson scattering system for Ohmic, L- and H-modes single-null divertor (SND) discharges. The cross-field heat (χ⊥) diffusion coefficient at the low field side of SND discharges is derived both using the OSM2-EIRENE model and a two-point model coupled with a simple theory. The results are found to be similar within the errors. Typically χ⊥ values are found to lie in the range 0.5–2.0 m2 s−1 for L-mode and 0.1–0.5 m2 s−1 for H-mode. A comparison is made of the transport coefficients derived at the low and high field sides for a set of connected double-null discharges. These results are used to make preliminary observations of the effect of magnetic fields on SOL transport in MAST.