The scrape-off layer in a finite-aspect-ratio torus: the influence of limiter position

摘要: The effect on the scrape-off layer (SOL) of changing position a tokamak limiter from low field side (LFS) to high (HFS) plasma is considered. Conservation magnetic flux in SOL requires that area, A||, for flow particles and energy parallel field, be smaller HFS. this reduction A|| has that, when HFS, as compared with LFS, then characteristic thickness increased particle densities are higher. Such increases described. They were observed an experiment JET which was limited first LFS then, during same discharge, magnitude larger than expected, line integrated density SOL, nλn, having average increase by factor 5.8 ± 1.1 7 at respective limiter. Moreover, there power flow, λp, 2.5 0.4 average, corresponding 3.0 n λn can substantially improve screening recycled wall pumping, although not strongly experiments described, helium avoid these effects. large λp measured useful spreading over area Evidence presented suggests either enhancement above expectations due Mach number sheath HFS or fundamental problems modelling procedure usually used SOL. Related discussed