Structure of the plasma and energy balance near the limiter in the L-2 stellarator

Abstract

The results of a study of the properties of the edge plasma in the L-2 stellator are reported. The edge plasma can be divided into three radial regions: a low density region between the wall and the separatrix ( n e ≤ 1 × 10 9 cm −3), a high gradient region near the separatrix and a region inside the separatrix zone with density ~ n e ≤ 1 × 10 12 cm −3. Edge turbulence is found to be sensitive to the mode of plasma heating. Edge plasma data from the stellarator is compared with that from the TV-1 tokamak. An energy balance in the near limiter zone of the stellarator is analysed from experimental measurements of the radial heat flux profiles and also from numerical simulations based on a theoretical model. It is shown that the experimentally measured limiter efficiency is well described theoretically.