POLOIDAL SOL ASYMMETRIES AND TOROIDAL FLOW IN DITE

In this paper an experimental investigation of asymmetries in the DITE plasma boundary will be presented for a limiter configuration consisting of a pumped limiter centred on the outside midplane and an inner bumper limiter displaced approximately 70-degrees toroidally. A number of experiments have been performed in which the poloidal variation of the edge T(e), n(e) and j(sat) has been monitored as a function, principally, of the direction of plasma current and toroidal magnetic field. Poloidal asymmetries in particle flux are observed with the measured flux increasing towards the outside midplane. The poloidal variation of T(e) is less marked. Considerable e-i side asymmetries are evident in the particle flux which, when interpreted as indicative of net plasma flow, give poloidally varying Mach numbers and flow directions dependent on the toroidal magnetic field direction and line-averaged central density. The persistence of the observed asymmetries when the magnetic field and plasma current directions are reversed show the effect to be related to plasma properties and not simply a consequence of varying connection lengths.