The modification of the plasma edge and impurity production by antenna phasing during ICRF heating on JET

Abstract

During r.f. experiments on JET a strong modification of the plasma edge is generally observed. Density and temperature profiles in the scrape-off layer usually flatten and enhanced impurity and neutral influx is observed. Metallic impurity influx originating from antennae screens is also observed. This is especially true when the antennae are phased so that the excited spectrum contains a large fraction of power in the waves with k/sub ///=0-3 m-1. A radially localized enhancement of the particle diffusivity Dperpendicular to (a) across the plasma edge results. When the antennae are phased in the quadrupole configuration with the maximum power emitted at k/sub ///=7 m-1 a strong modification of the edge is not observed. The scrape-off layer profiles scale as in the ohmic discharges. Then both the light and metal impurity influxes become substantially reduced.