ELECTRIC-FIELD AND RADIAL TRANSPORT DURING ICRF HEATING IN THE EDGE PLASMA OF JET

The plasma boundary in front of and outside the JET ICRF antenna Faraday screen has been studied using Langmuir probes. Plasma densities of nc ∼ 1015-1016 m-3 and electron temperatures Tc ∼ 20-80 eV have been measured at the Faraday screen. Both nc and Tc scale almost linearly with total input power (PRF up to 12 MW). DC electric fields up to 20 V/cm, with a large poloidal component perpendicular to the magnetic field lines were generated during ICRF heating. The total electric field intensity depends on the minority gas (H or 3He) and is also linearly dependent on the applied RF power. Spatially resolved measurements of the plasma space potential up to 50-100 V at the limiter flux surface were measured. The relevance of these fields to the transport in the scrape off layer (SOL), to the local particle balance at the boundary and to the impurity production during RF heating is discussed. © 1990.