Tr anspor t and fluctuations dur ing electr ode biasing on TJ -II

Asociacion Euratom/Ciemat, 28040 Madrid, Spain 1. Introduction The influence of limiter biasing on plasma confinement, turbulence and plasma flows have been previously investigated in detail on the TJ-II stellarator [1]. Experimental results showed that it is possible to modify global confinement and edge plasma parameters with both positive and negative biasing and showed evidence of electric field induced improved confinement via multiple mechanisms. Electrode biasing is expected to introduce more substantial changes in energy and particle confinement than limiter biasing as it has the advantage of forcing an electric field in the edge plasma. In this contribution we report on the results of edge polarization experiments carried out in TJ-II using an electrode. The effect of bias at different densities is studied, particularly in what concerns their effects on the edge plasma parameters and particle confinement. 2. Experimental set-up Experiments were carried out in ECRH plasmas (P