Local scrape-off layer control using biased electrodes in NSTX

Abstract

An experiment was designed to test the theory that biased electrodes can affect the local scrape-off layer (SOL) width by creating a strong radial ExB drift [Cohen, R.H. and Ryutov, D.D, Nucl. Fusion 37, 621 (1997)]. These electrodes were located near the outer midplane in the SOL of the National Spherical Torus Experiment (NSTX). The electrodes were biased at up to �100 Volts, and the radial profile of the plasma between them was measured by an array of Langmuir probes. The biasing caused large changes in the local SOL profiles at least qualitatively consistent with this theory