BIASED LIMITER EXPERIMENTS ON TEXT

Experiments using an electrically biased limiter have been performed on the Texas Experiment Tokamak (TEXT). A small movable limiter is inserted past the main poloidal ring limiter (which is electrically connected to the vacuum vessel) and biased at V//L//i//m with respect to it. The floating potential, plasma potential and shear layer position can be controlled. With vertical V//L//i//m vertical greater than equivalent to 50 V the plasma density increases. For V//L//i//m less than 0 this is primarily a response to an increased particle confinement time, i. e. a decreased outward particle flux at the plasma edge. Intrinsic impurity line behavior is consistent with a reduction of the outward flux at the edge, while impurity laser ablation demonstrates no transport changes in the plasma interior. With V//L//i//m greater than 0 the results obtained are inconclusive. Variation of V//L//i//m changes the electrostatic turbulence which may explain the observed total flux changes.