MEASUREMENT OF PLASMA FLOWS IN IMS

Mach probe measurements of bias-induced ion flows were made in the Int erchangeable Module Stellarator (IMS) as a function of neutral pressur e and viscosity (which increases with minor radius) and compared to a fluid theory model. Using a probe model for an unmagnetized plasma, th e poloidal flow speed measured with a Mach probe agrees with that calc ulated from momentum balance to within 15%. The dependencies of the me asured ion flow magnitudes and decay rates on neutral pressure and vis cosity as predicted by the theory are qualitatively observed in the ex perimental measurements, clearly demonstrating the effects of both ion -neutral visions and viscosity in the damping of the bias-induced flow s. However, the measured flow direction is nearly poloidal, while the theory predicts a predominantly Pfirsch-Schluter-like toroidal flow. A lso, the two-dimensional variation at a constant toroidal angle of the parallel electron current was measured in an unbiased plasma. The mea sured profiles demonstrate the dependence of the current on both the r adial pressure gradient and the cosine of the poloidal angle, as predi cted by theory.