MEASUREMENT OF ION FLOWS USING AN UNMAGNETIZED MACH PROBE IN THE INTERCHANGEABLE MODULE STELLARATOR

A Mach probe is used to measure poloidal and toroidal flows induced by a biased electrode in IMS. Mach probe theories are reviewed and class ified as either magnetized or unmagnetized. A simple geometric model o f the IMS Mach probe shows that the variation of the effective probe a rea as a function of the probe orientation with respect to the magneti c field is 20%-25%, predicting the probe to be only slightly magnetize d. Measurements of the variation in the total ion saturation current c ollected by the probe, as the angle with respect to the magnetic field is varied, demonstrate this level of magnetization only at low neutra l pressure at large minor radius, while in other cases the variation i n the total collected current is negligible. Based on this result an u nmagnetized model [M. Hudis and L. M. Lidsky, J. Appl. Phys. 41, 5011 (1970)] is chosen to analyze the IMS Mach probe data. Comparison of Ma ch probe poloidal flow measurements as a function of minor radius to c alculations of the ExB drift velocity and the ion diamagnetic drift ve locity from radial profiles of floating potential and ion saturation c urrent, respectively, shows agreement to within 15%.