Measurement of plasma flows using Mach probe arrays

Abstract

A rectangular array of three-dimensional Mach probes is constructed and installed in the plasma vessel of the Versatile Toroidal Facility (VTF) at MIT in order to measure ion flow velocity on the cross section of the VTF. The probes are tested using well-characterized toroidal plasma 'blobs' in order to determine the array's functionality and applicability to measuring ion flow during reconnection events in the VTF. The Mach probe is used to infer the radial speed of the blobs, and the blob speeds are measured independently by a Langmuir probe array. Using the blob velocity dataset from the Langmuir array as a reference with which to compare the Mach probe data, the theory of unmagnetized Mach probes is be tested. Additionally, the inverse proportionality between blob speed and neutral pressure shown to exist in a previous study of blobs in the VTF is confirmed by Mach probe data. Finally, data from the array show that the blobs are rotating clockwise with Mach numbers of between 0.1 and 0.2, although the mechanism driving this rotation is unknown.