THE OPERATION OF A LANGMUIR MACH PROBE IN TOKAMAK-DE-VARENNES

A movable Langmuir/Mach probe apparatus has been successfully operated in the Tokamak de Varennes. Comprised of three probe elements, a tip probe acting as a standard Langmuir probe and two side probes acting as a Mach probe, this apparatus has been used to acquire simultaneous probe characteristics in the SOL of the tokamak. Densities and Mach numbers computed from four different probe models have been compared. The densities calculated from the various models are similar in magnitude and compare favorably with the extrapolated density from the interior of the plasma. However, when the same models are used to compute the Mach numbers, they vary from subsonic to supersonic for the same set of measurements. Preliminary results in a separate experiment which measures the plasma flow indicate that the Hutchinson model is in better agreement than the other models. Finally, the preliminary results of flow measurements in the TdeV indicate the presence of an appreciable poloidal velocity near the last closed flux surface.