Investigation of the reliability of a 1-D fluid model for Mach probe measurements

In this paper we show how a one dimensional fluid model can be used to interpret data obtained from an inclined Mach-probe or a Gundestrup probe. We use an analytical approximation of the solution of the differential equations describing the relation between the plasma flow and the measured ion saturation currents at the probe's surface. The parameters of the approximate analytical solution are determined by comparison with the exact numerical solution of the equations. In this way we are able to measure the parallel as well as the perpendicular Mach numbers over the whole parameter range with a minimum accuracy of 90%.