Probe method for measuring the Mach number and the flow vector in edge plasma

A planar Mach probe to measure the Mach number and the flow vector with respect to the magnetic field in the edge plasma of e.g. a tokamak is being proposed. The probe is constructed as a double probe and the saturation ion current is measured as function of the angle of rotation of the probe surface normal with respect to the magnetic field. The saturation current as function of the angle is calculated by taking a drifted Maxwellian distribution for ions and an effective size of the probe depending on the angle. From the ratio of the saturation currents for plus and minus biases respectively and from the envelope of the saturation current with respect to the rotation angle, the Mach number and the how vector can be determined.