Investigation of Mach probe geometry effects in weakly magnetized plasmas

Probe geometry dependence of Mach probe diagnostics in weakly magnetized plasmas has been investigated. In order to obtain sufficiently saturated ion currents, and also to experimentally obtain the angular sensitivity of differently shaped probes, the effect of superthermal electrons was measured. When using the theoretical expressions of angular distribution of the ion current as fitting functions, estimated Mach numbers largely depend on the geometry of the probe. However, by taking the ratio of upstream to downstream ion currents, the effect of magnetic field can be eliminated. Furthermore, considering the broadening of the ion collection angles, the deduced Mach numbers show good agreement regardless of the probes geometry, and do not contradict the spectroscopic results.