Measurement of supersonic plasma flow using Mach probe under grid bias

Supersonic flow plasma is one of the most important plasma flow for understanding of edge plasma and deduction of supernova. In experiment, Mach number [M$_{\mathrm{0}} \quad =$ v$_{\mathrm{d}}$ / (T$_{\mathrm{e}}$/m$_{\mathrm{i}})^{\mathrm{1/2}}$] was measured by a Mach probe, which composed of two electric probes is separated by an insulator and plasma chamber is the following the specification: length $=$ 64 cm, diameter $=$ 32 cm, plasma is filament DC discharge source and the following conditions: 5 × 10$^{\mathrm{8}}$ \textless n$_{\mathrm{e\thinspace }}$[cm$^{\mathrm{-3}}$] \textless 10$^{\mathrm{9}}$, 1 \textless T$_{\mathrm{e}}$[eV] \textless 4 using Langmuir planar probe, Bulk M$_{\mathrm{0}}$ \textasciitilde 0.06 at working pressure \textasciitilde 10$^{\mathrm{-4}}$ Torr and 5 × 10$^{\mathrm{-4}}$ Torr with Kr gas with bias $=$ 80 V and discharge current $=$ 1 A, negative grid bias $=$ -100 V for ions acceleration. As the experiment result, maximum M$_{\mathrm{0}}$ was about 2.3 near grid.