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.