The measurement of ion flow velocity by mach probes in unmagnetized plasmas

Abstract

Summary form only given. The measurement of ion flow in unmagnetized plasmas is performed using two Mach probes, one is a planar Mach probe and the other is spherical. The planar Mach probe consists of two single sided planar Langmuir probes back to back with an insulator between them. The spherical Mach probe, which was inspired by Hutchinson's numerical calculation, consists of a conducting sphere that has two conducting probe tips, insulated from the sphere and mounted at /spl theta/=0/spl deg/ and 180/spl deg/ with respect to the flow direction. The experiments are performed in a double-plasma device for ion flow velocity v/sub f/ up to 4.5 c/sub s/, where c/sub s/ is the sound speed, and along a presheath in a multi-dipole DC plasma for v/sub f/ < 1.0 c/sub s/ with Argon pressure ranging from 0.1 to 1 mTorr and plasma density range of 10/sup 7//spl sim/10/sup 10/ cm/sup -3/. The laboratory plasma in the, presheath was limited to T/sub i/, <0.1 T/sub e/ and v/sub f//spl les/1.0 c/sub s/. The measured super-sonic ion flow velocities are compared to the velocity from ion energy using an ion energy analyzer and single sided probes.