Use of Mach probes and Langmuir probes in a drifting unmagnetized nonuniform plasma

Conference · Thu Jul 01 04:00:00 EDT 1999

OSTI ID:20067591

Oksuz, L; Hershkowitz, N

Although Mach probes have been used to measure the ion drift velocities in fusion plasma applications, their operation in unmagnetized plasma is less well understood. The effects of nonuniform drifting plasma on Langmuir probes and Mach probes have been investigated in a multi-dipole plasma. The Mach probe data were collected for different probe sizes and for different noncollecting part biases. Controlling the voltage of the noncollecting part of the mach probe makes the collecting part of the I-V traces less noisy. While different biases applied to the noncollecting part perturbed the collected data, the current ratios didn't change if the applied bias voltage was comparable to the plasma potential Using Mach probes, diameters 0.125 inches and 0.375 inches, (smaller than the ion collision length approximately 3 cm at 1mTorr) didn't change the current ratios. The total current from both sides of the mach probe was equal to the current collected by a two sided Langmuir probe. The calculated plasma potential from the Langmuir probe was found to be the average of the plasma potentials calculated from each side of the mach probe. mach probe theory was found to be consistent with the experimental results. using this Mach probe theory, the ion drift velocity profile was obtained in nonuniform drifting plasma and the plasma characteristics were determined. The density gradient, electric field and collision play a role in determining the plasma drift. The ions start to drift at the center of the plasma and at the presheath entrance they drift at 5--6% of the ion sound velocity. Up to the presheath, ambipolar diffusion plays a role. The Mach proves data and fluid theories were compared. Comparison shows ionization is important in the presheath. With the fluid theory one can also use a Langmuir probe to find the drift velocity profile at the presheath.

• Research Organization: Univ. of Wisconsin, Madison, WI (US)
• Sponsoring Organization: US Department of Energy
• DOE Contract Number: FG02-97ER54437
• OSTI ID: 20067591
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AMBIPOLAR DIFFUSION
INHOMOGENEOUS PLASMA
ION DRIFT
LANGMUIR PROBE
PLASMA DIAGNOSTICS
PLASMA DRIFT
PLASMA SHEATH