Experimental test of instability enhanced collisional friction for determining ion loss in two ion species plasmas
- Department of Engineering Physics, University of Wisconsin, Madison, Madison, Wisconsin 53706 (United States)
- Department of Physics, University of San Diego, San Diego, California 92110 (United States)
Recent experiments have shown that ions in weakly collisional plasmas containing two ion species of comparable densities approximately reach a common velocity at the sheath edge equal to the bulk plasma ion sound velocity. A recent theory [S. D. Baalrud, C. C. Hegna, and J. D. Callen, Phys. Rev. Lett. 103, 205002 (2009)] suggests that this is a consequence of collisional friction between the two ion species enhanced by the two stream instability. The theory finds that the difference in velocities at the sheath edge depends on the relative concentrations of the two ions. The difference in velocities is small, with both species approaching to the bulk sound velocity, when the concentrations are comparable, and is large, with each species reaching its own Bohm velocity, when the relative concentration differences are large. To test these findings, drift velocities of Ar and Xe ions were measured with laser-induced fluorescence in Ar-Xe and He-Xe plasmas and combined with ion acoustic wave and plasma potential data. In addition, electron temperature was varied by a Maxwell demon [K. R. MacKenzie et al., App. Phys. Lett. 18, 529 (1971)]. The predictions were found to be in excellent agreement with the experimental data. The generalized Bohm criterion in two ion species plasmas is also verified in a wider variety of relative ion concentrations.
- OSTI ID:
- 21537914
- Journal Information:
- Physics of Plasmas, Vol. 18, Issue 5; Other Information: DOI: 10.1063/1.3562574; (c) 2011 American Institute of Physics; ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BOHM CRITERION
COLLISIONAL PLASMA
DRIFT INSTABILITY
ELECTRON TEMPERATURE
FRICTION
ION ACOUSTIC WAVES
PLASMA POTENTIAL
PLASMA SHEATH
TWO-STREAM INSTABILITY
VELOCITY
ELECTRIC POTENTIAL
INSTABILITY
ION WAVES
PLASMA
PLASMA INSTABILITY
PLASMA MICROINSTABILITIES
PLASMA WAVES