PLASMA SHEATH TRANSMISSION FACTORS FOR TOKAMAK EDGE PLASMAS
Simple analytic relations are derived for the floating potential of a solid object in contact with a magnetized plasma as a function of the electron - ion mass ratio, the electron - ion temperature ratio, and the secondary electron emission coefficient. Simple analytic relations are also obtained for the sheath transmission factors, i.e., the particle and energy fluxes to floating and non-floating surfaces. These analytic formulations, derived from a fluid model treatment of ion flow, are found to give results in close agreement with results derived from more complex analysis based on kinetic theory and numerical models. Tokamak scrape-off plasmas are often characterized by ion distributions which have finite drift velocities at the point where the ions enter the scrape-off plasma from the main plasma (via cross-field diffusion). The Bohm criterion governing the drift velocity of ions as they enter the electrostatic sheath in front of a limiter, divertor plate, or probe is generalized for this case.
Bibliographic Reference: PHYS. FLUIDS, VOL. 27 (1984), NO. 3, PP. 682-690.
Record Number: 1989123050100 / Last updated on: 1987-01-01
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