Abstract
Direct measurements of velocity-space transport coefficients, which may be interpreted as the Fokker-Planck coefficients, in the direction of the confining magnetic field are reported. The measurements were made using the techniques of laser-induced fluorescence and optical tagging, which allow ions to be followed in phase space. The results show that in a plasma with nearly only thermal fluctuations the data agree well with test particle calculations made by N. Rostoker for classical collisional processes. In the presence of larger-amplitude drift-wave fluctuations there is a pronounced enhancement of the velocity diffusion coefficient at a velocity less than the thermal speed.
Highlights
which may be interpreted as the FokkerPlanck coeScients
The measurements were made using the techniques of laser-induced fluorescence
which allow ions to be followed in phase space
Summary
The measurements were made using the techniques of laser-induced fluorescence and optical tagging, which allow ions to be followed in phase space. To take the tagging measurements an initial velocity scan of the plasma ions was made with the tagging laser. This yielded a calibrating scan that allowed us to determine the zero velocity point in the plasma reference frame (the plasma drifts toward the cold collector at nearly twice the thermal speed). 24 FEBRUARY 1992 required for the tagged particles to equilibrate with the background In principle this should yield enough information to enable the calculation of a velocity-space diffusion coefficient if one knows the initial frequency width of the laser line.
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