Alternating Current Diagnostic Study of Diffusion in a Highly Ionized Plasma in a Magnetic Field

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Abstract
A new ac diagnostic technique has been used to study the radial diffusion of a highly ionized hollow cathode discharge plasma in a magnetic field. The method involves generating very low-frequency density waves in one region of the plasma and observing the diffusion of these waves through the remaining plasma. The spatial variations of phase and amplitude of the density modulation were measured with a Langmuir probe and compared with theoretical predictions corresponding to two possible diffusion mechanisms: Bohm and collisional-ambipolar. The diffusion coefficient entered as a variable parameter in each theory and was adjusted for best agreement with data in each case. Best agreement was obtained with the collisional-ambipolar theory using approximately the value of diffusion coefficient predicted for that diffusion mechanism for the plasma used.

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