Digital Plasma Density Determining Device

D. J. Holly, T. W. Lovell, and J. C. Sprott
Physics Department, University of Wisconsin, Madison, Wisconsin 53706
(Received 16 Nobembver 1973; and in final form, 1 April 1974)


A device is described for measuring the time dependent, volume averaged density of a decaying plasma in a large multimode microwave cavity such as is typically used for plasma confinement studies. The technique consists of filling the cavity with microwave radiation and digitally counting the modes observed with a detector as the plasma decays. Since each mode corresponds statistically to a constant density increment, the density at a given time is proportional to the number of modes that appear as the density decays to zero. Experiments in a toroidal octopole show good agreement with density as measured by other methods.

Ref: D. J. Holly, T. W. Lovell, and  J. C. Sprott Rev. Sci. Instrum. 45, 947-949 (1974)

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