Transverse cylindrical probe in plasma diagnostics

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Abstract
A cylindrical Langmuir probe with its axis positioned transversely to the plasma flow is considered theoretically and experimentally. Together with results on electron temperature and density obtained from a complementary cylindrical probe placed parallel to the flow, the transverse probe is shown to be capable of yielding data on ion Mach number (and therefore flow velocity) at a `point'. Such a probe system is therefore useful in determining the structures of plasma shocks. Two theories were considered for the transverse cylinder: (a) when the ions are collected via an absorption surface surrounding the cylinder; and (b) when the ions are collected by the orbit-limited motion mode. Theoretical comparison with experimental data were made on the basis of the ratio of the ion current collected by the transverse cylinder to the ion current collected by a parallel cylinder of the same radius and surface area, as a function of the ion Mach number. For the first theory it is shown that agreement with experimental data is better than with previous theories.