Ion collection by cylindrical Langmuir probes in a strong axial magnetic field

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Abstract
Cylindrical Langmuir probes were used to obtain information from a potassium plasma generated in a single-ended Q-machine. The results showed the variation of probe current ip with magnetic field strength B and were compared with the predictions of a collisionless theory. The best agreement was obtained at low plasma densities (similar 1014 m−3) when utilizing a sheath thickness which was dependent upon the dimensionless parameters ξ=rp/λp and η= /kT. Poorer agreement was observed in the density region above similar 1016 m−3 and was attributed to the collisionless assumption. The effects of variation in probe bias and probe size were in keeping with the theoretical predictions. Calculation of the plasma density was obtained by an iterative method and compared favourably with predictions from Laframboise's results.