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Signatures of ring currents in a magnetic mirror plasma experiment
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Date
2019-12-19
Authors
McCarthy, Patrick J.
Knott, Sean
Journal Title
Journal ISSN
Volume Title
Publisher
IOP Publishing
Published Version
Abstract
Spatial profiles of electron density and temperature obtained from Langmuir probe data in a magnetic mirror plasma experiment using permanent rare-earth magnet stacks show clear signatures of azimuthal or ring currents generated by grad B and curvature drifts. The plasma-generating hot cathode filament is placed within the mirror so that the primary electrons generated with energies sime75 eV are confined by the magnetic mirror effect resulting in a combination of a rapid bounce motion with a slower azimuthal drift whose direction is determined by the orientation of the magnet stacks. A spatial scan using a movable Langmuir probe system shows two peaks of unequal amplitude in the hot electron density profile at locations along the probe path corresponding to phgr = 90° and phgr = 270° where the filament is located at phgr = 0. The position of the stronger peak is consistent with the shorter path in the electron drift direction for the choice of orientation of the magnets. Reversing the magnetic orientation exchanges the locations of the strong and weak hot electron density peaks. The dependence of the ratio of the two peak amplitudes on gas pressure p is consistent with exponential attenuation of the hot electron density along the drift orbit with a mean free path λ mfp ∝ 1/p.
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Keywords
Magnetic mirror plasma , Ring currents , Azimuthal drifts , Movable Langmuir probe , Bi-Maxwellian fit
Citation
McCarthy, P. J. and Knott, S. (2019) 'Signatures of ring currents in a magnetic mirror plasma experiment', Plasma Research Express, 1(4), 045006 (12pp). doi: 10.1088/2516-1067/ab5821