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A numerical study of strongly nonlinear plasma motion in a magnetic octupole field

Published online by Cambridge University Press:  13 March 2009

H. G. Eriksson
Affiliation:
Department of Technology, Uppsala University, Box 534, S-751 21 Uppsala, Sweden
C. Wahlberg
Affiliation:
Department of Technology, Uppsala University, Box 534, S-751 21 Uppsala, Sweden

Abstract

The strongly nonlinear axisymmetric motion of a z–pinch in an external magnetic octupole field is investigated numerically. A surface-current ideal-MHD approximation of the pinch is used, which allows a ‘contour-dynamics’ formulation of the problem. It is found that the plasma motion in the strongly nonlinear regime results in a collision between the plasma and one (or several) of the X-points. Thereafter, the X-point splits into two magnetic nulls (Y-points), which remain on the plasma surface and between which current reversal occurs. This phenomenon results in a strong force exerted on the outer parts of the plasma and directed towards the centre of the configuration. The force is able to stop the outward plasma motion under certain parameter conditions, which are found to be similar to those observed in experiments on the straight Extrap configuration.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1990

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