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It is recognized that tokamak plasma disruptions and vertical displacement events, with the attendant appearance of halo currents, are a threat to future experiments such as ITER. Halo currents, flowing between the plasma and the wall, can develop large spatially localized components. Here, we ascribe this to a new instability that can occur in a composite circuit of a magnetized plasma and a solid conductor. The presence of the conductor divides the current perturbation into topologically distinct stable and unstable composite plasma-wall circuits. The plasma paths of such circuits are subject to hydromagnetic motions, which alter circuit geometry and conductivity while self-consistently preserving toroidal and poloidal periodicity. We develop a simple prototype model which illustrates the geometrical aspect of the mechanism. The heterogeneity of the true plasma-wall system is shown to introduce considerable complexity. Our basic concept may underlie a wider class of instabilities and waves.

Additional information

Authors: CALOUTSIS A, UKAEA Fusion, Abingdon, Oxon (GB);GIMBLETT C G, UKAEA Fusion, Abingdon, Oxon (GB)
Bibliographic Reference: Report: UKAEA FUS 393 EN (1998) 19pp.
Availability: Available from the Librarian, UKAEA, Culham Laboratory, Abingdon, Oxon, OX14 3DB (GB)
Record Number: 199810549 / Last updated on: 1998-05-05
Original language: en
Available languages: en
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