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(TH/8-1) On the Physics of Runaway Particles in JET and MAST

P. Helander¹⁾, L.-G. Eriksson²⁾, F. Andersson³⁾, R.J. Akers¹⁾, C. Byrom¹⁾⁴⁾, C.G. Gimblett¹⁾, M.R. Tournianski^1)
 
1) UKAEA, Culham Science Centre, Abingdon, United Kingdom
²⁾ Association EURATOM-CEA sur la Fusion, CEA Cadarache, France
³⁾Dept. of Electromagnetics, Chalmers University of Technology, Göteborg, Sweden
⁴⁾Dept. of Physics, UMIST, Manchester, United Kingdom

Abstract.  In the first part of this paper, a kinetic theory is developed to explain observations of the damping of post-disruption runaway electron currents in JET. It is shown that the damping of the current carried by relativistic eletrons following a disruption cannot be explained by ordinary collisional friction. Instead, pitch-angle scattering and the subsequent emission of synchrotron radiation play the key role in regulating the current. These effects are treated mathematically by including the Abraham-Lorentz force in the kinetic equation and solving the resulting initial-value problem by analytical approximation and by Monte Carlo simulation. The second part of the paper is devoted to explaining the origin of suprathermal ions observed in Ohmic MAST discharges following internal reconnection events. It is shown that these observations can be understood in terms of runaway ion acceleration - a phenomenon predicted by Furth and Rutherford in 1972, but not commonly noted in tokamaks.

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