Damping of relativistic electron beams by synchrotron radiation

Relativistic electrons emit synchrotron radiation due to their gyro- and gu iding-center motions in a curved magnetic field. In this article, the kinet ic theory of relativistic electron beams is developed to account for radiat ion reaction by including the Abraham-Lorentz reaction force in the kinetic equation. As an application of this theory, the dynamics of runaway electr ons is examined and a steady-state solution is constructed describing a bal ance between acceleration by the electric field, pitch-angle scattering, an d radiation reaction. Furthermore, it is found that a beam of relativistic electrons can be slowed down by the combined effects of pitch-angle scatter ing and radiation reaction. This damping can be more efficient than ordinar y collisional drag, and appears to explain the decay of post-disruption run away currents in the Joint European Torus (JET) [R. D. Gill, Nucl. Fusion 3 3, 1613 (1993)]. (C) 2001 American Institute of Physics.