DYNAMICS OF RUNAWAY ELECTRONS IN THE MAGNETIC-FIELD OF A TOKAMAK

An energy cap of runaway electrons is found experimentally by observin g their bremsstrahlung spectra in the ASDEX tokamak. This observation is explained by analyzing the dynamics of runaway electrons, including acceleration in the toroidal electric field, deceleration due to sync hrotron radiation losses, collisions with plasma particles, and a reso nance between gyromotion and magnetic field ripple of the tokamak. For the dynamics of runaway electrons a Fokker-Planck equation in momentu m space is developed.