Pitch angle scattering and synchrotron radiation of relativistic runaway electrons in tokamak stochastic magnetic fields

In a recent work [J. R. Martin-Solis and R. Sanchez, Phys. Plasmas 13, 012508 (2006)], the increase that the presence of stochastic magnetic fields causes on the synchrotron radiation losses of relativistic runaway electrons was quantified using a guiding-center approximation. Here, we complete those studies by considering instead the mechanism which dominates the interaction at the gyromotion level. It is shown that, under typical tokamak conditions, the resonant cyclotron interaction with high enough parallel (to the magnetic field) wave numbers (k∥) modes can create, even for moderate magnetic fluctuation levels, an upper bound on the runaway energy. Implications for disruption-generated runaway electrons will be also discussed.

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