Diffusion of runaway electrons in a tokamak

It is shown that the presence of a sufficient number of accelerated electrons in a plasma leads to anomalous diffusion of the electrons across the magnetic field. The diffusion of the particles is associated with the presence of waves driven unstable by the runaway electrons via anomalous and Doppler effect. Expressions are obtained for the diffusion coefficient, the oscillation spectrum and the distribution function of the accelerated electron beam.