On the motion of runaway electrons in momentum space

The suprathermal drag force and the motion of suprathermal electrons in momentum space are analyzed for a multi-component plasma. The calculations of the particle motion are based on the suprathermal Fokker-Planck equation and include relativistic effects. It is found that, owing to pitch angle scattering, the flow patterns in momentum space are more complicated than previously assumed. Simple expressions for the runaway threshold and the perpendicular momentum of relativistic runaways are derived. The acceleration and slowing-down of runaways are also briefly discussed.