Stability of an astrophysical plasma near the onset of electron runaway

The time-dependent behaviour of a homogeneous plasma in a weak electric field near the onset of runaway of electrons is studied for astrophysical applications. The relativistic Boltzmann equation is used to calculate the particle distribution function. It is shown that the plasma is stable against electric field fluctuations in the onset region for runaway, provided that the global behaviour of the System is determined by the magnetic field structure.