Formation of percursor whistler mode plasma turbulence in parallel shock waves

The beam-whistler and ion cyclotron instabilities are proposed as principal mechanisms for the generation of precursor turbulence in shock waves propagating along the constant magnetic field. The beam is formed from ions which are reflected from a potential barrier whose existence inside the shock layer is assumed. We find that these reflected beam particles drive unstable a spatial continuum of zero group velocity (with respect to the shock front) precursor whistler waves.