  The growth and saturation of Buneman-type instabilities is examined with a
particle-in-cell (PIC) simulation for parameters that are representative for
the foreshock region of fast supernova remnant (SNR) shocks. A dense ion beam
and the electrons correspond to the upstream plasma and a fast ion beam to the
shock-reflected ions. The purpose of the 2D simulation is to identify the
nonlinear saturation mechanisms, the electron heating and potential secondary
instabilities that arise from anisotropic electron heating and result in the
growth of magnetic fields. We confirm that the instabilities between both ion
beams and the electrons saturate by the formation of phase space holes by the
beam-aligned modes. The slower oblique modes accelerate some electrons, but
they can not heat up the electrons significantly before they are trapped by the
faster beam-aligned modes. Two circular electron velocity distributions
develop, which are centred around the velocity of each ion beam. They develop
due to the scattering of the electrons by the electrostatic wave potentials.
The growth of magnetic fields is observed, but their amplitude remains low.
