  Supernova remnant (SNR) blast shells can reach the flow speed $v_s = 0.1 c$
and shocks form at its front. Instabilities driven by shock-reflected ion beams
heat the plasma in the foreshock, which may inject particles into diffusive
acceleration. The ion beams can have the speed $v_b \approx v_s$. For $v_b \ll
v_s$ the Buneman or upper-hybrid instabilities dominate, while for $v_b \gg
v_s$ the filamentation and mixed modes grow faster. Here the relevant waves for
$v_b \approx v_s$ are examined and how they interact nonlinearly with the
particles. The collision of two plasma clouds at the speed $v_s$ is modelled
with particle-in-cell (PIC) simulations, which convect with them magnetic
fields oriented perpendicular to their flow velocity vector. One simulation
models equally dense clouds and the other one uses a density ratio of 2. Both
simulations show upper-hybrid waves that are planar over large spatial
intervals and that accelerate electrons to $\sim$ 10 keV. The symmetric
collision yields only short oscillatory wave pulses, while the asymmetric
collision also produces large-scale electric fields, probably through a
magnetic pressure gradient. The large-scale fields destroy the electron phase
space holes and they accelerate the ions, which facilitates the formation of a
precursor shock.
