  Streaming cosmic rays can power the exponential growth of a seed magnetic
field by exciting a non-resonant instability that feeds on their bulk kinetic
energy. By generating the necessary turbulent magnetic field, it is thought to
play a key role in the confinement and acceleration of cosmic rays at shocks.
In this work we present hybrid-Particle-In-Cell simulations of the non-resonant
mode including Monte Carlo collisions, and investigate the interplay between
the pressure anisotropies produced by the instability and particle collisions
in the background plasma. Simulations of poorly ionized plasmas confirm the
rapid damping of the instability by proton-neutral collisions predicted by
linear fluid theory calculations. In contrast we find that Coulomb collisions
in fully ionized plasmas do not oppose the growth of the magnetic field, but
under certain conditions suppress the pressure anisotropies and actually
enhance the magnetic field amplification.
