  Despite being energetically important, the effect of cosmic rays on the
dynamics of the interstellar medium (ISM) is assumed to be negligible because
the cosmic ray energy diffusion coefficient parallel to the magnetic field is
relatively large. Using numerical simulations, we explore how variation of the
cosmic ray diffusion coefficient as a function of gas temperature could impact
the dynamics of the ISM. We create a two-zone model of cosmic ray transport,
reflecting the strong damping of the small scale magnetic field fluctuations,
which scatter the cosmic rays, in a gas with low ionization. The variable
diffusion coefficient allows more cold gas to form. However, setting the
diffusion coefficient at a critical value in the warm phase allows the cosmic
rays to adjust the kinetic energy cascade. Specifically, we show the slope of
the cascade changes for motion perpendicular to the mean magnetic field,
whereas kinetic energy parallel to the magnetic field is reduced equally across
inertial scales. We show that cosmic ray energization (or reacceleration) comes
at the expense of total radiated energy generated during the formation of a
cold cloud. We also show that our two-zone model of cosmic ray transport is
capable of matching estimates of the grammage for some paths through the
simulation, but full comparison of the grammage requires simulating turbulence
in a larger volume.
