Cosmic rays (CRs) are known to be an often energetically significant component of interstellar and intracluster media. The interplay between CRs and the ambient magnetic field can produce observational signatures (e.g. CR isotropy, radio halos of galaxy clusters, etc.) and even impact galactic evolution on large scales (e.g. galactic winds). Modeling these effects has relied on ill-understood and generally unvalidated linear/quasilinear analytical models for the gyroresonant interaction between CRs and magnetic fields. We perform microphysical simulations of the gyroresonant CR streaming instability and discuss implications for modeling the associated large-scale physics.
