Abstract: Heat flux suppression in collisionless plasmas for a large range of
plasma beta is explored using two-dimensional particle-in-cell
simulations with a strong, sustained thermal gradient. We find that a
transition takes place between whistler-dominated (high-beta) and
double-layer-dominated (low-beta) heat flux suppression. Whistlers
saturate at small amplitude in the low beta limit and are unable to
effectively suppress the heat flux. Electrostatic double layers suppress
the heat flux to a mostly constant factor of the free streaming value
once this transition happens. The double layer physics is an example of
ion-electron coupling and occurs on a scale of roughly the electron
Debye length. The scaling of ion heating associated with the various
heat flux driven instabilities is explored over the full range of
beta explored. The range of plasma-betas studied in this work
makes it relevant to the dynamics of a large variety of astrophysical
plasmas, including the intracluster medium of galaxy clusters, hot
accretion flows, stellar and accretion disk coronae, and the solar wind.