Wave Generation and Heat Flux Suppression in Astrophysical Plasma Systems

Heat flux suppression in collisionless plasmas for a large range of plasma β 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-β) and double-layer-dominated (low-β) 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 (DLs) suppress the heat flux to a mostly constant factor of the free-streaming value once this transition happens. The DL 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 β explored. The range of plasma-βs 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.