In a space plasma there are few neutral particles.  The pressure is close to a vacuum.  So in general a plasma will be colllisionless.  Heat will flow from the hot surface such as the sun’s surface to a cold surface, further out in space.  The magnetic fields are generated by current flows but the magnitude of the magnetic fields will be small.  To study the heat flow in such weakly magnetized collisionless plasmas in the presence of an imposed temperature gradient along an ambient magnetic field particle-in-cell simulations are very effective. The particle in cell codes tract particles in fields self-consistently generated by the average of particles in many cells. The codes can be one dimensional, two dimensional and even three dimensional. However the cost of running the code increase rapidly with the increase in dimensions.

In this paper a two dimensional particle in cell code is used to study two thermal reservoirs at different temperatures driving an electron heat flux that destabilizes off-angle whistler-type modes. The whistlers grow to large amplitude and resonantly scatter the electrons, significantly reducing the heat flux. A surprise is that the resulting steady state heat flux is largely independent of the thermal gradient. The rate of thermal conduction is instead controlled by the finite propagation speed of the whistlers, which act as mobile scattering centers that convect the thermal energy of the hot reservoir. The results are relevant to thermal transport in high beta astrophysical plasmas such as the Intracluster Medium and low-rate accretion flows.