Description
Classical transport theory predicts that, in a magnetised, collisional plasma, the heat flux parallel to magnetic field lines is given by Spitzer’s theory of heat conduction for unmagnetised plasmas. Numerous recent theoretical and computational studies have called this prediction into question for weakly collisional magnetised plasmas in which thermal pressure dominates magnetic pressure (so-called high-β plasmas). Such plasmas, notable examples of which include the intra-cluster medium of galaxy clusters and inertial-confinement-fusion deuterium-tritium hotspots, are thought to be susceptible to a host of anisotropy-driven microinstabilities that can suppress parallel heat conduction. Various attempts have been made to construct revised theories of heat conduction in such plasmas, relying on kinetic simulations, but there is a lack of experimental data to benchmark them. In this talk, we report a new experiment at the Orion Laser Facility in which the temporal evolution of the temperature in a high-β, weakly collisional plasma is primarily dependent on the magnitude of the thermal conductivity along its laminar magnetic field. This temperature evolution, along with the plasma’s density and magnetic field, is characterised with a suite of plasma diagnostics: x-ray spectroscopy and imaging, and proton radiography. Our data indicate significant suppression of thermal conduction compared to predictions from Spitzer once stochastic magnetic fluctuations develop. These results have important implications for transport modelling in both astrophysical and laser plasma physics.