Measuring heat flux from collective Thomson scattering with non-Maxwellian distribution functions
R. J. Henchen, M. Sherlock, W. Rozmus, J. Katz, P. E. Masson-Laborde, D. Cao, J. P. Palastro, and D. H. Froula
Abstract
Heat flux was measured in coronal plasmas using collective Thomson scattering from electron-plasma waves. A laser-produced plasma from a planar aluminum target created a temperature gradient along the target normal. Thomson scattering probed electron-plasma waves in the direction of the temperature gradient with phase velocities relevant to heat flux. The heat-flux measurements were reduced from classical values inferred from the measured plasma conditions in regions with large temperature gradients and agreed with classical values for weak gradients. In regions where classical theory was invalid, the heat flux was determined by reproducing the measured Thomson-scattering spectra using electron distribution functions consistent with nonlocal thermal transport. Full-scale hydrodynamic simulations using both flux-limited thermal transport (FLASH) and the multigroup nonlocal Schurtz, Nicolaï, and Busquet models underestimated the heat flux at all locations.
