Measurement of Cross-Magnetic-Field Heat Transport in a Pure Ion Plasma

Abstract

Cross-magnetic-field heat transport in a quiescent pure ion plasma is found to be diffusive and to be dominated by long-range collisions with impact parameters up to a Debye length. The measured thermal diffusivity $\ensuremath{\chi}$ agrees within a factor of 2 with the long-range prediction ${\ensuremath{\chi}}_{L}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.49n\overline{v}{b}^{2}{\ensuremath{\lambda}}_{D}^{2}$ over a range of ${10}^{3}$ in temperature, $50$ in density, and 4 in magnetic field. This thermal diffusivity is independent of magnetic field strength, and is observed to be up to 100 times larger than the classical diffusivity. These long-range collisions are typically dominant in unneutralized plasmas, and may also contribute to electron heat transport in neutral plasmas.