Subsonic transport of magnetic flux via a Nernst wave*

The Nernst effect plays a dominant role in the subsonic transport of magnetic flux in hot, dense fusion plasmas, where the temperature diffusivity is much greater than the magnetic diffusivity, as in MagLIF near stagnation. The existing theoretical scalings for the Nernst-dominated magnetic flux losses from hot magnetized fusion plasmas are based on the analysis of self-similar solutions of the full set of plasma transport equations in a planar geometry, for a half-space occupied by the hot magnetized plasma and confined by a fixed cold boundary that may or may not be ablating. The wall roughly emulates the liner or the DT layer in the “ice-burner” MagLIF regime. We have investigated the solutions that do not involve any artificial walls but describe both cold/dense and hot/rarefied regions of the plasma. As the heated cold plasma expands, the heat diffusion proceeds through the material interface that separates cold and hot layers. But the Nernst-transported magnetic flux leaves the material interface behind, propagating into the expanding cold plasma as a narrow front that we call the Nernst wave. We report analytic and numerical solutions involving Nernst waves and describe their effect on magnetic flux and heat losses from the hot plasma.