Fast advection of magnetic fields by hot electrons

Experiments where a laser generated proton beam is used to probe the megagauss strength self-generated magnetic fields from a nanosecond laser interaction with an aluminum target are presented. At intensities of $10^{15} \; \rm{Wcm}^{-2}$ and under conditions of significant fast electron production and strong heat fluxes, the electron mean-free-path is long compared with the temperature gradient scale-length and hence non-local transport is important for the dynamics of the magnetic field in the plasma. The hot electron flux transports self-generated magnetic fields away from the focal region through the Nernst effect [1] at significantly higher velocities than the fluid velocity. Two-dimensional implicit Vlasov-Fokker-Planck modeling shows that the Nernst effect allows advection and self-generation transports magnetic fields at significantly faster than the ion fluid velocity, $v_N/c_s\approx10$.\\[4pt] [1] A.~Nishiguchi \textit{et al.}, Phys.\ Rev.\ Lett., \textbf{53}, 262 (1984).