Magnetic Cavitation and the Reemergence of Nonlocal Transport in Laser Plasmas

We present the first fully kinetic Vlasov-Fokker-Planck simulations of nanosecond laser-plasma interactions including self-consistent magnetic fields and hydrodynamic plasma expansion. For the largest magnetic fields externally applied to long-pulse laser-gas-jet experiments (12 T) a significant degree of cavitation of the $B$ field ($>40\%$) will be shown to occur from the laser-heated region in under half a nanosecond. This is due to the Nernst effect and leads to the reemergence of nonlocality even if the initial value of the magnetic field strength is sufficient to localize the transport.

Figure 1

Plasma temperature profiles after 440 ps with imposed $B$ fields of 0 T, 2 T, 4 T, and 12 T. The lines labeled “full” use the full equation for $\partial \mathbf{B}/\partial t$. Those labeled “frozen” assume that the magnetic field is frozen to the plasma.

Figure 2

Magnetic field profiles after 440 ps.

Figure 3

The radial heat flows after 440 ps (normalized to the free-streaming limit for the background 20 eV plasma). “VFP” refers to those calculated by the VFP code, “Brag” to those predicted by classical transport theory.

Figure 4

The radial profile of the azimuthal heat flow (normalized as in Fig. 3).

Figure 5

Time evolution of the relative discrepancy of the radial heat flow away from the Braginskii theory.