Super-Alfv\'{e}nic Magnetic Field Fluctuations Generated from Low-Density, Magnetized Laser-Plasma Expansions

In recent experiments at the Trident Laser Facility, at the Los Alamos National Laboratory (LANL), the three beam configuration and a pulsed Helmholtz coil were utilized to investigate laser-driven, magnetized shocked plasmas. The $56$ cm, $4.2$ kJ pulsed Helmholtz coil was used to create a $0.1-1.0$ kG magnetic field over an experimental volume of $\sim4\times10^{3}$ cm$^{3}$. Two sequential laser pulses, spaced $1.0-10.0$ $\mu$s apart, were used to ablate a CH or graphite target that was imbedded in the field. The first laser pulse created an ambient magnetized plasma and the second laser pulse created a debris plasma to shock the ambient plasma. The third laser pulse was frequency-doubled and employed for Thomson scattering measurements to characterized the ambient plasma density ($10^{13}-10^{15}$ cm$^{-3}$) and electron temperature ($10-50$ eV). An array of single-axis, $1$ mm b-dot probes were used to measure magnetic field compression, expulsion, and fast-diffusion inside and around the diamagnetic cavity formed by the laser-plasma expansion. A magnetic field compression pulse in the shocked plasma was observed to separate and propagate away from the leading edge of the diamagnetic cavity at an Alfv\'{e}nic Mach number on the order of $10$ (M$_{A}\sim10$).