H. S. McLean | Searcharxiv

arXiv2019

Sustained neutron production from a sheared-flow stabilized Z-pinch

The sheared-flow stabilized $Z$-pinch has demonstrated long-lived plasmas with fusion-relevant parameters. This Letter presents the first experimental results demonstrating sustained, quasi-steady-state neutron production from the Fusion $Z$-pinch Experiment (FuZE), operated with a mixture of 20% deuterium/80% hydrogen by volume. Neutron emissions lasting approximately $5~μ$s are reproducibly observed with pinch currents of approximately $200$ kA during an approximately $16~μ$s period of plasma quiescence. The average neutron yield is estimated to be $\left ( 1.25\pm 0.45 \right )\times 10^{5}$ neutrons/pulse and scales with the square of the deuterium concentration. Coincident with the neutron signal, plasma temperatures of $1-2$ keV, and densities of approximately $10^{17}$ cm$^{-3}$ with $0.3$ cm pinch radii are measured with fully-integrated diagnostics.

physics.plasm-ph↗

arXiv2018

High-angle Deflection of the Energetic Electrons by a Voluminous Magnetic Structure in Near-normal Intense Laser-plasma Interactions

The physics governing electron acceleration by a relativistically intense laser are not confined to the critical density surface, they also pervade the sub-critical plasma in front of the target. Here, particles can gain many times the ponderomotive energy from the overlying laser, and strong fields can grow. Experiments using a high contrast laser and a prescribed laser pre-pulse demonstrate that development of the pre-plasma has an unexpectedly strong effect on the most energetic, super-ponderomotive electrons. Presented 2D particle-in-cell simulations reveal how strong, voluminous magnetic structures that evolve in the pre-plasma impact high energy electrons more significantly than low energy ones for longer pulse durations and how the common practice of tilting the target to a modest incidence angle can be enough to initiate strong deflection. The implications are that multiple angular spectral measurements are necessary to prevent misleading conclusions from past and future experiments.

physics.plasm-ph↗