The effect of increasing prepulse energy levels on the energy spectrum and coupling into forward-going electrons is evaluated in a cone-guided fast-ignition relevant geometry using cone-wire targets ...irradiated with a high intensity (10(20) W/cm(2)) laser pulse. Hot electron temperature and flux are inferred from Kα images and yields using hybrid particle-in-cell simulations. A two-temperature distribution of hot electrons was required to fit the full profile, with the ratio of energy in a higher energy (MeV) component increasing with a larger prepulse. As prepulse energies were increased from 8 mJ to 1 J, overall coupling from laser to all hot electrons entering the wire was found to fall from 8.4% to 2.5% while coupling into only the 1-3 MeV electrons dropped from 0.57% to 0.03%.
A novel time-resolved diagnostic is used to record the critical surface motion during picosecond-scale relativistic laser interaction with a solid target. Single-shot measurements of the specular ...light show a redshift decreasing with time during the interaction, corresponding to a slowing-down of the hole boring process into overdense plasma. On-shot full characterization of the laser pulse enables simulations of the experiment without any free parameters. Two-dimensional particle-in-cell simulations yield redshifts that agree with the data, and support a simple explanation of the slowing-down of the critical surface based on momentum conservation between ions and reflected laser light.
The ion-Weibel instability is a leading candidate mechanism for the formation of collisionless shocks observed in may astrophysical systems. Experimental and computational studies have shown that the ...ion-Weibel instability drives current filamentation in interpenetrating plasma flows 1 , 2 with the capability to mediate collisionless shock formation and subsequent particle acceleration 3 in the lab. The present work focuses on the study of nonlinear ion-Weibel evolution under various plasma conditions through utilization of different ion species and experimental geometries. Temporally varying plasma condition are determined using benchmarked FLASH simulations. Path-integrated B-field distributions are retrieved from experimental proton images in all cases and Fourier analyzed to quantify the dominant filament scale-size and estimate the B-field strength. This new analysis methodology demonstrates that the first ~400ps of plasma interpenetration sets the spectral characteristics of ion-Weibel filamentation, and that underlying plasma conditions later in time do not significantly alter nonlinear filament evolution.
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