Open Access Publications from the University of California

## Effect of Target Material on Fast Electron Transport

• Author(s): Chawla, Sugreev
An experiment was performed using the Titan laser (150 J, 0.7 ps pulse duration, 1 $\mu$m wavelength) at LLNL on multilayered targets with varying transport layers. A more collimated electron beam was consistently observed using high- or mid-Z transport layers as compared to low Z layers, without a significant loss in forward-going electron energy flux. PIC simulations agreed well with experiments, showing the formation of strong resistive magnetic channels ($\sim$80 MG ) enveloped by a global B-field that collimate initially divergent fast electrons (in high-Z targets). These results illustrated the dynamic competition between stopping and collimation that is essential to understand in order to optimize electron flux levels.
This work has significant implications for fast ignition. At FI conditions, more energy will be injected into the cone tip very quickly, leading to faster ionization and heating rates. Higher atomic number materials may be favorable at these conditions as ionization can continue for a longer period during a $\sim$20 ps FI pulse. These results motivate further computational and experimental work to investigate how multilayer targets can be exploited to maximize fast electron beam collimation whilst minimizing deposition rates.