Microcoulomb electron beams from self-modulated laser wakefield acceleration at the National Ignition Facility

We developed a laser-wakefield electron acceleration (LWFA) experimental capability by focusing one beamlet (1 ps, 250 J) of the Advanced Radiographic Capability (ARC, LLNL) onto a gas tube target filled with helium. When a picosecond laser pulse (intensity around 10$^{\mathrm{18\thinspace }}$W/cm$^{\mathrm{2}})$, is focused on a gas target with an electron density of about 10$^{\mathrm{19}}$ cm$^{\mathrm{-3}}$, electrons are accelerated to multi-100 MeV energies by the interplay of direct laser acceleration and self-modulated LWFA. Such beams can be used for the development of x-ray sources using betatron, Compton scattering and bremsstrahlung mechanisms. Experiments were conducted at the National Ignition facility with the ARC short pulse focused at intensities around 10$^{\mathrm{18}}$ W/cm$^{\mathrm{2}}$ onto 3 mm plastic gas tubes filled with helium at atmospheric pressure. The tubes are closed with 1 \textmu m thick mylar windows that are blown off with long pulses 5-10 ns before the short pulse. The newly developed W-NEPPS (Wakefield NIF Electron Proton Positron Spectrometer), measured electron energies of 10-150 MeV, with charges approaching a microcoulomb. Performed under the auspices of the U.S. DOE by LLNL under Contract No. DE-AC52-07NA27344, supported by the DOE Office Science Early Career Research Program (FES) SCW 1575-1. LLNL-ABS-811953