Development of a laser wakefield acceleration platform at the National Ignition Facility*

We present the development of a laser-wakefield electron acceleration 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, 10$^{\mathrm{18}}$ W/cm$^{\mathrm{2}}$ intensity laser pulse is focused on a gas target with a plasma electron density of about 10$^{\mathrm{19}}$ cm$^{\mathrm{-3}}$, electrons are accelerated to multi-100 MeV energies by the interplay of self-modulated laser wakefield and direct laser acceleration. Applications include hard x-ray sources using betatron, Compton scattering and bremsstrahlung mechanisms. We performed experiments with the OMEGA-EP short pulse focused at intensities around 10$^{\mathrm{18}}$ W/cm$^{\mathrm{2}}$ onto a 3 mm plastic gas tube filled with helium at atmospheric pressure, as well as with the ARC beam at LLNL in similar conditions. The gas tubes are closed with 1 \textmu m thick mylar windows that are blown off with long pulses 5-10 ns before the short pulse. We measured the plasma density at the entrance of the gas tube with the 4-omega probe diagnostic at OMEGA-EP and Optical Thomson Scattering at NIF. EPPS (electron proton positron spectrometer), measured accelerated electron energies in the 10-150 MeV range.