First Demonstration of ARC-Accelerated Proton Beams at the National Ignition Facility

New short-pulse Kilojoule-Petawatt lasers such as GEKKO-LFEX, LMJ-PETAL, OMEGA-EP, and NIF-ARC that have recently come online, and which are coupled to versatile large-scale, many-beam long-pulse facilities, undoubtedly serve as very exciting and promising tools to capture transformational science opportunities in HED physics. These particular short-pulse lasers also happen to reside in a unique laser regime: very high-energy (kJ) and relatively long (multi-picosecond) pulse-lengths, where their use in driving energetic particle beams is largely unexplored. Proton acceleration via Target Normal Sheath Acceleration (TNSA) using the Advanced Radiographic Capability (ARC) short-pulse laser at the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory is demonstrated for the first time, and protons of up to 20 MeV are measured using laser irradiation of > 1 ps pulse-lengths, and quasi-relativistic intensities. This is indicative of a super-ponderomotive acceleration mechanism that sustains acceleration over long (multi-ps) time-scales and allows for proton energies to reach beyond well-established TNSA scalings at these modest intensities. Furthermore, the characteristics of the ARC laser (large ~80 µm focal spot, flat spatial profile, multi-ps, low pre-pulse), provide conditions that allow for the investigation of the 1D-physics of particle acceleration. A high laser-to-proton conversion efficiency is experimentally demonstrated, resulting in a record flux (~ 80 J) of laser-accelerated protons. A new capability in multi-ps PIC (particle-in-cell) simulation is applied to model the data, corroborating the high proton energies and elucidating the physics of multi-ps particle acceleration.