First demonstration of ARC-accelerated proton beams at the National Ignition Facility

Abstract

New short-pulse kilojoule, Petawatt-class lasers, which have recently come online and are coupled to large-scale, many-beam long-pulse facilities, undoubtedly serve as very exciting tools to capture transformational science opportunities in high energy density physics. These shortpulse lasers also happen to reside in a unique laser regime: very high-energy (kilojoule), relatively long (multi-picosecond) pulse-lengths, and large (10s of micron) focal spots, 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 in the Lawrence Livermore National Laboratory is demonstrated for the first time, and protons of up to 18 MeV are measured using laser irradiation of >1 ps pulse-lengths and quasi-relativistic ($10 18 W/cm 2 ) intensities. This is indicative of a super-ponderomotive electron acceleration mechanism that sustains acceleration over long (multi-picosecond) time-scales and allows for proton energies to be achieved far beyond what the well-established scalings of proton acceleration via TNSA would predict at these modest intensities. Furthermore, the characteristics of the ARC laser (large $100 lm diameter focal spot, flat spatial profile, multi-picosecond, relatively low prepulse) provide acceleration conditions that allow for the investigation of 1D-like particle acceleration. A high flux $ 50 J of laser-accelerated protons is experimentally demonstrated. A new capability in multi-picosecond particle-in-cell simulation is applied to model the data, corroborating the high proton energies and elucidating the physics of multi-picosecond particle acceleration.

Proton beam emittance growth in multipicosecond laser-solid interactions

“…Simulations suggest that the multipicosecond interaction will heat plasma electrons beyond the ponderomotive potential of the laser [24][25][26][27]. Indeed, recent experimental results have confirmed that these high energy, multipicosecond laser systems accelerate ions to maximum energies beyond those predicted by traditionally cited scaling laws [28][29][30].…”

Methods for extremely sparse-angle proton tomography

“…When proton beams are driven by the target normal sheath acceleration (TNSA) mechanism [44] one high-energy short pulse is required per beam, and the number of short pulses available at existing facilities is very limited, with many (for example, the United Kingdom's Orion and Vulcan [45] and OMEGA EP [46] in the United States) providing two short pulses. The National Ignition Facility's Advanced Radiographic Capability system has been demonstrated with four independent beamlets [47,48] and is designed to eventually provide eight [49,50]. Thus, even numbers of projections considered "very sparse" by the wider computed tomography community (75 in Ref.…”

Recent progress in quantifying hydrodynamics instabilities and turbulence in inertial confinement fusion and high-energy-density experiments

“…Efforts are still underway to increase the spatial resolution of the x-ray radiographs with point-projection short pulse wire backlighters [128,129], with the aim of taking advantage of short pulse backlighter capabilities like the advanced radiographic capability (ARC) laser system at the NIF [130] or Petawatt Aquitaine Laser (PETAL) on LMJ [131]. These additional laser beamlines, based on OPCPA (Optical Parametric Chirped Pulse Amplification) technology [132], are extremely useful for generating bright X-ray sources [130] or protons beams [133] used, for example, to probe magnetized HED plasmas [134]. The plasma universe being magnetized and turbulent, one standing question remains as to how to explain the level of the observed magnetic field in the interstellar and intracluster media (ISM and ICM, respectively).…”