Laser-driven collisionless shock acceleration of ions from near-critical plasmas

Abstract

This paper overviews experimental and numerical results on acceleration of narrow energy spread ion beams by an electrostatic collisionless shockwave driven by 1 m (Omega EP) and 10 m (UCLA Neptune Laboratory) lasers in near critical density CH and He plasmas, respectively. Shock waves in CH targets produced high-energy ~50 MeV protons (E/E of ≤30%) and 314 MeV C 6+ ions (E/E of ≤10%). Observation of acceleration of both protons and carbon ions to similar velocities is consistent with reflection of particles off the moving potential of a shock front. For shocks driven by CO 2 laser in a gas jet, ~30 MeV peak in He ion spectrum was detected. Particle-in-cell simulations indicate that regardless of the target further control over its density profile is needed for optimization of accelerated ion beams in part of energy spread, yield and maximum kinetic energy.

Multiple species laser-driven ion-shock acceleration

“…In the multi-species case two shocks are formed, a feature that has not been previously observed in single species and low-Mach number multi-species simulations, but was recently reported at high laser intensities [30,31]. From the theory shown in section 2, we would expect a single shock to form that only reflects protons, the higher charge-to-mass ion species.…”

“…Previous multiple ion species simulations have investigated intricacies that arise, such as instabilities in the upstream plasma due to the streaming of multiple species [28], in idealized low Mach number simulations below the critical Mach number [29], in specific cases to support experimental data [30], and at high laser intensities [31]. Shock formation in plasmas with multiple ion species has only been studied comprehensively for the collisional regime where collective effects drive the separation of ion species [32,33].…”

Laser-driven collisionless shock acceleration of protons from gas jets tailored by one or two nanosecond beams

“…In previous numerical studies, 18,22,35 the plasma density profile was optimized in terms of laser absorption and shock formation with a 10 lm linear ramp at the front side and an exponential slope at the rear side with a scale length L p ¼ 20 lm. However, the gas jets used in experiments have a much broader density profile.…”

Enhanced proton acceleration from laser interaction with curved surface nanowire targets

“…In particular, energetic ion beams have a multitude of promising potential applications in many areas, such as proton radiography (Borghesi et al 2004), tumour therapy (Fourkal et al 2002), materials characterization (Passoni, Fedeli & Mirani 2019;Mirani et al 2021;Boivin et al 2022) and fast ignition in inertial confinement fusion (Tabak et al 1994), etc. Several mechanisms for laser-driven ion acceleration have been developed, including target normal sheath acceleration (TNSA) (Snavely et al 2000;Wilks et al 2001;Mora 2003), radiation pressure acceleration (Robinson et al 2008;Yan et al 2008), collisionless shock acceleration (Xie et al 2019;Tochitsky et al 2020), magnetic vortex acceleration (Bulanov et al 2010;Nakamura et al 2010;Li et al 2022), etc. Among these, TNSA has been studied widely both in simulations and experiments (Maksimchuk et al 2000;Wagner et al 2016;Lv et al 2019).…”