Enhanced ion acceleration using the high-energy petawatt PETAL laser

Abstract

The high-energy petawatt PETAL laser system was commissioned at CEA’s Laser Mégajoule facility during the 2017–2018 period. This paper reports in detail on the first experimental results obtained at PETAL on energetic particle and photon generation from solid foil targets, with special emphasis on proton acceleration. Despite a moderately relativistic (<1019 W/cm2) laser intensity, proton energies as high as 51 MeV have been measured significantly above those expected from preliminary numerical simulations using idealized interaction conditions. Multidimensional hydrodynamic and kinetic simulations, taking into account the actual laser parameters, show the importance of the energetic electron production in the extended low-density preplasma created by the laser pedestal. This hot-electron generation occurs through two main pathways: (i) stimulated backscattering of the incoming laser light, triggering stochastic electron heating in the resulting counterpropagating laser beams; (ii) laser filamentation, leading to local intensifications of the laser field and plasma channeling, both of which tend to boost the electron acceleration. Moreover, owing to the large (∼100 μm) waist and picosecond duration of the PETAL beam, the hot electrons can sustain a high electrostatic field at the target rear side for an extended period, thus enabling efficient target normal sheath acceleration of the rear-side protons. The particle distributions predicted by our numerical simulations are consistent with the measurements.

A cylindrical implosion platform for the study of highly magnetized plasmas at LMJ

“…Finally, diagnosing the seed magnetic field is crucial for understanding the conditions of the experiment. For this purpose propose the use of proton deflectometry, in a shot with no gas cylinder (only coil targets), using the PETAL beam 48 to produce and accelerate protons via the Target Normal Sheath Acceleration (TNSA) mechanism 51 . By placing a reference mesh in the protons' path, and recording the imprint of the beam after it traverses the region between the coils, it is possible to obtain an 'image' of the deflections caused by the electric and magnetic fields around the coil targets.…”

Numerical investigation of spallation neutrons generated from petawatt-scale laser-driven proton beams

“…Proton acceleration using PETAL was investigated in quasi-3D geometry with the CALDER-CIRC PIC code [41]. Based on experimental measurements [42], the PETAL laser wave was modeled as two superimposed, time-synchronized Gaussian laser waves. Both propagated along the longitudinal 𝑥-axis, were linearly polarized along the 𝑦-axis, and had a 610 fs FWHM duration.…”

“…cm ,( . Based on hydrodynamic-radiative simulations [42], the electron density profile of the preplasma was taken to evolve as 𝑛 `(𝑥) = 5 𝑛 d exp 5.45 𝑥 150 9. 'g , where the longitudinal position 𝑥 is here expressed in 𝜇m units.…”

“…During the interaction, the laser wave propagates through the extended undercritical preplasma while driving the electrons to relativistic energies through various processes. These have been examined in detail by some of us in a recent study [42], which revealed the importance of stochastic electron heating as a result of stimulated laser backscatter and laser filamentation in the preplasma. After traversing the target, the laser-generated hot electrons form a negatively charged cloud around the backside.…”

Quasi-monoenergetic carbon ions generation from a double-layer target driven by extreme laser pulses

“…For instance, a quasi-monoenergetic proton beams can be generated through combining RPD and laser wake-field acceleration [28]. Experimentally, near 100 MeV proton beam can be obtained by a hybrid acceleration mechanism with the combination of RPD and target normal sheath acceleration using a linearly polarized laser pulse [29][30][31]. However, the laser-to-ion energy conversion efficiency is typically only a few percent and the energy spread is typically Boltzmann distribution in the experiments.…”