Quasi-monoenergetic ion beam acceleration by laser-driven shock and solitary waves in near-critical plasmas

Abstract

Ion acceleration in near-critical plasmas driven by intense laser pulses is investigated theoretically and numerically. A theoretical model has been given for clarification of the ion acceleration dynamics in relation to different laser and target parameters. Two distinct regimes have been identified, where ions are accelerated by, respectively, the laser-induced shock wave in the weakly driven regime (comparatively low laser intensity) and the nonlinear solitary wave in the strongly driven regime (comparatively high laser intensity). Two-dimensional particle-in-cell simulations show that quasi-monoenergetic proton beams with a peak energy of 94.6 MeV and an energy spread 15.8% are obtained by intense laser pulses at intensity I0 = 3 × 1020 W/cm2 and pulse duration τ = 0.5 ps in the strongly driven regime, which is more advantageous than that got in the weakly driven regime. In addition, 233 MeV proton beams with narrow spread can be produced by extending τ to 1.0 ps in the strongly driven regime.

High-flux high-energy ion beam production from stable collisionless shock acceleration by intense petawatt-picosecond laser pulses

“…And figure 4 shows the (x, px) distribution of ions at corresponding time steps. At early time t=0.9 ps, because of the strong radiation pressure exerted on the plasma, in both cases, electrons and ions are piled up forward, forming a density spike with the similar maximum values of around 17n c (see figure 2(g)), which means the density ratio between the spike and the undisturbed plasma is N 2 /N 1 ≈4.2, larger than the required downstream to upstream density ratio condition [30] for formation of a collisionless shock. Furthermore, a significant number of hot electrons are generated by the J×B heating of the laser, and recirculate through the whole target and heating the target efficiently to have the average electron temperature of T e ≈4.3 MeV, as seen in figure 5(a) for both cases.…”

“…Because of the thermal expansion and the density drops of the plasma profile, the plasma becomes transparent to the laser, so the laser-plasma interaction surface actually disappears and the HB process terminates when the shock is formed. Here, in order to obtain large shock velocity and eventually high ion energy, the laser is allowed to partially penetrate to efficiently heat the upstream plasma through choosing a proper initial peak density [30]. From the (x, px) phase space, we can also see that the significant shock structure forms behind the density peak at x=60 μm and t=1.8 ps (figures 4(b) and (e)), while only ions from HB reflection is seen at earlier time t=0.9 ps (figures 4(a) and (d)).…”

“…ion-acoustic shocks, are a consequence of non-linear wave steepening and wave breaking of ion-acoustic modes in plasma and are more relevant for laboratory experiments [21][22][23][24][25]. Different from TNSA and RPA, collisionless shock acceleration (CSA) [26][27][28][29][30] has been proposed as an alternative method for production of high-quality ion beams for comparatively long laser pulses. In CSA, the laser pulse launches a collisionless electrostatic shock wave in near-critical density plasmas, and the shock can continuously reflecting a fraction of the background ions as it propagates through the plasma due to the strong electrostatic field associated with the shock front.…”

Maintaining stable radiation pressure acceleration of ion beams via cascaded electron replenishment

“…Most applications require high-energy ion beams with a monoenergetic spectrum, small divergence and large particle number. Several mechanisms of laser ion acceleration are proposed, including target normal sheath acceleration (TNSA) [7,8], radiation pressure acceleration (RPA) [9][10][11][12][13], shock acceleration [14][15][16] and others.…”

Generation of quasi-monoenergetic heavy ion beams via staged shock wave acceleration driven by intense laser pulses in near-critical plasmas

“…Shock wave acceleration (SWA) [7][8][9] by ion reflection in near-critical plasmas is a promising candidate as a source of high quality ion beam. For the SWA in near-critical plasmas, the ions are continuously reflected to twice of the shock velocity during the shock wave stable propagation, resulting in production of intense quasimonoenergetic ion beam with comparatively high particle number.…”