Ion acceleration in electrostatic collisionless shock: on the optimal density profile for quasi-monoenergetic beams

Abstract

A numerical study on ion acceleration in electrostatic shock waves is presented, with the aim of determining the best plasma configuration to achieve quasimonoenergetic ion beams in laser-driven systems. It was recently shown that tailored near-critical density plasmas characterized by a long-scale decreasing rear density profile lead to beams with low energy spread [F. Fiúza et al., Physical Review Letters 109, 215001 (2012)]. In this work, a detailed parameter scan investigating different plasma scale lengths is carried out. As result, the optimal plasma spatial scale length that allows for minimizing the energy spread while ensuring a significant reflection of ions by the shock is identified. Furthermore, a new configuration where the required profile has been obtained by coupling micro layers of different densities is proposed. Results show that this new engineered approach is a valid alternative, guaranteeing a low energy spread with a higher level of controllability.

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

“…For simplicity, the near-critical plasma is assumed to be composed of only hydrogen ions H + and electrons both with the initial temperature of 1 keV. The plasma electron density has a tailored profile with a rapid 10 μm linear rise starting at x=−10 μm to the peak density 12n c at x=0 and then followed by an exponentially falling with 5 μm scale length, which satisfies the optimized density profile of CSA [27,28,35]. The high-Z solid tube is assumed to have a high electron density of 50n c , tube length of 300 μm and wall thickness of 1 μm.…”

“…So a strong collisionless shock with the Mach number > M 1.6 and the large shock velocity v sh >v hb is formed. Based on this model, the required laser and target matching condition for production of high-quality ion beams by CSA has been given in [27,28,35], which, however, is under the assumption of the reduced one-dimensional geometry. The specific optimal tailored density profile required for launching the shock is proposed in order to both avoid strong TNSA field that broadens the energy spread and ensure uniform plasma heating [27,28,35].…”

“…Based on this model, the required laser and target matching condition for production of high-quality ion beams by CSA has been given in [27,28,35], which, however, is under the assumption of the reduced one-dimensional geometry. The specific optimal tailored density profile required for launching the shock is proposed in order to both avoid strong TNSA field that broadens the energy spread and ensure uniform plasma heating [27,28,35]. Currently, CSA has been demonstrated experimentally by using CO 2 lasers [26,36], where the wavelength is at 10.6 μm, the spot size is very large and the intensity is rather low.…”

Collisionless shock acceleration in the corona of an inertial confinement fusion pellet with possible application to ion fast ignition

“…It has been recently suggested that ignition could be achieved with ions generated via collisionless shocks excited directly in the plasma corona surrounding the compressed pellet [10][11][12][13][14][15][16][17]. Indeed laser-driven shock waves provide an efficient mechanism to accelerate highquality ions with average energies of some MeVs [18][19][20][21][22][23][24][25][26]. Furthermore, compared to TNSA the scheme seems advantageous, not only because of the lower energy spread and divergence of the ions [25], but also because exciting the shock in the corona plasma would eliminate the need for an external target, thus reducing the distance between the ion source and the core.…”

Interplay between the Weibel instability and the Biermann battery in realistic laser-solid interactions

“…Recent developments in laser technology (intensities in excess of 10 19 W/cm 2 with laser pulse durations shorter than 1 ps and high-resolution diagnostics) open the possibility to probe such processes through laser-solid interactions [19,[21][22][23][24]. In these experiments, the magnetic field generation is often attributed to the Biermann battery [20,25,26].…”