Production of ultrahigh ion current densities at skin-layer subrelativistic laser–plasma interaction

Abstract

Some applications of fast ions driven by a short ( 1 ps) laser pulse (e.g. fast ignition of ICF targets, x-ray laser pumping, laboratory astrophysics research or some nuclear physics experiments) require ion beams of picosecond (or shorter) time durations and of very high ion current densities (∼10 10 A cm −2 or higher). A possible way of producing ion beams with such extreme parameters is ballistic focusing of fast ions generated by a target normal sheath acceleration (TNSA) mechanism at relativistic laser intensities. In this paper we discuss another method, where the production of short-pulse ion beams of ultrahigh current densities is possible in a planar geometry at subrelativistic laser intensities and at a low energy ( 1 J) of the laser pulse. This method-referred to as skin-layer ponderomotive acceleration (S-LPA)-uses strong ponderomotive forces induced at the skin-layer interaction of a short laser pulse with a proper preplasma layer in front of a solid target. The basic features of the high-current ion generation by S-LPA were investigated using a simplified theory, numerical hydrodynamic simulations and measurements. The experiments were performed with subjoule 1 ps laser pulses interacting with massive or thin foil targets at intensities of up to 2 × 10 17 W cm −2 . It was found that both in the backward and forward directions highly collimated high-density ion beams (plasma blocks) with current densities at the ion source (close to the target) approaching 10 10 A cm −2 are produced, in accordance with the theory and numerical calculations. These ion current densities were found to be comparable to (or even higher than) those estimated from recent short-pulse TNSA experiments with relativistic laser intensities. Apart from the simpler physics of the laser-plasma interaction, the advantage of the considered method is the low energy of the driving laser pulses allowing the production of ultrahigh-currentdensity ion beams with a high repetition rate. It opens a prospect for unique tabletop experiments in various fields of physical and technological research.

Ion acceleration from intense laser-generated plasma: methods, diagnostics and possible applications

“…Although ions in this regime achieve relatively low kinetic energies, generally below 1 MeV/charge state, it is of special interest in laser ion source applications and high ion emission yields. The second regime, occurring at intensities above 10 15 W/cm 2 , known as the target normal sheath acceleration (TNSA), has the advantage that it allows to accelerate ions to kinetic energies above 1 MeV/charge state [9]. In this case a high electric fi eld is generated at the rear side of a thin irradiated target, due to relativistic electrons escaping from the target and to resulting Coulomb explosion of the target (Fig.…”

Laser-driven generation of fast particles

“…The S-LPA mechanism was actually discovered at the end of the nineties [38], but just recently this mechanism has been relatively well understood and proved by both numerical simulations and experiments [19,20,[39][40][41][42].…”

“…In this method, ions are accelerated at the rear surface of a thin target. The second one is the, so-called, skin-layer ponderomotive acceleration (S-LPA) method [19,20]. In S-LPA, ions are accelerated in front of the target.…”

Z-petawatt driven ion beam radiography development.

“…Low-energy, but high-current ion beams can be produced by the skin-layer ponderomotive acceleration [13] with sub-relativistic intensities.…”