Proton sheet crossing in thin relativistic plasma irradiated by a femtosecond petawatt laser pulse

Accelerating Ions by Crossing Two Ultraintense Lasers in a Near-Critical Relativistically Transparent Plasma

A new scheme of ion acceleration by crossing two ultraintense laser pulses in a near-critical relativistically transparent plasma is proposed. One laser, acting as a trigger, preaccelerates background ions in its radial direction via the laser-driven shock. Another crossed laser drives a comoving snowplow field which traps some of the preaccelerated ions and then efficiently accelerates them to high energies up to a few giga-electron-volts. The final output ion beam is collimated and quasimonoenergetic due to a momentum-selection mechanism. Particle-in-cell simulations and theoretical analysis show that the scheme is feasible and robust.

High-flux neutron generation by laser-accelerated ions from single- and double-layer targets

Contemporary ultraintense, short-pulse laser systems provide extremely compact setups for the production of high-flux neutron beams, such as those required for nondestructive probing of dense matter, research on neutron-induced damage in fusion devices or laboratory astrophysics studies. Here, by coupling particle-in-cell and Monte Carlo numerical simulations, we examine possible strategies to optimise neutron sources from ion-induced nuclear reactions using 1-PW, 20-fs-class laser systems. To improve the ion acceleration, the laser-irradiated targets are chosen to be ultrathin solid foils, either standing alone or preceded by a plasma layer of near-critical density to enhance the laser focusing. We compare the performance of these single- and double-layer targets, and determine their optimum parameters in terms of energy and angular spectra of the accelerated ions. These are then sent into a converter to generate neutrons via nuclear reactions on beryllium and lead nuclei. Overall, we identify configurations that result in neutron yields as high as $$\sim 10^{10}\,{\mathrm{n}}\,{\mathrm{sr}}^{-1}$$ ∼ 10 10 n sr - 1 in $$\sim 1$$ ∼ 1 -cm-thick converters or instantaneous neutron fluxes above $$10^{23}\,{\mathrm{n}}\,{\mathrm{cm}}^{-2}\,{\mathrm{s}}^{-1}$$ 10 23 n cm - 2 s - 1 at the backside of $$\lesssim 100$$ ≲ 100 -$$\upmu$$ μ m-thick converters. Considering a realistic repetition rate of one laser shot per minute, the corresponding time-averaged neutron yields are predicted to reach values ($$\gtrsim 10^7\,{\mathrm{n}} \,{\mathrm{sr}}^{-1}\,{\mathrm{s}}^{-1}$$ ≳ 10 7 n sr - 1 s - 1 ) well above the current experimental record, and this even with a mere thin foil as a primary target. A further increase in the time-averaged yield up to above $$10^8\,{\mathrm{sr}}^{-1}\,{\mathrm{s}}^{-1}$$ 10 8 sr - 1 s - 1 is foreseen using double-layer targets.

Temperature evolution of dense gold and diamond heated by energetic laser-driven aluminum ions

Recent studies have shown that energetic laser-driven ions with some energy spread can heat small solid-density samples uniformly. The balance among the energy losses of the ions with different kinetic energies results in uniform heating. Although heating with an energetic laser-driven ion beam is completed within a nanosecond and is often considered sufficiently fast, it is not instantaneous. Here we present a theoretical study of the temporal evolution of the temperature of solid-density gold and diamond samples heated by a quasimonoenergetic aluminum ion beam. We calculate the temporal evolution of the predicted temperatures of the samples using the available stopping power data and the SESAME equation-of-state tables. We find that the temperature distribution is initially very uniform, which becomes less uniform during the heating process. Then, the temperature uniformity gradually improves, and a good temperature uniformity is obtained toward the end of the heating process.

Energetic spin-polarized proton beams from two-stage coherent acceleration in laser-driven plasma

We propose a scheme to overcome the great challenge of polarization loss in spin-polarized ion acceleration. When a petawatt laser pulse penetrates through a compound plasma target consisting of a double layer slab and prepolarized hydrogen halide gas, a strong forward moving quasistatic longitudinal electric field is constructed by the self-generated laser-driven plasma. This field with a varying drift velocity efficiently boosts the prepolarized protons via a two-stage coherent acceleration process. Its merit is not only achieving a highly energetic beam but also eliminating the undesired polarization loss of the accelerated protons. We study the proton dynamics via Hamiltonian analyses, specifically deriving the threshold of triggering the two-stage coherent acceleration. To confirm the theoretical predictions, we perform three-dimensional PIC simulations, where unprecedented proton beams with energy approximating half GeV and polarization ratio ∼ 94% are obtained.