Computational modeling of proton acceleration with multi-picosecond and high energy, kilojoule, lasers

Abstract

We use computational modeling to investigate proton beam generation from kilojoule, multi-picosecond laser pulses pertinent to several recently commissioned, large-scale laser facilities. The dependencies of proton acceleration on electron source parameters including pulse duration, temperature, and flux are independently and systematically evaluated. Proton acceleration is found to depend not only on the source size and peak temperature of the injected electrons but also on the rate of increase for a more physical time-varying temperature. Simulations of a 10 ps, sub-relativistic intensity (8 × 1017 W/cm2) at 1 μm wavelength laser pulse show that energetic electrons generated within the expanding under-dense laser-produced plasma sustain the proton acceleration for ∼20 ps. This results in 15 MeV energy gain of the protons, well above what would be predicted based on conventional intensity scalings or what has been observed with shorter pulses. Using this prolonged acceleration, a scheme consisting of a 1 ps and 10 ps double pulse is shown to further boost proton maximum energy.

Production of relativistic electrons at subrelativistic laser intensities

“…For interactions with steep plasma density profiles, the dominant energy transfer mechanism is j×B heating [1,2]. In the presence of plasma densities less than critical (n c ≈ 10 −21 cm −3 ), simulations predict that electrons can gain energy by dephasing from a relativistic-intensity laser field [18][19][20][21][22][23][24][25]. The processes by which electrons dephase from the laser, however, are not well understood at sub-relativistic intensities.…”

Focussing Protons from a Kilojoule Laser for Intense Beam Heating using Proximal Target Structures

“…The electron source method has been applied previously in similar problems 30 and benchmarked against full simulation of the laser 31 . The choice of an electron source with increasing slope temperature that exceeds that predicted by ponderomotive scaling for the laser intensity is a proven method for more accurately simulating proton acceleration from multi-picosecond pulses 38 . Longitudinal and lateral electric field maps were recorded periodically as were all species' densities, temperatures and velocities.…”

Proton beam emittance growth in multipicosecond laser-solid interactions

“…OMEGA EP, for example, is capable of delivering relativistically intense laser pulses (Iλ 2 >10 18 Wcm −2 μm 2 ) with kilojoule energies and multipicosecond pulse durations. Simulations suggest that the multipicosecond interaction will heat plasma electrons beyond the ponderomotive potential of the laser [24][25][26][27]. Indeed, recent experimental results have confirmed that these high energy, multipicosecond laser systems accelerate ions to maximum energies beyond those predicted by traditionally cited scaling laws [28][29][30].…”