Description
Laser-driven ion accelerators have become more prominent in many fields of applications and are reaching higher intensities regularly with petawatt intensities over 10$^{21}$ W.cm$^{-2}$ at the current time. Laser-driven ions beams are short, low-emittance and are useful for applications such as warm dense matter study, fusion energy research, time-resolved transient fields probing or even radiation oncology. All these applications necessitate high proton energies and highly controllable ion spectra and spatial distribution, which is made possible by specialist targets and tailored temporal laser pulse shapes.
In order to shape targets before the main laser pulse, it is important to study the sub-relativistic intensities laser-plasma interactions at play for generating a pre-expanded target. This shaping is made to optimise the transfer of energy between the main pulse and the target. The steepness and length of the density profile of the target is the decisive parameter to determine the acceleration scheme of the main interaction [1].
However, the physics of laser plasma interaction at the intensity and duration of the prepulse is at the boundary within the hydrodynamical and Particle-in-Cell models due to the overlap of different absorption mechanisms as well as different time-scale phenomenologies. It is why the numerical approach needs an hybrid use of both hydrodynamical and Particle-in-Cell simulations.
A set of experiment was performed at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) to study the controlled pre-expansion of targets within the framework of an acceleration optimization study. In order to analyse the impact of the prepulse on the acceleration efficiency, a hybrid study via 2D PIConGPU and FLASH simulations was performed. This study validated a simulation chain from laser absorption of short prepulses to the target expansion over 100s of ps and showed a great agreement with the exper imental results. The large amount of density profiles obtained allows us to now scan the impact on the prepulse energy, main pulse delay and orientation on the acceleration processes.
References
[1] M. Rehwald et al, Nature Com. 14, 4009 (2023)