Description
Ion acceleration is a key phenomenon in relativistic laser-plasma interactions, with applications in ultrafast plasma diagnostics, warm dense matter, or nuclear physics. While standard solid targets are easily implementable and robust, they generate debris and require realignment, hampering high-repetition-rate operation. Gaseous targets are a promising alternative–they are self-regenerating, produce minimal debris, and can deliver various ion species depending on the gas composition–but typically yield ions with broad angular distributions and lower energies than predicted by particle-in-cell (PIC) simulations [1,2]. Since many applications require forward-directed, multi-MeV ion beams, achieving efficient direct acceleration demands precise control of the interaction parameters [3].
We performed PIC simulations of ion acceleration from dense gas jets under multi-petawatt, ultrashort (~fs) irradiation. A parametric scan of laser intensity and pulse duration revealed optimal parameters maximizing on-axis ion cutoff energy to several tens of MeV. We identified an experimentally accessible parameter window to be tested soon at the Apollon (France) and ELI-NP (Romania) laser facilities.
In parallel, we examined the possibility of tailoring the gas density profile to enhance ion acceleration [4]. Gas jet systems typically generate extended (a few 100 µm long), low-to-moderate density ($10^{18}-10^{20}$ cm$^{−3}$) zones that can degrade the laser pulse before it reaches the peak density. To address this, we propose shaping the gas jet using a nanosecond laser prepulse. Hydro-radiative FLASH simulations modeled this process for a Nd:YAG laser pulse (~8 ns, 1 J). Our results indicate that a Laguerre–Gauss laser profile enables an overcritical plasma density ($> 10^{21}$ cm$^{-3}$) to be formed from an initially sub-critical gas jet ($< 10^{20}$ cm$^{-3}$), yielding more favorable conditions for efficient ion acceleration.
References
[1] V. Ospina-Bohórquez et al., Phys. Plasmas 31, 013102 (2024).
[2] V. Ospina-Bohórquez et al., Phys. Rev. Res. 6, 023268 (2024).
[3] J. Bonvalet et al., Phys. Plasmas 28, 113102 (2021).
[4] A. Maitrallain et al., J. Plasma Phys. 90, 965900201 (2024).