First experimental results from the high-energy petawatt PETAL laser system

The PETAL (PETawatt Aquitaine Laser) project, commissioned during the 2017-2018 period, added a high-energy multi-petawatt beam to the Laser Mégajoule (LMJ) in France. Now completed, the laser system can deliver pulses in the kilojoule-picosecond range, synchronized with the nanosecond LMJ beams at the target chamber center.

Raffestin et al. report on the first experimental results obtained at PETAL in 2018 from the generation of high-energy particles and radiation from laser-solid interactions. Despite the intensity being only moderately relativistic, the characteristics of the laser led to the acceleration of protons to unexpectedly high energies ranging between 30 and 50 mega-electronvolts.

“Large amounts of high energy ions produced by laser are ideally suited for probing matter under extreme conditions. In different laboratories, upstream research is performed to apply ion acceleration by laser to future applications such as medical treatment or radio isotope production,” said author Didier Raffestin.

Several diagnostics, including SEPAGE (Spectromètre Electron Proton A Grande Energie) and SESAME (Spectromètre ElectronS Angulaires Moyenne Energies), were used to characterize the energetic particle distributions originating from plastic foil targets of varying thickness. Both electron and proton spectra were measured successfully, as well as the consistent absolute numbers of accelerated particles.

With input based on actual laser performance and configuration, the researchers performed hydrodynamic and kinetic simulations to reproduce the observations. The simulations revealed the importance of energetic electron production in the extended low-density preplasma at the irradiated target surface. In addition, simulated electron and proton spectra agreed well with the experimental results.

“Optimization of target and laser characteristics will be performed to increase the energy of accelerated ions and reduce the energy dispersion for future applications,” said Raffestin.

Source: “Enhanced ion acceleration using the high-energy petawatt PETAL laser,” by D. Raffestin, L. Lecherbourg, I. Lantuejoul, B. Vauzour, P. E. Masson-Laborde, X. Davoine, N. Blanchot, J. L. Dubois, X. Vaisseau, E. D’Humières, L. Gremillet, A. Duval, Ch. Reverdin, B. Rossé, G. Boutoux, J. E. Ducret, Ch. Rousseaux, V. Tikhonchuk, and D. Batani, Matter and Radiation at Extremes (2021). The article can be accessed at http://doi.org/10.1063/5.0046679 .