Energetic Ion Beam Acceleration from High-Z Cryogenic Jets Interacting with a PW-Class Laser*

Laser-driven ion beams are highly valued in fundamental physics, cancer therapy, and materials science, due to their high directionality, peak fluxes, and MeV-scale energies. Efficient production of collimated energetic ion beams requires debris-free primary targets that can be rapidly replenished, which cryogenic jets fulfill, enabling high-repetition operation [1,2]. To generate fast, high Z ion sources, evaporating contaminant hydrocarbon layers of laser-irradiated targets is crucial to prevent preferential production of protons [3]. With their inherent purity, cryogenic jets eliminate that need, and can produce sub-micron thick samples, ideal for ion acceleration [4]. In a recent experiment at Helmholtzzentrum für Schwerionenforschung (HZRD), cylindrical (10 μm diameter) and sub-micron cryogenic jets of argon were irradiated by the DRACO PW laser (800nm, 20J, 30fs). Ion beam spectra and angular divergence were characterized using Thomson parabolas and ion imager. An electron spectrometer with transmission diagnostics monitored interaction quality. We spanned the laser intensity from 5x10¹⁹ to 5x10²¹W/cm² to explore the transition from TNSA to relativistically induced transparency regime. After presenting the first experimental findings, we will discuss the implications for future applications.

[1] J. B. Kim, et al., Review Sci. Instrum., 87, 11E328 (2016)

[2] L. Obst et al., Sci. Reports, 7, (2017)

[3] P. Martin et al, Commun. Phys 7, 3 (2024)

[4] T. Ziegler et al., Nat. Phys. (2024)