Target pre-heating has proven to be beneficial for laser-driven heavy-ion acceleration. As it allows to remove omnipresent carbohydrate surface contaminants, heating can affect the cutoff energy and increase the efficient acceleration of heavy ions as, e.g., required for the novel fission-fusion nuclear reaction scheme where kinetic energies of fissile species around 7 MeV/u are targeted. At the Centre for Advanced Laser Applications in Garching we use a 3W Nd:YAG cw laser to heat the (in our case gold) target foil in order to investigate the dependency of efficient gold ion acceleration on heating parameters. For real-time assessment of the surface temperature the thermal spectrum is measured with a NIR spectrometer to which Planck’s law is fitted.
The proposed ‘fission-fusion’ reaction mechanism aims at investigating the rapid neutron-capture process, contributing to the formation of heavy elements, by using laser-accelerated thorium ions in a sandwich target configuration [1]. In a first step, the efficient acceleration of gold ions is investigated, as recently achieved in our measurement at the PHELIX laser with 500 fs long pulses [2]. In this experiment, for the first time, the laser-based acceleration of gold ions above 7 MeV/u was demonstrated. Additionally, individual gold charge states were resolved with unprecedent resolution. This allowed to investigate the role of collisional ionization using a developmental branch of the particle-in-cell simulation code EPOCH [3], showing a much better agreement of the simulated charge state distributions with the experimentally measured ones than when only considering field ionization. This work is continued at the Centre for Advanced Laser Applications (CALA), using the ATLAS 3000 laser (800 nm central wavelength, 25 fs pulse length).
[1] D. Habs et al., Appl. Phys. B 103, 471-484 (2011)
[2] F.H. Lindner et al., Sci. Rep. 12, 4784 (2022)
[3] M. Afshari et al., Sci. Rep. 12, 18260 (2022)
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