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In recent decades, there has been a growing interest in laser-driven ion acceleration as an alternative to conventional accelerators currently in use, thanks to a comparatively compact size and reduced costs [1]. The ultrashort, large flux ion beams produced are advantageous in several fields, such as medicine, for FLASH therapy, or proton radiography of micro and nano structures [2]. The small source size and ultra-high beam quality also allows to generate a compact neutron source using a closely coupled secondary target [1,3]. Moreover, laser-driven ion beams are also useful to replicate outer space conditions due to the broad ion spectrum, as well as the simultaneous presence of other kinds of radiation, including electrons and gamma rays [3].
At the Laser Laboratory for Acceleration and Applications (L2A2) of the University of Santiago de Compostela, a high repetition rate femtosecond laser of 45 TW is used for ion acceleration. It can deliver pulses of 1.2 J and 25 fs at 10 Hz, which are focused down to a few microns spot achieving intensities greater than 10
In addition to replacing the target at such repetition rates, a future laser-based accelerator also requires the laser system to remain stable throughout long irradiation sessions. For this reason, the laser stability has been characterised for an extended period of up to 6 hours, focusing on its energy, pointing, and wavefront. Results showed a slow variation of the laser properties, with slight energy loss, pointing drift and an introduction of astigmatism in the wavefront, with potential solutions to these issues being currently explored.
[1] A. Macchi, M. Borghesi, and M. Passoni, Reviews of Modern Physics 85.2 (2013): 751.
[2] P. Chaudhary, et al. Radiation Oncology 17.1 (2022): 1-14.
[3] H. Daido, N. Mamiko, and A. S. Pirozhkov. Reports on progress in physics 75.5 (2012): 056401.