Experimental set-up for cell irradiation at L2A2

Ultra-short and ultra-intense pulsed lasers (> 1 J, < 100 fs) allow us to accelerate short bunches of protons and ions to MeV-range energies. Our aim is to design and build an experimental setup in the L2A2 laboratory, at the University of Santiago de Compostela, for the study of DNA double-strand breaks caused by laser-driven accelerated protons and carbon ions on human cancer cells cultures. The laser device at L2A2 delivers 1.2 J pulses at a rate of 10 Hz and peak power of 50 TW. The corresponding focused intensity is sufficient to accelerate protons up to 5-10 MeV through the Target Normal Sheath Acceleration mechanism (TNSA). In our setup, a tabletop Ti:Sapphire laser emits pulses focused onto a wheel that provides a fresh target for every shot. The beam of accelerated protons/ions passes through a pinhole followed by a sequence of permanent magnets that generate a configuration of antiparallel magnetic fields with two main purposes: On the one hand, the magnetic fields completely sweep away the unwanted bunch of electrons. Also, they bend the trajectories of the protons/ions and separate them from the photon beam that is also generated in the process. On the other hand, the magnetic fields act as an energy separator, as they bend the trajectories of the protons/ions depending on their energy. This entire setup is located inside a vacuum chamber. The proton/ion beam leaves the chamber through a thin foil of Kapton (polyimide) and finally reaches the cell culture outside the vacuum system. A major challenge of this project is the precise measurement of the dose deposited by the laser-driven beams. For significant doses (up to 5 Gy), several shots may have to be accumulated. The experiment is under construction and it is planned to be running in 2021. Laser-driven ion acceleration is suggested to be a good candidate for compact and cost-saving alternative hadrontherapy techniques in the future.