Ultra-short pulse source of ionizing radiation with a dose rate of Gy/ps based on direct laser acceleration of electrons for studying the FLASH effect

Results of the pilot experiment on the ultra-intense irradiation of the water phantom and various biological media with laser-driven beams of relativistic electrons in context of the FLASH effect are presented. Directed high-current beams of MeV electrons were generated by the interaction of sub-ps high-energy PHELIX laser pulses with low-density polymer foam, which was converted into a plasma of near-critical density by an additional nanosecond laser pulse. The combination of 20–50 Gy of ionizing radiation delivered by the relativistic electron beam in a single laser shot and the world's highest dose rate of 70 Gy/ps makes this source unique for studying the FLASH effect and for applications. The picosecond duration of the electron beam allows the separation of the process of ultrafast (instantaneous) oxygen ionization and the subsequent chemical reactions. In each laser shot, a sudden drop in oxygen saturation as a function of the delivered dose was measured in water and biological media. The dependence obtained is consistent with the results of the Monte Carlo simulation.