Radiological Issues in Laser-Matter Interactions at Under 200 PW and High Repetition Rates

摘要

The Extreme Light Infrastructure (ELI) project aims to provide laser beams up to 200 PW, with intensities in the 10~(23)-10~(25) W.cm~(-3) range. This enables ultra-relativistic laser-matter experiments, such as the development of compact particle accelerators. PIC simulations have shown that under certain conditions a directed proton beam can emerge from a thin foil at energies of several GeV per particle, with laser-to-particle energy conversion efficiencies better than 50%. At the same time electrons with energies in the 1 GeV range are scattered in arbitrary directions, including backwards and sideways. This omnidirectional source term, along with the main beam, need to be properly contained for safety and operational reasons. For that purpose the primary particle distribution given by the PIC simulations is post-processed with Geant4 and the secondary radiation and consequent material activation is determined. The relatively high repetition rates expected for ELI, up to 1 shot per minute at 100 PW and 1 kHz at 100 TW, makes the integrated material activation one of the main issues to be considered. Its implications on the facility design, personal access and operation rules are discussed.