Efficient bremsstrahlung source of positrons based on wake-accelerated electrons

Abstract: The growing interest in producing high-current beams of electron–positron pairs using lasers motivates the use of ever more high-power laser systems and the forecasting of the possibilities of future projects in this regard, such as the XCELS facility, which can provide a breakthrough in creating a record high-power source of positrons using laser-accelerated electron beams. The end-to-end numerical simulation of the acceleration of an electron bunch by a high-power XCELS radiation pulse and the generation of a positron beam by it in a converter target are substantiated using the particle-in-cell (PIC) and Monte Carlo (GEANT4) methods. The high efficiency of obtaining a record number of positrons is due to the use of the regime of relativistic self-trapping of a laser pulse for the wake acceleration of electrons, which leads to the achievement of the maximum charge of electrons with an energy of multi-MeV and to the maximum conversion coefficient of laser energy in targets of near-critical density. The possibility of a record high yield of positrons with an energy per shot at a MeV level in their classical (i.e., bremsstrahlung) production scheme is demonstrated in comparison with the yield achieved today for modern lasers or predicted for existing laser projects of the future. In this case, we are talking about the possibility of using the XCELS facility to generate a maximum number of generated positrons, ∼10¹² , which is many orders of magnitude higher than the positron yield achieved in the projects under consideration.

Keywords: positrons, electron beam, wake acceleration, XCELS laser facility.