Efficient Bremsstrahlung Positron Source Based on Wakefield-Accelerated Electrons

Abstract

A growing interest in obtaining 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 positron source using laser-accelerated electron beams. For the substantiation of the latter, use is made of the end-to-end numerical simulation of the electron bunch acceleration by a high-power XCELS radiation pulse and the positron beam generation in a converter target 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 wakefield acceleration of electrons, which leads to the achievement of a maximum charge of electrons with an energy of multi-MeV and to a maximum conversion coefficient of laser energy in near-critical density targets. A possibility of a record-high yield of positrons with an energy per shot at a MeV level in their classical (i.e., bremsstrahlung) generation scheme is demonstrated in comparison with the yield achieved today for modern lasers or predicted for existing future laser projects. Thus, the case in point is 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.