Efficient linac-based production of slow positrons

Abstract

A novel technique for efficient production of slow positrons is proposed. It is based on the trapping of electroproduced relativistic positrons in a high field magnetic bottle. By introducing a small drift motion the emitted positrons are prevented from re-striking the production target and they undergo extended radiative cooling. By adding high voltage electrostatic trapping the cooling can proceed down to very small transverse momenta. In the simplest version of the method the wide distribution of final longitudinal momenta is conserved until a dedicated extraction procedure converts the trapped positrons into a quasi-continuous beam of very low energy. What comes out is a slow positron beam with the same quality as that obtained with the standard moderation scheme. The conversion efficiency is around 0.01 e +/e − and beam intensities exceeding 10 11 e +/s can be obtained with a moderate linac average current.