Multistaged positron acceleration with beam driving diffraction radiation

It has been recently demonstrated that coherent transition radiation (CTR) can effectively accelerate positrons to high energy. However, the CTR field tends to diverge and weaken as it propagates in a vacuum, which adversely affects positron energy gain over long distances. Here, we propose a method for multi-staged positron acceleration relying on diffraction radiations (DRs) produced by the energetic drive electron beam passing through a series of periodic diffraction apertures (PDAs). The generated DR can pump energy into the initial CTR field, and the superposition of CTR and DR fields creates a hybrid strong accelerating field that can sustain for much longer distances. Our particle-in-cell simulations show that this combination of DR and CTR provides an acceleration gradient up to 8.7 GV/m and is capable of trapping and accelerating positrons over a few centimeters. We demonstrate that, using a 100-MeV drive electron bunch, the witness positrons can be accelerated from 2 to 137 MeV, with an energy spread of 1.7%. The energy gain is almost tripled compared to the case without the periodic apertures. This scheme can operate with electron beams that are available from laser-driven sources, thus offering an effective approach for realizing all-optical tabletop positron accelerators in the future.