Acceleration of a hollow electron beam in wakefields driven by a Laguerre–Gaussian laser pulse

Along with the rapid development of laser technology, the tabletop electron accelerator driven by laser pulses interacting with low-density plasma has achieved significant progress. Recently, a ring-shaped electron beam is widely studied for its potential applications in the collective acceleration of ions and positrons and the collimation for proton acceleration. By using three-dimensional particle-in-cell (PIC) simulations, we study that a hollow electron beam can injected and accelerated by using a Laguerre-Gaussian (LG) and ionization-induced injection in a laser wakefield accelerator. We find that both the ring size and the beam thickness of the ring-shaped oscillate during the acceleration. The beam azimuthal shape is angularly dependent and evolves during the acceleration. Nevertheless, electrons at different positions of the hollow beam have different rotation characteristics due to the two effects: the initial residual ionization momentum and the wakefield focusing force. As a result, an electron ring with non-uniform density distribution can be formed. Scaled simulations show that the ring size and the trapped electron charge of the hollow electron beam can be well controlled by tuning the laser spot size .