Simulation Study of Positron Beam Generation via Irradiating an Ultra-Intense Laser on a Hollow Target

By simulation with the relativistic PIC code EPOCH, it is found that a hollow target ismore beneficial than a plane one for the collimation and compression of the positrons. Irradiating anultra-intense laser (4×1023 W/cm2) on a hollow target, 8.74×1015 positrons are generated. Due tothe focusing effect of the transverse electric field formed in the hollow wall, the divergence angle isaround 21° , while the maximum density of the beam is 4.77×1021 cm-3. When the laser intensity is doubled, both the yield (5.31 ×1016) and the maximum density (1.57 ×1022 cm-3) are greatly increased while the beam divergence gets even smaller (15.7 °).