Electron-positron QED cascades in the collision of tightly focused lepton beams

Electron-positron QED cascades are important in extreme astrophysical environments, such as pulsar magnetospheres, and are of fundamental interest in strong-field quantum electrodynamics. Recently, there has been a significant effort to study the conditions for the onset of pair cascades in the laboratory, using ultra-intense laser fields. We will present the results of QED-PIC simulations that show for the first time that QED cascades can also be studied in the head-on collision of tightly focused 10 GeV-class electron-positron beams. In the moderate disruption regime (D = 1 - 4), these beams are strongly compressed during the interaction, leading to very large field amplification that can exceed the Schwinger field by a factor $>$ 100 in the frame of the beams, and to a QED cascade that reaches a multiplicity of 10. We have derived an analytical model and show that it is able to recover the cascade rate and saturation time as a function of the beam parameters.