Kinking twin beams

The upgrade of the electron positron collider at SLAC (FACET II) promises to deliver dense, energetic and high-quality beams with the aim to study High Field QED (see FACET-II Science Workshop 2017).

However, at the interaction point (IP) of the collider, there are effects (disruption, kink instability) that must be accounted for and coupled with QED processes in the design of fruitful experiments. With the PIC code OSIRIS, we simulated the self-consistent beam-beam interaction dynamics including the effect of a transverse misalignment of the two colliding beams and incorporating as well the QED processes of photon emission (non-linear Compton scattering) and pair production (Breit-Wheeler).

The video shows the evolution of the positron beam (red) and the electron beam (green) density. The two beams propagate horizontally. During the beam-beam interaction time, disruption effect, QED pair production and kink unstable modes come into play all together. Each beam pinches under the action of the disruption effect and oscillates transversely due to the kink instability. Furthermore, the beam density shows ripples as a result of the stochasticity of the QED processes.

For more information, see Grismayer, T. Vranic, M., Del Gaudio, F., Carneiro, P., Martins, J. L., Fonseca, R. A., Silva, L. O., High fields computational challenges, FACET-II Science Workshop 2017 (2017), available here.