Speaker
Description
The interaction of electromagnetic radiation with the density gradients of a beam-driven plasma wakefield can lead to significant frequency upshifting — a process known as photon acceleration. Simulations of this phenomenon are computationally expensive due to the strict resolution requirements imposed by the CFL condition. To mitigate this, we introduce a photon kinetic model to the particle-in-cell (PIC) code OSIRIS, in which a laser pulse is represented as a distribution of macro-particles in phase space evolving according to the photon ray equations. This kinetic description replaces the full electromagnetic solve for the high-frequency laser pulse, therefore reducing the computational cost while retaining the relevant physics of photon acceleration. We validate this model by comparing the evolving phase space distribution to the Wigner transform of the electromagnetic field from a full PIC simulation. We also present a feedback model in which the photon distribution modifies the plasma electron distribution through the ponderomotive force, allowing for a fully self-consistent simulation of the laser-plasma interaction. We apply this model to study photon acceleration in wakefields driven by 400 GeV proton beams, similar to those in the AWAKE experiment.
| Working group | WG6 |
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