Generalized Superradiance in the Ion Channel Laser*

Radiation emission plasmas is often a result of collective effects associated with the dynamics of large numbers of relativistic charged particles. The Particle-In-Cell scheme is commonly used to model their motion but may fail to capture the corresponding ultra-high radiation frequencies. The Radiation Diagnostic for OSIRIS (RaDiO) can retrieve the full EM field structure of the emitted radiation in OSIRIS PIC simulations. These codes can run reliably with a high level of efficiency in the largest CPU-based supercomputers, but the radiation algorithm has been recently adapted to the GPU architecture.

In this work, we take advantage of the latest developments in RaDiO to generalize the Ion Channel Laser concept towards superradiant Betatron emission through Generalized Superradiance. This scheme allows arbitrarily long particle beams to radiate coherently at wavelengths much smaller than the particle beam size, exploiting optical shocks coming from superluminal beam structures directed at the Cherenkov angle of structures' the phase speed. We show that by resonantly combining betatron oscillations with the effect of a low frequency laser pulse, an electron beam acquires a modulation with a superluminal phase-like velocity, and explore the necessary conditions to obtain such a modulation. The generalized ion channel laser concept can then be seeded by traditional infra-red laser pulses, and lead to temporally coherent radiation that can extend all the way up to x-ray frequencies.