Electron beam profile imaging in the presence of coherent optical radiation effects

TL;DR

This paper investigates the challenges posed by coherent optical radiation effects on electron beam profile imaging in free-electron laser facilities and proposes methods to suppress these effects for improved diagnostics.

Contribution

It introduces analytical, numerical, and experimental methods to suppress coherent optical radiation effects in electron beam diagnostics, enhancing imaging accuracy.

Findings

Coherent optical radiation effects can be suppressed in dispersive beamlines.

Temporal separation techniques enable beam profile measurements despite coherent effects.

Analytical and simulation results confirm suppression methods' effectiveness.

Abstract

High-brightness electron beams with low energy spread at existing and future x-ray free-electron lasers are affected by various collective beam self-interactions and microbunching instabilities. The corresponding coherent optical radiation effects, e.g., coherent optical transition radiation, render electron beam profile imaging impossible and become a serious issue for all kinds of electron beam diagnostics using imaging screens. Furthermore, coherent optical radiation effects can also be related to intrinsically ultrashort electron bunches or the existence of ultrashort spikes inside the electron bunches. In this paper, we discuss methods to suppress coherent optical radiation effects both by electron beam profile imaging in dispersive beamlines and by using scintillation imaging screens in combination with separation techniques. The suppression of coherent optical emission in dispersive beamlines is shown by analytical calculations, numerical simulations, and measurements. Transverse and longitudinal electron beam profile measurements in the presence of coherent optical radiation effects in non-dispersive beamlines are demonstrated by applying a temporal separation technique.