Analysis of photoinjector transverse phase space in action and phase coordinates

TL;DR

This paper analyzes the transverse phase space of photoinjectors in action and phase coordinates, providing a more intuitive method for calculating beam core brightness crucial for XFEL performance.

Contribution

It introduces a novel analysis of phase space in action and phase coordinates for both models and experiments, enhancing understanding of beam brightness.

Findings

Provides a new framework for phase space analysis

Improves accuracy of beam core brightness calculation

Highlights sensitivity of emittance to low intensity tails

Abstract

Photoinjectors are the main high brightness electron sources for X-ray free electron lasers (XFEL). Photoinjector emittance reduction is one of the key knobs for improving XFEL lasing, so precise emittance measurement is critical. It's well known that rms emittance is very sensitive to low intensity tails of particle distributions in the phase space, whose measurement depend on the signal to noise ratio (SNR) and image processing procedures. Such sensitivities make the interpretations of beam transverse brightness challenging, leading to different emittance definitions to reduce the impact of tail particles. In this paper, transverse phase space is analyzed in action and phase coordinates for both analytical models and experiments, which give a more intuitive way to calculate the beam core brightness.