Analysis of photoinjector transverse phase space in action and phase coordinates

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