Slice emittance, projected emittance and properties of the FEL SASE radiation

TL;DR

This paper explores how the slice-specific properties of electron beams in FEL SASE influence the overall radiation coherence and performance, highlighting the importance of understanding individual slice characteristics.

Contribution

It introduces a detailed analysis of slice emittance and phase space properties, advancing the understanding of their impact on FEL SASE radiation coherence.

Findings

Different slices can have varying emittances and Twiss parameters.

Slice properties significantly affect the transverse coherence of the FEL output.

The concept of beam matching must consider slice heterogeneity.

Abstract

The existence of a characteristic coherence length in FEL SASE Physics determines the independent lasing of different portions, namely the slices, of the electron bunch. Each slice may be characterized by different phase space properties (not necessarily equal emittances and Twiss coefficients). This fact opens new questions on the concept of beam matching and how the various portions of the beam contribute to the performances of the output radiation, including those associated with the transverse coherence.