Slice energy spread measurement in the low energy photoinjector

TL;DR

This paper introduces a new method for accurately measuring slice energy spread in low energy photoinjectors, demonstrating significantly lower values than those observed in high energy systems, which is crucial for FEL optimization.

Contribution

A novel measurement technique for slice energy spread at low beam energies is proposed and validated, addressing discrepancies seen in high energy photoinjector measurements.

Findings

Measured slice energy spread at 20 MeV is much lower than at high energy injectors.

The new method provides more accurate and reliable measurements for low energy photoinjectors.

Results aid in better FEL optimization at low energies.

Abstract

Slice energy spread is one of the key parameters in free electron laser optimizations, but its accurate measurement is not straightforward. Two recent studies from high energy ($>$100 MeV) photoinjectors at SwissFEL and European XFEL have reported much higher slice energy spread than expected at their XFEL working points (200 - 250 pC). In this paper, a new method for measuring slice energy spread at a lower beam energy ($\sim$20 MeV) is proposed and demonstrated at the PhotoInjector Test facility at DESY Zeuthen (PITZ), and the results for 250 pC and 500 pC are much lower than those measured at high energy injectors.