Multi-objective Optimizations of a Novel Cryo-cooled DC Gun Based Ultra Fast Electron Diffraction Beamline

TL;DR

This paper uses multi-objective genetic algorithms to optimize a novel cryo-cooled DC gun for ultra-fast electron diffraction, achieving high coherence lengths and demonstrating the method's effectiveness in beamline design.

Contribution

It introduces a multi-objective genetic algorithm approach for optimizing a cryo-cooled DC gun based electron diffraction beamline, focusing on emittance and coherence length improvements.

Findings

Achieved a coherence length per rms spot size of 0.27 nm/micron at 100k electrons.

Obtained a coherence length per rms spot size of 0.1 nm/micron at 1000k electrons.

Demonstrated the viability of genetic algorithms in ultrafast electron diffraction beamline design.

Abstract

We present the results of multi-objective genetic algorithm optimizations of a potential single shot ultra fast electron diffraction beamline utilizing a 225 kV dc gun with a novel cryocooled photocathode system and buncher cavity. Optimizations of the transverse projected emittance as a function of bunch charge are presented and discussed in terms of the scaling laws derived in the charge saturation limit. Additionally, optimization of the transverse coherence length as a function of final rms bunch length at sample location have been performed for three different sample radii: 50, 100, 200 microns, for two final bunch charges: 100k and 1000k electrons. Analysis of the solutions is discussed, as are the effects of disorder induced heating. In particular, a coherence length per rms spot size of 0.27 nm/micron was obtained for a final bunch charge of 100k electrons and final rms bunch length of approximately 100 fs. For a final charge of 1000k electrons the cryogun produces a coherence length per rms spot size of 0.1 nm/micron for an rms bunch length of 100-200 fs and final spot size of 50 micron. These results demonstrate the viability of using genetic algorithms in the design and operation of ultrafast electron diffraction beamlines.