CW SRF Gun generating beam parameters sufficient for CW hard-X-ray FEL

TL;DR

This paper demonstrates that a 10-year-old SRF gun can produce continuous-wave electron beams with parameters suitable for hard X-ray free-electron lasers, surpassing previous benchmarks using existing technology.

Contribution

It introduces an alternative method for generating CW electron beams for hard-X-ray FELs with existing SRF technology, achieving record parameters.

Findings

Generated 100 pC, 15 ps electron bunches with low emittance.

Achieved beam parameters exceeding previous benchmarks.

Validated beam dynamics through measurements and simulations.

Abstract

SRF CW accelerator constructed for Coherent electron Cooling (CeC) Proof-of-principle (POP) experiment at Brookhaven National Laboratory has frequently demonstrated record parameters using 1.5 nC 350 ps long electron bunches, typically compressed to FWHM of 30 ps using ballistic compression. We report experimental demonstration of CW electron beam with parameters fully satisfying requirements for hard X-ray FEL and significantly exceeding those demonstrated by APEX LCLS II electron gun. This was achieved using a 10-year-old SRF gun with a modest accelerating gradient of $\sim$15 MV/m, a bunching cavity followed by ballistic compression to generate 100 pC, $\sim$15 ps FWHM electron bunches with a normalized slice emittance of $\sim$0.2 mm-mrad and a normalized projected emittance of $\sim$0.25 mm-mrad. Hence, in this paper, we present an alternative method for generating CW electron beams for hard-X-ray FELs using existing and proven accelerator technology. We present a description of the accelerator system settings, details of projected and slice emittance measurements as well as relevant beam dynamics simulations.