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

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.

Figures (7)

• Figure 1: CeC SRF CW gun and cathode transfer system.
• Figure 2: CeC SRF CW gun and cathode delivery system.
• Figure 3: Measured horizontal and vertical projected emittances for electron bunches with different total charge (6.25-100 pC). This is shown for three combinations of iris diameter on cathode and gun solenoid current, which give the best measured emittances at YAG 1 location.
• Figure 4: Measured horizontal and vertical projected emittances for 25, 50 and 100 pC electron bunches using Triplet quadrupoles (Q1, Q2 and Q3) and Triplet PM in Dogleg section.
• Figure 5: CeC time-resolved diagnostics beamline (TRDBL).