Commissioning test of S-band klystron/photo-gun system for femto-second sub-MeV electron beam R&D

A timely stable femto-second electron beam system is being constructed for pump-probe time-resolved experiments and applications. A pulsed S-band klystron is installed and fully commissioned with 5.5 MW peak power in a 2.5 μs pulse length and 1 Hz repetition rate. A single-cell RF photo-gun is designed to produce with 0.16 - 1.6 pC electron bunches in a photo-emission mode within a 600 fs ∓ 3 ps at 0.5 - 1 MeV. The measured RF system jitters are within ± 1 % in magnitude and ± 0.2° in phase, which would induce 3.4 keV and 0.25 keV of ΔE
_g
, corresponding to 80 fs and 5 fs of Δt
_e
, respectively. The beam brightness could be improved by replacing a conventional photo-cathode with field emission array or carbon nanotube tips as they limit the emission area, while providing high current emission. PIC simulations indicate that our designed bunch compressor reduces the TOA-jitter by about an order of magnitude. The transport and focusing optics of the designed beamline with the bunch compressor enables an energy spread within 10
^-4
and a bunch length (electron probe) within > 50 - 100 fs.