  For development of compact ultrafast electron source system, we are currently
designing a short-pulse RF-gun with RF focusing structure by means of a series
of comprehensive modeling analysis processes. EM design of a 2.5 cell resonant
cavity with input coupler, acceleration dynamics of photo-emitted electron
bunch, EM design of RF-lens with input coupler, and phasespace analysis of
focused electron bunch are systematically examined with multi-physics
simulators. All the features of the 2.856 GHz cavity geometry were precisely
engineered for acceleration energies ranging from 100 keV to 500 keV (safety
limited) to be powered by our 5 MW S-band klystron. The klystron (Thales
TH2163) and modulator system (ScandiNova K1 turnkey system) were successfully
installed and tested. Performance tests of the klystron system show peak output
power > 5 MW, as per operation specifications. At the quasi-relativistic
energies, the electron source is capable of generating 100fC -- 1 pC electron
bunch with pulse duration close to 30 fs -- 1 ps and transverse size of a few
hundred microns. PIC simulations have shown that the electron bunch undergoes
fast RF acceleration, rapidly reaching the desired energies, which can be
controlled by tuning RF injection phase and input driving power. It has been
shown that it is possible to also focus/compress the bunch longitudinally using
a RF-lens, which would allow us to control the temporal resolution of the
system as well. While our primary analysis has been performed on a 2.5 cell
design, we are also looking into half-cell (single cavity) design that is
expected to provide the same range of beam energy with a simple configuration.
