  Superconducting radio-frequency (SRF) guns are promising candidates to
deliver high brightness continuous-wave (CW) electron beams for new generations
of coherent linac light sources, ultrafast electron diffractions, MeV pulsed
beam applications, etc. To solve the compatibility problem of semiconductor
photocathodes, a hybrid gun combining a direct-current gap and an SRF cavity
has been developed. The gun, employing K2CsSb photocathodes driven by a green
laser, has been brought into stable CW operation with a dark current below 100
pA, delivering electron beams at an energy gain of 2.4 MeV, an electron bunch
charge of 100 pC, and a repetition rate of 1 MHz. A normalized beam emittance
of 0.54 mm-mrad has been achieved at the bunch charge of 100 pC and peak
current of about 6 A. CW operation at 81.25 MHz repetition rate has also been
tested with the maximum average beam current reaching 3 mA.
