Beam extraction and dark current study of a C-band RF photo gun

C-band RF photo gun is being developed worldwide for better electron bunch emittance, aiming to be used in advanced light sources such as diffraction-limited storage rings and free electron lasers. Initial beam tests of a 3.6-cell C-band RF photo gun achieved 6.6 MeV beam energy at 137 MV/m cathode gradient were conducted, along with high dark current; Surface checks revealed electron damage on cathodes and disk apertures after these tests. To understand and suppress the dark current, surface cleaning methods and preliminary numerical simulations have also been conducted, and the results are discussed.