Hettel, R.O.
(Rowan O. Hettel)

MOPOS64 Emittance and Quantum Efficiency Measurements from a 1.6 cell S-band Photocathode RF Gun with Mg Cathode
John F. Schmerge, John M. Castro, D. H. Dowell, Steve M. Gierman (SLAC/LCLS, Menlo Park, California), Jym E. Clendenin (SLAC/AD, Menlo Park, California), Rowan O. Hettel (SLAC/SSRL, Menlo Park, California)

Previously we had shown transverse slice and longitudinal emittance measurements using a 1.6 cell S-band rf gun with a Cu cathode [1]. Slice emittances at low charge (15 pC) set an upper limit of 0.6 microns per mm radius. Previous measurements were limited to a maximum of 600 pC total charge due to the relatively low quantum efficiency (5 10-5) of the copper cathodes. In order to increase the available charge to the nC level, we have installed a Mg cathode. The lower work function of Mg compared to Cu increases the quantum efficiency for a fixed laser wavelength but also potentially increases the thermal emittance. Emittance measurements with the Mg cathode will be presented and compared with previous Cu cathode measurements.