Microwave measurements of the BNL/SLAC/UCLA 1.6 cell photocathode RF gun

The longitudinal accelerating field E/sub z/ has been measured as a function of azimuthal angle in the full cell of the cold test model for the 1.6 cell BNL/SLAC/UCLA 3 S-band RF gun using a needle rotation/frequency perturbation technique. These measurements were conducted before and after symmetrizing the full cell with a vacuum pump out port and an adjustable short. Two different waveguide to full cell coupling schemes were studied. The dipole mode of the full cell is an order of magnitude less severe before symmetrization for the /spl theta/-coupling scheme. The multi-pole contribution to the longitudinal field asymmetry are calculated using standard Fourier series techniques. The Panofsky-Wenzel theorem is used in estimating the transverse emittance due to the multipole components of E/sub z/.