Modeling and Measurements of the DUVFEL Photoinjector Cavity RF Properties

The 1.6 cell S-band photoinjector cavity has been in operation at the DUVFEL at BNL for the past year. The initial beam measurements indicated a higher than expected emittance and beam divergence at the exit of the gun field. The imbalance in the two cells was suspected, but lack of field probes in the cavity prohibited direct confirmation. A detailed SUPERFISH model was constructed of the cavity assembly. The field balance as a function of cathode plate and tuner position was determined using the model. A series of calibrated measurements of both the cavity RF properties and the delivered RF power was undertaken. Electron beam properties were also measured as a function of cavity tune. Significant improvements in beam quality were achieved. The simulations and measurements are presented.