Geometry Optimization of DC/RF Photoelectron Gun

High gradient pre-acceleration of photoelectron in a pulsed high voltage, dc gap and its subsequent injection into an rf gun is a promising method to improve electron beam emittance in rf accelerators. Simulation work has been performed in order to improve beam properties by optimizing the geometric shapes of a cylindrically symmetric dc/rf gun. Variations were made on cathode and anode shapes, dc gap distance and anode iris length. Significant improvement on the normalized transverse emittance Xn (<<1 mm·mrad), was obtained, as compared to an rf gun only or dc guns with flat cathode, after the gun geometry was optimized.