A Field Symmetrized Racetrack Cavity Photoinjector for a 17 Gigahertz Electron Linear Accelerator

151 A Field Symmetrized Racetrack Cavity Photoinjector for a 17 Gigahertz Electron Linear Accelerator--Haimson Research Corporation, 3350 Scott Boulevard, Building 60, Santa Clara, CA 95054-3104; (408) 988-6007 Dr. Jacob Haimson, Principal Investigator Ms. Beverly Mecklenburg, Business Official DOE Grant No. DE-FG03-97ER82389 Amount: $74,349 Theoretical investigations and ongoing experiments with laser driven RF guns at laboratories around the world have confirmed that photoinjectors have the potential for providing ever increasing values of beam brightness to satisfy the stringent demands of high current and low beam emittance (divergence) for future linear collider and free electron laser applications. Existing photoinjectors have undesirable asymmetric field distributions, caused by the input power coupling aperture in the side wall of the cavity. These field asymmetries contribute to beam emittance growth during the RF acceleration process, thus preventing the full potential of these electron sources from being attained. The use of diametrically opposed coupling apertures in the side wall of a traditionally shaped cylindrical cavity can provide bipolar field symmetry, but this introduces quadropolar field asymmetries and also causes an enhancement of the electric field gradient on the cavity end wall surfaces. In Phase I, a novel racetrack shaped, dual feed coupling cavity, having inherent characteristics that will prevent the above field asymmetries and gradient enhancement, will be investigated and incorporated into the design of a highly field symmetrized multicell structure for a 17 gigahertz high brightness photoinjector. For transmission and control of the required microwave input power, a high power rectangular waveguide system will also be designed. In Phase II, the new photoinjector system and waveguide network will be fabricated and interfaced with an existing high peak power klystron and a short pulse laser so that beam evaluation experiments using a high gradient linear accelerator can be performed at the Massachusetts Institute of Technology, Plasma Fusion Center. Commercial Applications and Other Benefits as described by the awardee: It is anticipated that, if successful, the Phase I and Phase II efforts will result in the fabrication and testing of a short bunch, high current, low emittance, 17 gigahertz photoinjector suitable for advance accelerator and free electron laser research applications.