An Ultra-Low-Emittance, L-Band, Flat-Beam PWT Photoinjector

The International Linear Collider (ILC) needs a polarized electron source capable of producing an electron beam with 85% polarization, when illuminated by a circularly polarized laser. The current design of the ILC polarized electron source is based on a DC gun and a subharmonic buncher, followed downstream by a large, expensive damping ring. This project will develop an alternative approach in which an L-band, normal-conducting, polarized electron gun of the Plane-Wave-Transformer (PWT) design is used to meet ILC specifications. In Phase I, detailed numerical simulations and tradeoff studies ¿ based on vacuum, RF, magnet, beam dynamics, thermal hydraulic, and mechanical considerations ¿ were used to identify a baseline design for the L-band, PWT photoinjector. Phase II will entail the detailed mechanical design of a 1.3 GHz, 2-cell PWT gun, followed by the fabrication and assembly of the entire system. Tests will be performed at the Fermi National Accelerator Laboratory in order to demonstrate: (1) the generation of a beam with the targeted polarization and an ultra low vertical emittance, and (2) the survivability of the GaAs photocathode needed to produce such a beam. Commercial Applications and Other Benefits as described by the awardee: The use of an L-band PWT gun as a viable electron source could potentially save ~$100M in ILC construction costs by eliminating the complicated and expensive damping ring. In other applications, the PWT gun could be used as a high brightness electron injector for linear accelerators, synchrotrons, FELs, and other light sources. In combination with a high-intensity laser, the PWT gun could serve as a Compton source for producing ultrafast, copious X-rays for applications in biotechnology, medicine, industry, and research.