Photo-injector Specifications

The photo-injector is based on the Gun-IV design that was developed as part of the ATF photo-injector research program. It is a 1.6 cell RF structure where the back wall of the partial cell is the photocathode. The RF power of up to 10 MW provided by the same klystron that drives the first two linac sections. Because it is a standing wave structure substantial power can be reflected back to the klystron so an RF isolator is used to improve the performance and stability of the system. Accelerating field gradients of as much as 100 MV/m can be achieved.

Emittance compensation is provided through the use of a solenoid that focuses the photo-beam to the entrance of the first linac tank. A pair of steering coils resides inside of the solenoid to correct steering errors. The 266 nm light for stimulating emission from the photo-injector is introduced with a mirror located in a vacuum cross just down stream of the solenoid to provide near normal incidence illumination of the photocathode. A complementary mirror provides a means to extract light reflected from the cathode, and can be used for viewing the laser spot on the cathode. Another cross further down stream houses diagnostics for measuring the electron beam size, position and charge.