RF Design for the Linac Coherent Light Source (LCLS) Injector

Abstract

The Linac Coherent Light Source (LCLS) will be the world's first x-ray free electron laser, and the successful operation of this very short-wavelength FEL will require excellent beam quality from its electron source. Therefore a critical component is the RF photocathode injector. This paper describes the design issues of the LCLS RF gun and accelerator structures. The injector consists of a 1.6 cell s-band gun followed by two 3-meter SLAC sections. The gun and the first RF section will have dual RF feeds both to eliminate transverse RF kicks and to reduce the pulsed heating of the coupling ports. In addition, the input coupler cavities will be specially shaped to greatly reduce the RF quadrupole fields. RF designs for the gun and the first accelerator section are now complete. The work includes the gun's new dual coupler and full cell shape as well as the dimensions of the L0-1 dual RF feed and coupling cell. Engineering has begun on the L0-1 structure. These and other aspects of the gun and RF structure design will be discussed.