Realization of an X-Band RF System for LCLs

A single X-band (11.424 GHz) accelerating structure is to be incorporated in the LINAC Coherent Light Source (LCLS) design to linearize the energy-time correlation (or gradient) across each bunch; features which originate in the preceding accelerating structures (L0 and L1) [1]. This harmonic RF system will operate near the negative RF crest to decelerate the beam, reducing these non-linear components of the correlation, providing a more efficient compression in the downstream bunch compressor chicanes (BC1 and BC2). These non-linear correlation components, if allowed to grow, would lead to Coherent Synchrotron Radiation (CSR) instabilities in the chicanes, effectively destroying the coherence of the photon radiation in the main LCLS undulator. The many years devoted at SLAC in the development of X-band RF components for the NLC/JLC linear collider project [2], has enabled the technical and financial realization of such an RF system for LCLS. This paper details the requirements for the X-band system and the proposed scheme planned for achieving those requirements.