Testing and Implementation Progress on the Advanced Photon Source (APS)   Linear Accelerator (Linac) High-Power S-band Switching System
  An S-band linear accelerator is the source of particles and the front end of the Advanced Photon Source injector. In addition, it supports a low-energy undulator test line (LEUTL) and drives a free-electron laser (FEL). A waveguide-switching and distribution system is now under construction. The system configuration was revised to be consistent with the recent change to electron-only operation. There are now six modulator-klystron subsystems, two of which are being configured to act as hot spares for two S-band transmitters each, so that no single failure will prevent injector operation. The two subsystems are also used to support additional LEUTL capabilities and off-line testing. Design considerations for the waveguide-switching subsystem, topology selection, control and protection provisions, high-power test results, and current status are described 
A.E. Grelick, N. Arnold, S. Berg, D. Dohan, G. Goeppner, Y.W. Kang, A.   Nassiri, S. Pasky, G. Pile, T. Smith, S.J. Stein