Advanced Photon Source booster synchrotron subharmonic rf capture design

Recent efforts at the APS have focused on improving overall injector system reliability and availability for top-up mode storage ring operation. One proposal being considered is to implement direct injection of the beam from the linac into the booster synchrotron, thereby bypassing the particle accumulator ring (PAR). Efficient capture of the long linac macropulse (>/spl sim/ 10 ns) can be accomplished by adding an additional rf system in the booster at an appropriate subharmonic of the 352-MHz rf system. The subharmonic system is used during injection up to approximately 3 GeV, then the 352-MHz system is turned on to accelerate the beam to 7 GeV. The particle tracking program elegant is used to simulate rf and magnet ramping, beam loading, and HOM effects at up to 10-nC beam charge. Issues addressed in this design are efficient beam capture and acceleration to 7 GeV while maintaining adjacent bunch purity. Tolerances on various rf system parameters are presented in order to maintain bunch purity to better than 1 part in 100,000.