Microwave and beam optics design features of a preinjector linac for a synchrotron radiation source

A discussion is presented of the microwave and beam optics parameters of a chopper-prebuncher injection system and a 55-MeV, 2998-MHz, 2.8-m-long accelerator waveguide assembly designed to produce inherently sharp beam energy spectra (0.5%) over a range of booster injection pulse periods from approximately 200 to 1.5 ns. The DC-biased 2998-MHz chopper and prebuncher system is designed to inject into the accelerator waveguide sharply defined bunches with essentially all of the charge contained in less than 15 degrees of longitudinal phase space and with a narrow spread of electron velocities. Also, the single-section, nonuniform impedance waveguide structure is designed to prevent energy spectrum broadening (typically from asymptotic off-crest bunch location during acceleration) by combining correlated energy-phase orbits with a nodal detuned circuit arranged to give two opposing over-the-crest phase drifts when the linac is operated at precisely six times the booster frequency.<>