Bunching Characteristics of a Buncher Using Helical Resonators

A RF Buncher consistirng of two coupled Helices tuned to 28.4 MHZ was tested on the beam line of a 400 KV DC injector. Bunched waveforms versus RF power input were measured and analysed. With 8.4 W power input the proton beam was compressed to 1 ns (FWHM) bursts. The beam pulse splitted into double peaks at a higher power level depending on the initial energy dispersion. Both peak separation and the pulse height changed remarkably with increasing power input, and the overlapping of peaks in neighbouring cycles occured alternately. By making use of phase diagram in time-energy space a simple formalism is presented for the analysis of the bunching characteristics. Results obtained are well consistnet with the experiment. The effect of the quadrupole lens on bunched waveform was also observed and discussed.