Buncher cavity resonant at the first and second harmonic

A buncher is an RF accelerator followed by a drift space. Its purpose is to bunch the dc ion source beam into suitable bunches for acceleration in a linac. The voltage in a simple buncher is a sine wave at the linac frequency. A more elaborate wave form can result in increased capture of ion source beam. The cavities discussed here are resonant at 12.5 and 25 MHz, the first and second harmonic of the Argonne National Laboratory (ANL) low beta linac. They will support a wave form which should give improved bunching. Three designs are given to compare their relative merits