A chopper-buncher system for the Rehovot Pelletron

Abstract A chopper-buncher system for heavy ions has been designed, constructed and put into operation. The system was incorporated into a 14UD Pelletron electrostatic accelerator and produced beam pulses of 240 ps fwhm for 16 O ions at the target. The chopper buncher is suitable for bunching 1 H through 4 He as well as all ions from 12 C to 58 Ni. The beam is chopped by a novel deflector-redeflector chopper, which, in first order, does not increase the beam energy spread. The low energy buncher operates at 3.36 MHz basic frequency and 10.08 MHz harmonic correction and bunches the beam to under 1 ns fwhm. For higher time resolution, a 215 MHz copper cavity buncher is used. This buncher is located at the high energy side of the Pelletron before the switching magnet and it provides bunches of under 300 ps fwhm to all beam lines. An additional high energy buncher consisting of a superconducting 430 MHz niobium cavity is located on one particular beam line. This buncher, which is only 3 m distant from the target, can produce bunches of less than 100 ps fwhm when injected with bunches under 500 ps fwhm. Each of the system elements is amplitude locked and the low energy chopper-buncher elements are phase locked to the high energy buncher used. A microchannel plate timing detector is used for feedback correction of the low energy chopper-buncher phase, maintaining the proper arrival time of the beam bunches at the high energy buncher or at the target.