A New Bunching Scheme for Increasing the LANSCE WNR Peak Beam Current

The LANSCE linac simultaneously provides both H- and H+ beams to several user facilities. The Weapons Neutron Research (WNR) user facility is configured to accept the H- beam with a typical pulse pattern of one linac micro-pulse every 1.8 microseconds. This pattern is produced through a combination of chopping and bunching in the 750 keV beam transport. One downside of the chopping process is that the majority of the beam produced by the ion source during each WNR macro- pulse is discarded. By applying a longitudinal bunching action immediately following the ion source, simulations have shown that some of this discarded beam can be used to increase the charge in these micro-pulses. Recently, we began an effort to develop this buncher by superimposing 16.77 MHz RF voltage on one of the HVDC electrodes in the 80 kV column adjacent to the source. This paper describes the beam dynamics simulations, design and implementation of the RF hardware and the results of tests performed with the system.