A Study of Beam Chopping Options for the ATLAS Positive Ion Linac

Unbunched beam components from the injection beam bunching system must be removed prior to acceleration in the ATLAS Positive Ion Injector Linac(PII). A sine-wave chopper has been used for this purpose up to now. Such a device can have a significant detrimental effect on the longitudinal and transverse beam emittance of heavy-ion beams which can be sufficiently severe to limit the overall beam quality from the ATLAS accelerator. A study of the optimum chopper configuration and chopper type was undertaken as part of a new ion source project for ATLAS. A transmission-line chopper and a two-harmonic chopper were investigated as alternatives to the conventional sine-wave chopper. This paper reports the results of that investigation and discusses the design of the selected transmission-line chopper