Optimal design of a high current MEBT with chopper

Many existing and proposed projects require a certain temporal structure imposed on the beam pulse, e.g creating gaps for low-loss extraction from a circular accelerator. Usually this is achieved using chopper systems. In order to reduce the average beam power on the chopper target and simplify kicker requirements, the chopper system is located in a lower energy part of the accelerator, typically in the medium energy transport line (MEBT) between the RFQ and the linac. Many of the MEBT layouts proposed and in use, look very much alike and try to achieve a compromise between the two opposing requirements of providing strong transverse focusing and sufficiently long empty drifts for the kickers. As a result, both requirements are not fully satisfied leading to space charge induced emittance increase and very challenging technical specifications for the kicker and its power supply. These difficulties quickly increase with the beam current. We propose a different MEBT layout, which does not compromise the quality of beam transport and allows space for a kicker with any reasonable parameters. A generic design of a 5.5 m long MEBT transporting 100 mA with emittance increase of less than 5% is shown as an example.