Macro-particle simulation study on transverse halo collimator for J-PARC linac

To realize the transverse emittance required for the ring injection, a transverse halo collimation system of the charge-exchange type has been developed for J-PARC (Japan Proton Accelerator Research Complex) linac. In this type of collimation system, negative hydrogen ions constituting a tail portion are charge-exchanged to protons with thin foil collimators. Then, the generated protons are separated by a bending magnet to be delivered to a dedicated beam dump. Because a two-species beam is transported along the collimation system, a special care is to be taken to avoid the uncontrolled beam loss along the beam transport. To this end, it is of practical importance to develop an accurate numerical model that has the capability of both particle tracking with space-charge effects and modeling of scattering at the charge-exchange foil. In this paper, a numerical model is developed for the collimation system using a three-dimensional particle-in-cell code, IMPACT, and a Monte-Carlo simulation tool kit, GEANT. Uncontrolled beam loss along the collimation system has been evaluated with this model, and the optimum foil thickness has been determined for the collimation system.