Design of dynamic collimator for J-PARC main ring

The J-PARC main ring has a beam collimator section downstream of the injection area. The allowed beam loss is about 450 W. The beam halo generated before acceleration can be scraped by a standard collimator scheme. However the beam halo can grow during the acceleration. Such a halo may cause a serious beam loss at the extraction. A collimation during acceleration (dynamic collimator) is useful to reduce the beam loss at the extraction. We propose the dynamic collimator scheme and show the performance expected from the simulations.