Overview of seven-unit collimator system and its operation for J-PARC main ring

The J-PARC main ring has three linear sections, and one have a beam collimator system downstream of the injection devices to localise beam losses. In September 2024, the seventh collimator unit was installed, completing an upgrade of the collimator system that has been underway since 2012. The system was changed from one that scatters and captures the beam halo to one that draws the jaw close to the beam core and directly removes its halo. This allowed a number of collimator units to be placed in a limited area. The original beam loss capacity in the collimator area was 450 W. Seven collimator units allow a beam loss of 3.5 kW. Currently, six collimator units are used to deliver 800 kW beams to neutrino experiments with losses of less than 500 W. By using seven collimator units, a beam of 1.3 MW can be delivered with a reasonable loss amount. The combination of units effectively removes the halo component of the beam and localises the beam losses. However, the direct removal method can create loss spots downstream of the collimator according to phase advance. This paper describes the operation of collimators in actual beam operation.