Development of collimator jaw of J-PARC MR

The jaw of beam collimator in J-PARC MR has been developed and renovated. At first, scatterer-catcher type collimator-system are used. The acceptable loss power was only 450 W. The jaw material was tantalum. Then the scatterer was changed to 2 compact collimators in 2012 because of the more acceptable 2 kW beam loss. In this system, the jaw plate was changed to L-shape block. In 2013, the collimator-2 are thrown away and 4 new collimators were installed. Then total 7 collimators and 3.5 kW beam loss was acceptable. The material of jaw was changed to tungsten. The surface of jaw is tilted in parallel to a beam envelope. In 2015, jaw duct and double-bellows ducts were separated with the flanges for simplicity. In future, a renaissance-scatterer will be installed to upper area of the first collimator. (author)