Experimental characterization of the spallation neutron source accumulator ring collimation system

The SNS ring and associated transport lines, commissioned in January 2006, are designed to accumulate and deliver up to 1.5e14, 1 GeV protons at 60 Hz to a liquid mercury target for neutron production. In order to control activation and to allow for routine hands- on maintenance of accelerator components, beam loss in most of the ring must remain below 1 W/m. For the full 1.4 MW beam, this translates to a fractional beam loss limit of 0.02%. Accomplishing this loss limit at full beam power will require successful utilization of the ring´s two- stage betatron collimation system. In this paper we present the results of initial collimation experiments. We characterize the collimation-induced beam-loss pattern and compare our results with simulations.