Injection Dynamics and Multiturn Charge-Exchange Injection into the Fast Cycling Synchrotron for the SNS

The Spallation Neutron Source (SNS) under construction at the Rutherford Laboratory is based on a high intensity, 800 MeV proton synchrotron, cycling at 50 Hz. An injected proton intensity of 5 × 1013 protons/pulse is obtained by injecting approximately 250 turns of negative hydrogen ions through a stripping foil in a charge-exchange injection system. The injection system is described and the results of studies on the injection dynamics are presented. The multiturn phase space stacking of the beam and the resulting proton density distributions have been studied with an aim to minimising beam instability problems in the synchrotron. With multiple traversals of the stripping foil, it is shown that obtaining high stripping efficiency with minimum scattering in energy and angle, places a severe constraint on the foil thickness in a high intensity machine. The high mean foil temperature and the thermal cycling produced by the high mean and pulsed current require the foil to be of a refractory material and the results of investigations into suitable materials are presented.