In-beam SNS ring collimation optimisation

Hands-on maintenance of the Spallation Neutron Source (SNS) Accumulator Ring requires an uncontrolled beam loss of less than 1 nA/m. A collimator system will be used to obtain this low uncontrolled beam loss. Some beam dynamics questions related to the collimators have been studied. Various factors are optimised with the given SNS ring lattice such as collimating tube length, location, number of collimators, aperture size of primary collimators and secondary collimators, and collimator material. The beam dynamics studies indicate that movable shielding may be necessary for a few hot places downstream of the primary collimators and also that secondary collimators could be designed according to their significantly less activation. These simulations indicate that with proper collimation the uncontrolled beam loss requirements of the SNS accumulator ring may be achievable