A variable field phase-shifter for recirculating proton linacs

The recirculating superconducting proton linac that has a potential to substantially save accelerator cost was recently proposed. It consists of three sections to accelerate the continues-wave (CW) beam to multiple GeVs. In the first section, the beam passes the linac two times. In the second and third sections, the beam goes through the linac four and six times. A phase-shifter is needed to meet the synchronous acceleration condition for multi-pass acceleration using the same RF cavity due to the phase slippage of the proton beam. Here we present the design of a variable field rectangular bend phase-shifter in which the beam goes to a different path in each pass inside the magnet to meet the synchronous condition.