High-power linac for a US Spallation-Neutron Source

We present the status of the high-power linac-design studies for a proposed National Spallation Neutron Source (NSNS), based on a linac/accumulator-ring accelerator system. The overall project is a collaboration involving five national laboratories. The Oak Ridge National Laboratory will be responsible for the target, facilities, and the conceptual design; Brookhaven National Laboratory will be responsible for the ring; Lawrence Berkeley National Laboratory will be responsible for the injector, including the RFQ and a low-energy chopper located in front of the RFQ; Los Alamos National Laboratory will be responsible for the main linac, and the Argonne National Laboratory will be responsible for the instrumentation. The facility will be built at Oak Ridge. In the first phase, the dual-frequency linac with frequencies 402.5 and 805 MHz must deliver to the accumulator ring an H- beam with nominal energy near 1 GeV, with a pulse length of about 1 ms at a repetition rate of 60 Hz, and with a nominal average beam power of at least 1 MW. The linac can be upgraded by a factor of four in beam power by increasing the de-injector current, and by funneling the beams from two 402.5-MHz low-energy linacs into the 805-MHz high-energy linac. Requirements for low beam loss in both the linac and the ring have important implications for the linac design, including the requirement to provide efficient beam chopping, which is necessary to provide low-loss extraction for the ring. The linac-design options and initial parameters will be presented, together with initial beam-dynamics simulation results.