A retrofit/upgrade of the Stony Brook linac

We describe a project to replace the initial 16 split-loop resonators in the Stony Brook superconducting booster linac with β0=0.068 quarter wave resonators (QWRs). When completed, this retrofit will assure phase stable linac operation at output energies from 20% to as much as (for the heaviest ions) 80% higher than before. The resonator performance goal of Ea=3 MV/m at 6 W dissipation has been achieved by plating a thin lead-tin layer after tumbling the copper surface, and most of the engineering and fabrication work has been completed. Although until now multipactoring during the test runs has been intense and frequently intractable, recent experiments have demonstrated that this can be routinely eliminated by room-temperature rf ''pre-processing'' with careful control of the vacuum quality. (orig.)