A 145 MHz niobium split-ring resonator for particle velocities from 0.12 to 0.23 c

A niobium split ring resonator has been designed with an optimum particle velocity β = v/c = 0.16. This type of resonator will be used to extend the Argonne superconducting heavy-ion linac. The peak surface electric field in the resonator is 3.9 times the effective accelerating field, a value 20% lower than for previously developed split-ring resonators. A prototype niobium resonator has been completed. Results of performance tests are discussed.