EXPERIMENTAL STUDY OF A 322 MHz v/c=O.28 NIOBIUM SPOKE

The Rare Isotope Accelerator (RIA) will accelerate heavy ions to >400 MeVlu using an array of superconducting cavities. A proposed linac design based on harmonics of 80.5 MHz will require six cavity types to cover the entire velocity range: three quarter wave resonators, one spoke cavity (half wave resonator), and two 6-cell elliptical cavities. A prototype 322 MHz niobium spoke with optimum velocity of 0.28~ has been fabricated. Each spoke would generate over I MV at 4 K for acceleration from v/c=0.20 to 0.40. Details of the design and experimental study are presented.