Development of superconducting resonators for the Argonne heavy-ion linac

Recent developments include a method for conditioning resonators which has produced a significant increase in accelerating gradient and also a design for a split-ring resonator with an optimum particle velocity of 0.16 c. Results of using a 1500 watt rf source to condition superconducting split-ring resonators are described. By repetitively pulsing for a few msec to field levels as high as an 8 MV/m effective accelerating field E/sub a/, electron loading at high field levels has been substantially reduced. After such conditioning, continuous operation at E/sub a/ > 6 MV/m, corresponding to a peak surface electric field of 30 MV/m, has been obtained. A split-ring resonator designed for an optimum particle velocity #betta# = v/c = 0.16 is also described. The 145.5 MHz resonator is contained in the same 16 inch diameter, 14 inch length housing used for the #betta# = 0.1 Argonne split-ring. In design of the split ring element, a 20% reduction in peak surface electric field has been achieved with no significant increase in surface magnetic field