THE BULK NIOBIUM RESONATORS PROGRAM AT LNL

The encouraging results of the 160 MHz niobium quarter wave resonator (QWR) have prompted us to design, construct and test a complete set of resonators which could be used in the three consecutive sections (low-beta, intermediate and high-beta) of a superconducting heavy ion booster. They seem to be ideally suited for industrial production, since the majority of parts are identical for all three types of resonators. They are made of bulk niobium, and are heat treated under high vacuum conditions; this treatment improves the niobium RRR ratio. The direct contact with liquid helium of most niobium surfaces provides the resonator with excellent cooling. The 160 MHz resonator of beta = 0.112 planned for the intermediate-beta section of the linac gave an accelerating field of 5 MV/m at 10 W power dissipation and its low power Q was 2.4 x 10(8). The 80 MHz QWR intended for the low-beta section was constructed and heat treated; the first rf test, performed on the resonator damaged by a serious vacuum accident, looked promising, thus we have repaired the mechanical damage and the resonator will be tested again as soon as the surface treatment is performed. We have recently completed construction of the high-beta 240 MHz QWR; it will be heat treated and measured and we expect to present its rf test results in the near future.