Niobium Quarter-wave Resonator Development for the Rare Isotope Accelerator

There is a growing interest in the production of intense beams of exotic isotopes for research in nuclear physics and laboratory astrophysics [1]. The Rare Isotope Accelerator (RIA) is one such project being pursued by the nuclear physics community in the USA [2]. RIA calls for a superconducting cavity linac to accelerate the CW beam of heavy ions to ≥ 400 MeV per nucleon, with a beam power of up to 400 kW. Several types of superconducting structures are needed due to the changing velocity of the beam [3]. Design studies are in progress at Michigan State University (MSU) for a 10th-harmonic driver linac consisting of quarter-wave resonators (QWRs), half-wave resonators, and elliptical cavities [4]. Three different types of QWRs have been designed for the first segment of the driver linac. The first QWR type (optimum β ≡ βm = 0.041, 80.5 MHz) is very similar to existing QWRs in use at INFN-Legnaro (β is the beam velocity divided by the speed of light). The second (βm = 0.085, 80.5 MHz) and third (βm = 0.16, 161 MHz) types are being developed as a collaborative effort between Legnaro and MSU. This paper covers the RF design, prototyping, and preliminary RF testing of simplified versions of the βm = 0.085 and βm = 0.16 QWRs. The next step, the development of a complete βm = 0.16 cavity with an integrated helium vessel, is also underway [5].