Niobium cavity development for the high-energy linac of the rare isotope accelerator
The Rare Isotope Accelerator (RIA) is being designed to supply an intense beam of exotic isotopes for nuclear physics research [1]. Superconducting cavities are to be used to accelerate the CW beam of heavy ions to 400 MeV per nucleon, with a beam power of up to 400 kW. Because of the varying velocity of the ion beam along the linac, a number of different types of superconducting structures are needed. The RIA linac will accelerate heavy ions over the same velocity range as the proton linac for the Spallation Neutron Source (SNS). It was decided to use the 6-cell axisymmetric 805 MHz cavities and cryostats of SNS for the downstream portion of the RIA linac, thereby saving the non-recurring development and engineering costs. For additional cost saving, it was decided to extend the SNS multi-cell axisymmetric cavity design to lower velocity, {beta} = v/c = 0.4, using the same cryostats and RF systems. Axisymmetric cavities will thus constitute about three-quarters of RIA's total accelerating voltage, and most of that voltage will be provided by cavities already developed for SNS. The axisymmetric cavities will accelerate the RIA beam from {beta} = 0.4 to {beta} = 0.72. This velocity range can be efficiently covered with two different types of 6-cell cavities, one with a geometric {beta}, {beta}{sub g}, of 0.47, and the other with a {beta}{sub g} of 0.61. The {beta}{sub g} = 0.61 cavity will be of the existing SNS design; some {beta}{sub g} = 0.81 SNS cavities may also be desired at the end of the RIA linac for acceleration of light ions above 400 MeV per nucleon. Prototypes for both {beta}{sub g} = 0.61 and {beta}{sub g} = 0.81 have been fabricated and tested [2]. The {beta}{sub g} = 0.47 cavity is the focus of the present work. The reduction in {beta}{sub g} to 0.47 results in less favourable electromagnetic and mechanical properties, and opens up the possibility of multipacting, but several groups have already designed and prototyped cavities in this range. These efforts have been motivated mostly by the interest in high-intensity proton linacs that has arisen in the past 8 years. Single-cell cavities for {beta} = 0.47 to 0.5 have been tested at various laboratories [3, 4, 5]. The gradients and Q's reached in the single-cell tests have exceeded the design goals, and multipacting has not limited the performance. This paper will cover the design of a 6-cell {beta}{sub g} = 0.47 cavity for RIA, as well as the fabrication and RF testing of single-cell prototypes. Single-cell prototypes were chosen as a first step, as they provide a quick and inexpensive way to find out whether the desired field level and Q can be reached, and to check for problems with multipacting. An accelerating gradient of 8 MV/m was chosen as a goal for the {beta}{sub g} = 0.47 cavity.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
- Sponsoring Organization:
- USDOE Office of Energy Research (ER) (US)
- DOE Contract Number:
- AC05-84ER40150
- OSTI ID:
- 838023
- Report Number(s):
- JLAB-ACC-01-54; DOE/ER/40150-3229; PAC-2001-MPPH116; TRN: US0501189
- Resource Relation:
- Conference: PAC2001, Chicago, IL (US), 06/18/2001--06/22/2001; Other Information: PBD: 1 Aug 2001
- Country of Publication:
- United States
- Language:
- English
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