DESIGN FEATURES OF HIGH-INTENSITY MEDIUM-ENERGY

The proposed Rare Isotope Accelerator (RIA) requires the construction of a cw 1.4 GV superconducting (SC) linac that is capable of producing 400 kW beams of all ions from protons at 900 MeV to uranium at 400 MeV/u. The design of such a linac was outlined at the previous Linac conference. This linac will accelerate multiple-charge-states (multi-q) of the heaviest ion beams, for which the beam current is limited by ion-source performance. The linac consists of two different types of accelerating and focusing lattice: for uranium below ~85 MeV/u the focusing is provided by SC solenoids installed in cryostats with the SC resonators while in the high-beta section the focusing elements are located outside of the cryostats. A detailed design has been developed for the focusing-accelerating lattice of the linac. Beam dynamics studies have been performed with the goal of optimization of the linac structure in order to reduce a possible effective emittance growth of the multi-q uranium beam. A wide tuning range of the accelerating and focusing fields is required for acceleration of the variety of ions with different charge-to-mass ratios to the highest possible energy in single charge state mode. The focusing must be retuned for different ion masses to avoid resonance coupling between the transverse and longitudinal motions. Any visible impact of this coupling on the formation of beam halo must be avoided due to the high beam power