Superconducting cavities are widely used for acceleration of light and heavy-ion beams. A new major application of SC cavities is the Rare-Isotope Accelerator (RIA) Project which includes a cw 1.4 GV driver linac and a 123 MV post-accelerator both based on SC cavities operating at frequencies from 48 MHz to 805 MHz. Several new conceptual solutions in physics design of heavy-ion SC linacs have been developed recently. Particularly, the concept of multiple charge state beam acceleration in SC linacs was tested and will be used in the RIA driver linac to increase available accelerated beam power. A detailed design has been developed for the focusing-accelerating lattice of the RIA linacs. 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. Comparison of beam dynamics performance in the high-beta section of the RIA driver linac has been done for two types of accelerating structures: elliptical cavities as in the baseline proposal and triple-spoke cavities.

A post-accelerator for rare isotopes (RIB linac) must produce high-quality beams of radioactive ions over the full mass range, including uranium, at energies above the coulomb barrier. To provide the highest possible efficiency for rare isotopes with masses from 6 to 240, the linac will accept all ions in the 1+ charge state. A high resolution separator for purifying beams at the isobaric level precedes the RIB linac. Charge stripping in the linac takes place at two stages: helium gas stripping at energies of 8 keV/u (light ions) and 20 keV/u (heavy ions), and an additional foil stripping at ~680-1700 keV/u for the heavier ions. A multiple-charge-state mode of operation can be used after the second stripper to produce higher intensities of accelerated radioactive beams.

The front ends of both the driver linac and the post-accelerator will utilize room temperature accelerating structures. The most suitable initial acceleration of heavy ion beams uses conventional copper structures such as Radio Frequency Quadrupole accelerator or its modifications. Progress in R&D and prototyping work related to the development of several types of RFQs operating at 12 MHz, 24 MHz and 57.5 MHz will be discussed.


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