Instabilities study and implications for the RIA project

The rare isotope accelerator (RIA) requires a high power linac capable of accelerating all ions up to uranium to energies of 400 MeV/u with a beam power of 100 to 400 kW in a CW regime. One of the most challenging features of the proposed RIA driver linac is the simultaneous acceleration of different charge states in order to increase the final beam power. The acceleration in the last part of the accelerator is provided by elliptical cavities. Three geometrical β are used: 0.47, 0.61 and 0.81. To minimize the cost, one option is to reduce the number of cryostats. This implies a maximal number of cavities per cryostat. Assuming a lattice composed by one doublet and one cryostat, this option leads to an increase of the longitudinal phase advance if each cavity is used at the maximum field. The transverse phase advance, has to be set correctly in order to ensure stable motion. This report aims to evaluate the sensitivity to instabilities induced by the transverse to longitudinal coupling in the elliptical cavities of the RIA linac for an 88⁺ uranium beam.