  There is demand for the construction of a medium-energy ion linear
accelerator based on superconducting rf (SRF) technology. It must be capable of
producing several hundred kilowatts of CW beams ranging from protons to
uranium. A considerable amount of power is required in order to generate
intense beams of rare isotopes for subsequent acceleration. At present,
however, the beam power available for the heavier ions would be limited by ion
source performance. To overcome this limit, we have studied the possibility of
accelerating multiple-charge-state (multi-Q) beams through a linac. We show
that such operation is made feasible by the large transverse and longitudinal
acceptance which can be obtained in a linac using superconducting cavities.
Multi-Q operation provides not only a substantial increase in beam current, but
also enables the use of two strippers, thus reducing the size of linac
required. Since the superconducting (SC) linac operates in CW mode, space
charge effects are essentially eliminated except in the ECR/RFQ region.
Therefore an effective emittance growth due to the multi-charge beam
acceleration can be minimized.
