Superconducting H-mode Structures for Medium-Energy Beams

Room temperature IH-type drift tube structures are used at different places now for the acceleration of ions with mass over charge ratios up to 65 and velocities between 0.016 c and 0.1 c. These structures have a high shunt impedance and allow the acceleration of very intense beams at high accelerating gradients. The overall power consumption of room temperature IH-mode structures is comparable with superconducting (sc) structures up to 2 MeV/u. With the KONUS [1] beam dynamics, the required transversal focusing elements, e.g. quadrupole triplets can be placed outside of multicell cavities, which is favourable for building sc H-mode cavities. The design principles and consequences to the geometry compared to room temperature (rt) cavities will be described. The results gained from numerical simulations show that a sc multi-gap H21(0)-mode cavity (CH-type) can be an alternative to the sc spoke-type or reentrant cavity structures up to beam energies around 150 MeV/u. The main cavity parameters and possible fabrication options will be discussed. [1] U. Ratzinger, Nucl. Intr. Meth., A 415 (1998) 229.