Superconducting cavities for the reduced-beta section of a proton linac

A proton linear accelerator with energies beyond 1.0 GeV has been proposed where the LEP2 superconducting cavities are to be used after decommissioning of LEP, in the high energy part of the linac. Energies ranging from 100 MeV to 1.0 GeV will be covered by superconducting cavities designed to accelerate protons with reduced value of beta. The basic idea is to keep the shape of the spherical LEP cavities for β=1.0 and to adjust their length, for β<1.0 in order to get an optimal acceleration for low energy protons. Three different values of β allow to cover the required range with a reasonable acceleration efficiency. The design of superconducting cavities for β=0.50, 0.625 and 0.80 is presented. In particular the choice of an elliptic iris profile is discussed