CHALLENGES AND THE FUTURE OF REDUCED-BETA SRF CAVITY DESIGN*

Superconducting radio frequency (SRF) linacs have been one of the structures of choice in the intense proton accelerator and the heavy ion accelerator for intense neutron sources, nuclear transmutation, energy amplifiers, rare isotopes accelerator, etc. For these applications, there are strong demands of reduced-beta (β<1) SRF cavity. In this paper two types of cavities are considered. One is the well-known multi-cell elliptical cavity adapted from electron accelerator. It has been shown that the multi-cell elliptical cavity is a very suitable structure for betas above 0.5. Below this value, the operation would be difficult due to its weak mechanical characteristics. The other is the spoke cavity that is considered as a promising SRF cavity structure that could cover beta ranges from 0.1 to 0.5. General considerations and the related optimizations in the design and the corresponding analysis are studied by exploring physical parameter spaces of each cavity type, on the basis of design criteria