Canceling evanescent waves in high-energy superconducting rf linacs

Abstract

Many future projects plan using high-current, high-energy, multipass energy-recovery linacs that are based on superconducting rf (SRF) cavities. The necessity of ensuring the transverse stability of the beam in such accelerators imposes strict limits on the high order modes (HOMs) impedances, and demands effective HOM damping. The latter requirement often precludes achieving a high real-estate accelerating gradient in such structures. The modular structure of long SRF linacs also requires incorporating vacuum flanges; however, these flanges have surface contacts and cannot tolerate strong rf fields. Locating them in the low-field areas of the linac structure may involve considerably elongating the intermodular interfaces, a change that would reduce the linac’s real-estate accelerating gradient. In this paper, I propose a novel method to resolve this issue, using compact interconnects between the SRF cavities wherein to locate effective HOM dampers and vacuum flanges.