700 MHZ low-loss electrically-controlled fast ferroelectric phase shifter for ERL applications

A fast, electrically-controlled phase shifter is described with parameters suitable for operation with the SC acceleration structure of the Energy Recovery Linac (ERL) for the electron cooling system of the Relativistic Heavy Ion Collider (RHIC) at BNL. The phase shifter is a key element of the external RF vector modulator that is capable of fast tuning of the cavities to compensate for microphonics, Lorentz force and beam instabilities in a way that can possibly lead to an order of magnitude reduction in the required RF power. The phase shifter is based on a shortened low-impedence coaxial line containing ferroelectric rings. The dielectric constant of the ferroelectric rings is altered by applying a 0 to 4.2 kV voltage that provides an RF phase shift from 0deg to 180deg.