External Fast Electrically-Controlled Ferroelectric Tuners for SRF Cavities

Microphonics in SRF cavities refers to the cavity frequency detune driven by external vibration sources. As the cavities detune, additional RF power is required to maintain the accelerating gradient which significantly increases both the acquisition cost and the operational cost of the machine. Currently the methods to compensate microphonics have less effectiveness or reliable for the SRF cavities being installed in a cryomodule. This issue is particularly critical in energy recovery linear accelerators (ERLs) and heavy ion accelerators. The principal objective of our proposal is to apply Euclid’s fast ferroelectric tuning technology for microphonics compensation on SRF cavities in RF power configurations that combine the RF power source (klystron) and the fast active tuner at the same cavity port. This new technology will be applied to one of CEBAF’s C100 cryomodules. In principle it can save more than 20% of RF power in CEBAF, thus significant improve the facility efficiency and reduce the operation cost. For Phase I, in order to evaluate the advantages of this technique, we will carry out a feasibility study on the use of the ferroelectric technology in a magic-T configuration that will allow its use with a single RF port connected to the cavity. We will modify the low-level RF (LLRF) electronics of the C100 tuner and optimize it. We will also design a fast ferroelectric tuner that is optimized for the higher power levels set by the C100 cryomodule’s requirements, and fabricate and test the ferroelectric tuning elements. A conceptual design of a fast ferroelectric tuner for the elliptical SRF cavities of the FRIB energy upgrade will be developed. In a world’s first, CERN recently tested Euclid’s prototype ferroelectric tuner with a superconducting cavity, and successfully demonstrated frequency tuning. This is a significant step forward in the development of an entirely new class of tuners that will allow electronic control of cavity frequencies by a device operating at room temperature and at timescales that will allow active compensation of microphonics. For many applications, this could eliminate the need for additional RF power to mitigate the microphonics, thus significantly reducing the required RF amplifier power.