Performance Enhancements Of Low-β Superconducting Cavity

Superconducting RF (SRF) cavities are probably the most expensivecomponents in an accelerator. Scientists have put a lot of efforts into itsperformance enhancement and cost reduction. Using the low-beta SRF cavitiesat Facility for Rare Isotope Beams (FRIB) as examples, we have carried outsystematic studies to find effective methods to improve their performance. Thissystematic research includes topics from cavity structural optimization toadvanced control techniques, and also effective physics models to predictmultipacting suppression. These methods and designs are or will be adopted inFRIB cavity development. Preliminary test results are presented in this thesis asvalidation of the models.Following a brief introduction on SRF cavity’s fundamentals, we generallydescribe FRIB project and its procured cavities that were installed atRe-accelerator3(ReA3) in Chapter1. Our research was motivated by thechallenging during the commissioning of those SRF cavities, which is mainlydiscussed in Chapter2-4.Chapter2introduces our progresses on the structural optimization, usingFRIB β=0.085QWR as a sample. The new design significantly enhances theaccelerating gradient by reducing magnetic field and increasing shuntimpedance. Chapter3compares two control algorithms in low level RF controland tuner control: conventional Proportional Integral (PI) algorithm and anadvanced algorithm--Active Disturbance Rejection Control (ADRC). Chapter4discusses our important work on the multipacting suppression. Two modelswere developed: one for coaxial structure that leads to a new optimizedcoupler to be installed on FRIB cavities; another for the cavity’s short plate toreduce the multipacting on it.In the summarized Chapter5, we compare the effectiveness of the threeoptimizations. In the future, we will continue working on optimizing thedesign of SRF cavity and improving its performance.