Optimization of a 1.5-GHz Two-Cell SRF Cavity

A two-cell niobium cavity with the π-mode resonance frequency of 1.5 GHz was designed and optimized with multiphysics finite element simulations in this study. Its geometry was scaled from the 500-MHz KEKB-type single-cell SRF cavity but with straight sections at both the equators and the connection between both cavity cells. The lengths of these two straight sections have significant effects on the RF resonance frequency and accelerating performance. Numerical models were established to find optimized combination of these two lengths by taking both the cooling down to 4.2 K and the external pressure of 101.3 kPa into consideration. Considerations and processes on the optimization are presented. After optimization, the π-mode frequency is 1.499516 GHz at an R/Q of 96.86 Ω, all meeting operational requirements.