Cavities for JLab's 12 GeV upgrade

The future 12 GeV upgrade of CEBAF requires new cryomodules in both linacs to increase the energy gain per pass to 1090 MeV. Until recently, the design of new cryomodules, which should deliver on average operational voltage of 70 MV each, was based on 7-cell superconducting cavities that are an extended version of the 5-cell structures currently used in the machine. The 5-cell cavities were constructed 20 years ago at Cornell University (Original Cornell-shape) for the Cornell Electron Storage Ring (CESR). The geometry of these structures met specifications at the time CESR was constructed but is not optimized for the future operation of CEBAF. Two improved cavity shapes have been proposed. This contribution presents the RF features of both new shapes and discusses advantages for the machine operation resulting from the improvement. In addition, we comment on the measurements on copper models of both new cavities and present results of the multipacting calculations.