Optimization of Two-Cell Cavities for the W and H Working Points of the FCC-ee Considering Higher-Order Mode Effects

The lepton collider of the future circular collider (FCC-ee) aims at conducting precision measurements on the Z, W, and H bosons and the top quark. The present RF baseline considers single-cell cavities at 400 MHz for the high current Z-pole working point, four-cell 400 MHz cavities for the W and H working points, and a hybrid RF system composed of four-cell 400 MHz and five-cell 800 MHz cavities for the high energy tt working point. The W working point has shown limitations in the achievable HOM damping for beam stability requirements using four-cell cavities. A two-cell cavity is studied as an alternative scenario for the current W- and H-RF setups with a special focus on HOM damping during the optimization of the RF geometry.