High order mode power loss evaluation in future circular electron-positron collider cavities

Abstract

The high order mode (HOM) power losses induced by a particle beam in accelerator components should be taken into account during their design and the choice of HOM couplers. In this work the power losses due to HOMs in the proposed 400.79 MHz radio frequency (rf) cavity designs were evaluated for various energy options (Z, W, H, and $\mathrm{t}\overline{\mathrm{t}}$) of the future circular electron-positron collider (FCC-ee). The constraints for the rf cavity design are dictated by the Z machine with the lowest beam energy, but the highest beam current. Still certain beam filling patterns (bunch and train spacings) are not feasible and should be avoided in beam operation. For other energy options the power loss are sufficiently low and can be extracted by conventional HOM couplers.