Simulation and experiments for the Q_ext of a cavity beam position monitor

Abstract: 

The external Q (Q_ext) of the dipole mode is a key parameter of the Cavity Beam Position Monitor (CBPM). It determines the amplitude and length of the dipole mode signal. In this paper, Q_ext of a CBPM whose waveguides were open to the air was simulated and measured, and the results agreed with each other. Then four waveguide-to-coaxial cable adpaters were adjusted and assembled to the CBPM, and Q_ext remained unchanged. This progress provides a reliable method to evaluate Q_ext in the physics design without simulating the structurally complex adapters.