Calculations for RF Cavities with Dissipative Material

For the design of RF devices like accelerating cavities, feeding and/or extracting RF energy requires antenna/waveguide ports, which present a perturbation to the otherwise closed system. Calculating Eigenmodes requires a numerical solver. The accurate numerical assessment and optimization of the external Q factors at such ports for a specifically excited RF mode or a mode ensemble can be crucial for proper operation of the device. Here a 3D Eigenmode solver technique is presented for the determination of the external Q, which makes use of dissipative material at external ports rather than the more traditional method of resembling matched conditions at external ports via the calculation of waveguide modes. This has advantages since both the external Q factor and the loaded frequency are calculated as part of the Eigenmode solver run (complex solution), while allowing for travelling mode conditions instead of standing waves. The technique does not require the external Q to be evaluated from subsequent runs with magnetically and electrically (closed) boundaries.