Third Harmonic Cavity Modal Analysis

TL;DR

This paper analyzes the electromagnetic modes of third harmonic cavities used in particle accelerators, employing circuit models and mode matching techniques to assess their performance and sensitivity to fabrication errors.

Contribution

It introduces an enhanced circuit model including successive cell coupling and a mode matching code for rapid simulation of cavity modes with fabrication errors.

Findings

Enhanced circuit model accurately predicts monopole band behavior.

Mode matching code enables quick analysis of fabrication errors.

Sensitivity analysis informs cavity design improvements.

Abstract

Third harmonic cavities have been designed and fabricated by FNAL to be used at the FLASH/XFEL facility at DESY to minimise the energy spread along the bunches. Modes in these cavities are analysed and the sensitivity to frequency errors are assessed. A circuit model is employed to model the monopole bands. The monopole circuit model is enhanced to include successive cell coupling, in addition to the usual nearest neighbour coupling. A mode matching code is used to facilitate rapid simulations, incorporating fabrication errors. Curves surfaces are approximated by a series of abrupt transitions and the validity of this approach is examined