Coupling impedances of a gap in vacuum chamber

真空チェンバーのギャップのインピーダンス

菖蒲田 義博   ; Chin, Y. H.*; 高田 耕治*

Shobuda, Yoshihiro; Chin, Y. H.*; Takata, Koji*

We will present the formulae for the longitudinal and transverse impedances due to a gap in the beam chamber. In this process, we will derive the complete solutions of electro-magnetic fields effective in the entire region, including the inside and outside of the chamber, in the form that they can be easily numerically evaluated. The numerical results of impedances are consistent with the ABCI results and their behavior in high frequency agrees well with the prediction of the diffraction theory. Our theory can also accurately reproduce the behavior of the impedance near and above the cut-off frequencies. In addition, our theory is applicable even to the impedances for non-relativistic beams. We found that the broadband impedance of the small cavity-like structure can be estimated from the gap size and the chamber radius only. We also found that the transverse impedance of a gap has a large resonance peak at the frequency where the wavelength is equal to the chamber circumference.