Transverse broadband impedance reduction techniques in a heavy ion accelerator

Abstract

The transverse broadband impedances of major components in the BRing (booster ring) of HIAF (High Intensity Heavy-ion Accelerator Facility) are estimated using the analytical formulas or the wakefield solver in the CST Studio Suite. At low frequency, the transverse broadband impedance model of BRing is ${Z}_{1}^{H}(\ensuremath{\omega})=\ensuremath{-}417.14i\text{ }\text{ }\mathrm{k}\mathrm{\ensuremath{\Omega}}/\mathrm{m}(\mathrm{horizontal})$ and ${Z}_{1}^{V}(\ensuremath{\omega})=\ensuremath{-}530.19i\text{ }\mathrm{k}\mathrm{\ensuremath{\Omega}}/\mathrm{m}(\mathrm{vertical})$, which are larger than the threshold impedance for the transverse mode-coupling instability. The ceramic rings in the vacuum chamber are the primary source of impedance. With a goal of mitigating the instability by reducing the impedance of ceramic rings, a high conductivity coating is discussed in detail. In addition, a prototype of ceramic rings-loaded thin-wall vacuum chamber is manufactured and the impedance measurements are performed. When ceramic rings are coated by $2\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$-copper, the CST simulation and experiment results show that the transverse broadband impedance of ceramic rings-loaded thin-wall vacuum chamber can be reduced from ${Z}_{1}^{H}(\ensuremath{\omega})=\ensuremath{-}291.69i\text{ }\mathrm{k}\mathrm{\ensuremath{\Omega}}/\mathrm{m}$ and ${Z}_{1}^{V}(\ensuremath{\omega})=\ensuremath{-}352.37i\text{ }\mathrm{k}\mathrm{\ensuremath{\Omega}}/\mathrm{m}$ to ${Z}_{1}^{H}(\ensuremath{\omega})=\ensuremath{-}46.16i\text{ }\mathrm{k}\mathrm{\ensuremath{\Omega}}/\mathrm{m}$ and ${Z}_{1}^{V}(\ensuremath{\omega})=\ensuremath{-}64.56i\text{ }\text{ }\mathrm{k}\mathrm{\ensuremath{\Omega}}/\mathrm{m}$. Furthermore, in this case the transverse broadband impedance model of BRing is reduced by more than 50% to ${Z}_{1}^{H}(\ensuremath{\omega})=\ensuremath{-}171.61i\text{ }\text{ }\mathrm{k}\mathrm{\ensuremath{\Omega}}/\mathrm{m}$ and ${Z}_{1}^{V}(\ensuremath{\omega})=\ensuremath{-}242.38i\text{ }\text{ }\mathrm{k}\mathrm{\ensuremath{\Omega}}/\mathrm{m}$.