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 $Z_1^H(\omega )=-417.14i\mathrm{k}\mathrm{\Omega }/\mathrm{m}(\mathrm{horizontal})$ and $Z_1^V(\omega )=-530.19i\mathrm{k}\mathrm{\Omega }/\mathrm{m}(\mathrm{vertical})$, 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 $2\mu \mathrm{m}$-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 $Z_1^H(\omega )=-291.69i\mathrm{k}\mathrm{\Omega }/\mathrm{m}$ and $Z_1^V(\omega )=-352.37i\mathrm{k}\mathrm{\Omega }/\mathrm{m}$ to $Z_1^H(\omega )=-46.16i\mathrm{k}\mathrm{\Omega }/\mathrm{m}$ and $Z_1^V(\omega )=-64.56i\mathrm{k}\mathrm{\Omega }/\mathrm{m}$. Furthermore, in this case the transverse broadband impedance model of BRing is reduced by more than 50% to $Z_1^H(\omega )=-171.61i\mathrm{k}\mathrm{\Omega }/\mathrm{m}$ and $Z_1^V(\omega )=-242.38i\mathrm{k}\mathrm{\Omega }/\mathrm{m}$.