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}(ω)=-417.14i kΩ/m(horizontal) and Z_{1}^{V}(ω)=-530.19i kΩ/m(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 μm-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}(ω)=-291.69i kΩ/m and Z_{1}^{V}(ω)=-352.37i kΩ/m to Z_{1}^{H}(ω)=-46.16i kΩ/m and Z_{1}^{V}(ω)=-64.56i kΩ/m. Furthermore, in this case the transverse broadband impedance model of BRing is reduced by more than 50% to Z_{1}^{H}(ω)=-171.61i kΩ/m and Z_{1}^{V}(ω)=-242.38i kΩ/m.