Background Circular electron positron collider(CEPC)is a 100-km electron positron collider proposed by IHEP.The longitudinal coupled-bunch instability(LCBI)of CEPC main ring operating to study the Z particle(Z machine...Background Circular electron positron collider(CEPC)is a 100-km electron positron collider proposed by IHEP.The longitudinal coupled-bunch instability(LCBI)of CEPC main ring operating to study the Z particle(Z machine)may be a limiting factor of CEPC and needs to be considered seriously.Purpose The purposes of this paper are to calculate the LCBI caused by the fundamental mode of superconducting RF cavities in CEPC main ring,which is the most critical impedance,and to complete the design of the RF feedback systems suitable for CEPC,whose specifications can suppress the LCBI to a manageable level.Methods The LCBI growth rate in the CEPC main ring is calculated in the frequency domain.Two kinds of RF feedback,i.e.,direct feedback and one-turn delay feedback,are simulated with the program to suppress the LCBI.And according to the suppression effect of LCBI growth rate after adding RF feedback,the required design parameters are given.Results Two operation conditions of Z machine have severe LCBI without suppression,and dozens of longitudinal modes are unstable.Only the direct RF feedback is needed to suppress LCBI in the case of Z-30 MW,while both the direct RF feedback with maximum gain and one-turn feedback are needed in the case of Z-50 MW.The LCBI growth rates can be reduced to the order of half frequency of the synchronous oscillation.Conclusion The LCBI of CEPC Z machine has been studied.Selecting appropriate feedback RF feedback can reduce the LCBI to an acceptable value that bunch by bunch feedback can suppress.展开更多
Introduction The circular electron-positron collider(CEPC)will use a 650-MHz RF system with 240 two-cell cavities for the collider.The collider is a double ring with shared cavities for Higgs operation and separate ca...Introduction The circular electron-positron collider(CEPC)will use a 650-MHz RF system with 240 two-cell cavities for the collider.The collider is a double ring with shared cavities for Higgs operation and separate cavities for W and Z operations.The higher-order modes(HOM)excited by the intense beam bunches must be damped to avoid additional cryogenic loss and multi-bunch instabilities.Materials and methods To get the real damping results,two prototypes of HOM coupler have been fabricated and installed on the 650-MHz two-cell cavity.The HOMs have been verified by bead pulling method.A test bench with two 2-cell cavities is used to measure the real damping results and study HOM propagating properties for a cavity string.Conclusion In this paper,the impedance budget,HOM damping and HOM power requirements for the CEPC collider ring are given.The damping results measured for the fundamental mode and HOMs seem good compared with the simulated results.The absorbing efficiency of the absorber and the extraction power efficiency of HOM couplers were also achieved.展开更多
The utility of a passive fourth-harmonic cavity plays a key role in suppressing longitudinal beam insta- bilities in the electron storage ring and lengthens the bunch by a factor of 2.6 for the phase I[ project of the...The utility of a passive fourth-harmonic cavity plays a key role in suppressing longitudinal beam insta- bilities in the electron storage ring and lengthens the bunch by a factor of 2.6 for the phase I[ project of the Hefei Light Source （HLS II ）. Meanwhile, instabilities driven by higher-order modes （HOM） may limit the performance of the higher-harmonic cavity. In this paper, the parasitic coupled-bunch instability, which is driven by narrow band parasitic modes, and the microwave instability, which is driven by broadband HOM, are both modeled analytically. The analytic modeling results are in good agreement with those of our previous simulation study and indicate that the passive fourth-harmonic cavity suppresses parasitic coupled-bunch instabilities and microwave instability. The modeling suggests that a fourth-harmonic cavity may be successfully used at the HLS II.展开更多
文摘Background Circular electron positron collider(CEPC)is a 100-km electron positron collider proposed by IHEP.The longitudinal coupled-bunch instability(LCBI)of CEPC main ring operating to study the Z particle(Z machine)may be a limiting factor of CEPC and needs to be considered seriously.Purpose The purposes of this paper are to calculate the LCBI caused by the fundamental mode of superconducting RF cavities in CEPC main ring,which is the most critical impedance,and to complete the design of the RF feedback systems suitable for CEPC,whose specifications can suppress the LCBI to a manageable level.Methods The LCBI growth rate in the CEPC main ring is calculated in the frequency domain.Two kinds of RF feedback,i.e.,direct feedback and one-turn delay feedback,are simulated with the program to suppress the LCBI.And according to the suppression effect of LCBI growth rate after adding RF feedback,the required design parameters are given.Results Two operation conditions of Z machine have severe LCBI without suppression,and dozens of longitudinal modes are unstable.Only the direct RF feedback is needed to suppress LCBI in the case of Z-30 MW,while both the direct RF feedback with maximum gain and one-turn feedback are needed in the case of Z-50 MW.The LCBI growth rates can be reduced to the order of half frequency of the synchronous oscillation.Conclusion The LCBI of CEPC Z machine has been studied.Selecting appropriate feedback RF feedback can reduce the LCBI to an acceptable value that bunch by bunch feedback can suppress.
基金supported by National Key Programme for S&T Research and Development(Grant No.:2016YFA0400400)National Natural Science Foundation of China(No.:11905232)Xie Jialin Funding from IHEP
文摘Introduction The circular electron-positron collider(CEPC)will use a 650-MHz RF system with 240 two-cell cavities for the collider.The collider is a double ring with shared cavities for Higgs operation and separate cavities for W and Z operations.The higher-order modes(HOM)excited by the intense beam bunches must be damped to avoid additional cryogenic loss and multi-bunch instabilities.Materials and methods To get the real damping results,two prototypes of HOM coupler have been fabricated and installed on the 650-MHz two-cell cavity.The HOMs have been verified by bead pulling method.A test bench with two 2-cell cavities is used to measure the real damping results and study HOM propagating properties for a cavity string.Conclusion In this paper,the impedance budget,HOM damping and HOM power requirements for the CEPC collider ring are given.The damping results measured for the fundamental mode and HOMs seem good compared with the simulated results.The absorbing efficiency of the absorber and the extraction power efficiency of HOM couplers were also achieved.
基金Supported by National Natural Science Foundation of China (10979045, 11175180, 11175182)
文摘The utility of a passive fourth-harmonic cavity plays a key role in suppressing longitudinal beam insta- bilities in the electron storage ring and lengthens the bunch by a factor of 2.6 for the phase I[ project of the Hefei Light Source （HLS II ）. Meanwhile, instabilities driven by higher-order modes （HOM） may limit the performance of the higher-harmonic cavity. In this paper, the parasitic coupled-bunch instability, which is driven by narrow band parasitic modes, and the microwave instability, which is driven by broadband HOM, are both modeled analytically. The analytic modeling results are in good agreement with those of our previous simulation study and indicate that the passive fourth-harmonic cavity suppresses parasitic coupled-bunch instabilities and microwave instability. The modeling suggests that a fourth-harmonic cavity may be successfully used at the HLS II.
