Nuclear Science and Techniques

《核技术》(英文版) ISSN 1001-8042 CN 31-1559/TL     2019 Impact factor 1.556

Nuclear Science and Techniques ›› 2020, Vol. 31 ›› Issue (5): 45

• SYNCHROTRON RADIATION TECHNOLOGY AND APPLICATIONS •

Examining RF jitter and transverse mode-coupling instability in triple-frequency RF systems

Shi-Chang Jiang 1, 2,  Gang Xu1, 2

1. 1 Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
University of Chinese Academy of Sciences, Beijing 100049, China
• Received:2019-12-03 Revised:2020-03-07 Accepted:2020-03-11
• Contact: Shi-Chang Jiang E-mail:jiangsc@ihep.ac.cn
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Shi-Chang Jiang, Gang Xu. Examining RF jitter and transverse mode-coupling instability in triple-frequency RF systems.Nuclear Science and Techniques, 2020, 31(5): 45
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Abstract: A longitudinal accumulation scheme based on a triple-frequency RF system, in which the static radio frequency (RF) bucket is lengthened to be compatible with the realizable raise time of a fast pulse kicker, is proposed in this paper. With this technique, the bunch from a booster can be captured by the longitudinal acceptance without any disturbance to the stored bunch, which remains at the center. This composite RF system consists of three different frequencies, which can be regarded as the conventional bunch lengthening RF system (usually containing fundamental and third harmonic cavities) extended by an additional second harmonic RF cavity. In this paper, we discuss the RF jitter and the transverse mode-coupling instability (TMCI) when using this special RF system. Considering several different bunch profiles, we discuss the beam stability with regard to the RF jitter. However, for the TMCI we assume an ideal bunch profile, where the bunch is exactly lengthened to the maximum extent. While macro-particle simulation is the main method used to study the impact of the RF jitter, numerical analysis and simulations for the TMCI while using a triple-frequency RF system are also presented in this paper. An approximation formula, based on the existing model, is also derived to estimate the impact of the TMCI on the single bunch current threshold when using harmonic cavities.