Beam Coupling Impedance Analyze Using Bunch-by-Bunch Measurement
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X.Y. Xu
University of Chinese Academy of Sciences, Beijing, People’s Republic of China
Y.B. Leng, X.Y. Xu
SSRF, Shanghai, People’s Republic of China
X.Y. Xu
SINAP, Shanghai, People’s Republic of China
Beam coupling impedance is very important parameters for advanced synchrotron radiation facilities. Till now there is no online method to measure beam impedance directly. But some beam parameters such as betatron tune amplitude and frequency, synchrotron phase, bunch lifetime and so on, can be modulated by beam impedance effects. So wake field and beam impedance information could be retrieved by measuring bunch-by-bunch beam 3D positions and analyzing bunch index dependency of above beam parameters. A bunch-by-bunch 3D positions and charge measurement system had been built at SSRF for this purpose and the performance is not good enough for beam impedance analyze due to cross talk between bunches. We upgraded the measurement system to minimize cross talk and improve resolution this year. New beam experiment results and corresponding analyze will be introduced in this paper.
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J. Chen, S.S. Cao, F.Z. Chen, B. Gao, L.W. Lai, Y.B. Leng, T. Wu, X.Y. Xu, R.X. Yuan, Y.M. Zhou
SSRF, Shanghai, People’s Republic of China
Precise bunch charge measurement is the fundamental of charge feedback, beam lifetime measurement, beam loss monitor, as well as the basis of the related interlocking work. Beam position monitor (BPM) is often used for high-precision bunch charge measurement due to its superior performance. In this paper, the pros and cons of different types of BPM for measurement of bunch charge in storage ring and free electron laser (FEL) will be discussed. The related simulations, beam experiment and signal processing methods are also mentioned. The beam experiments results show that the relative bunch charge resolution of the Button BPM can reach 0.02％ in SSRF, 0.073％ and 0.021％ of the SBPM and CBPM in SXFEL, respectively. Besides, based on the method of beam experiments, we systematically studied the position dependence of BPM pickup and related compensation algorithms for high-precision bunch charge measurement.
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