THP1WB —  WG-B   (08-Mar-18   14:00—15:30)
Chair: Q. Qin, IHEP, Beijing, People's Republic of China
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Survey of Collective Effects in Next-Generation Light Source Rings  
  • R. Nagaoka
    SOLEIL, Gif-sur-Yvette, France
  In this talk we shall attempt to make an overview the general trend in storage rings optimized for the next-generation light sources, in the context of having as a result an important impact on beam collective effects. Reduction of the beam chamber cross section to attain strong magnetic fields for the ultra-low emittance optics is particularly highlighted. A series of collective effects and beam instabilities that are likely to get enhanced shall be reviewed. Some of the recent related theoretical, numerical and experimental studies shall be introduced, along with methods that are considered to be effective in mitigating the former undesirable effects.  
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THP1WB02 Impedance Evaluation of PF In-Vacuum Undulator (IVU) with Theories and Simulations and Experimental Confirmation of them by the Tune Measurement 160
  • O. Tanaka, N. Nakamura, T. Obina, K. Tsuchiya
    KEK, Ibaraki, Japan
  Four In-Vacuum Undulators (IVU) were recently installed to Photon Factory (PF) at KEK. The estimate of their impedance and kick factors is a very important issue, because they could considerably increase the total impedance of PF. Moreover, the coupling impedance of the IVUs could lead to the beam energy loss, changes in the bunch shape, betatron tune shifts and, finally, to the various beam instabilities. Using the simulation tool (CST Particle Studio), longitudinal and transverse impedances of the IVUs were evaluated and compared to analytical formulas and measurement results. The study provides guidelines for mitigation of unwanted impedance, for an accurate estimate of its effects on the beam quality and beam instabilities and for the impedance budget of a newly designed next-generation machine which has many IVUs and small-aperture beam pipes.  
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Theory of Longitudinal Multibunch Instabilities Including a Higher-Harmonic (Bunch-Lengthening) Cavity  
  • R.R. Lindberg
    ANL, Argonne, Illinois, USA
  Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
The next generation of high-brightness storage rings typically require a higher-harmonic rf system to increase the bunch length and improve lifetime. The modified longitudinal dynamics has important implications for multi-bunch stability, since bunch lengthening also changes the synchrotron frequency both by lowering its mean (which reduces stability), and by increasing its variation with amplitude (which gives rise to Landau damping). To understand these competing effects, we present an analytic theory of longitudinal multi-bunch instabilities in the presence of a higher-harmonic cavity tuned to lengthen the bunch. The theory results in a relatively straightforward extension to the usual matrix-based multi-bunch analysis, and we show how the numerically determined growth rates can be used to understand the role of Landau damping. Finally, we compare predictions of the theoretical growth rates to those extracted from tracking simulations of the proposed APS Upgrade lattice.
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