Keyword: impedance
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TUT3AH1 Collective Effects Issues for FCC-ee ion, wakefield, radiation, synchrotron 100
 
  • M. Migliorati
    University of Rome La Sapienza, Rome, Italy
  • E. Belli
    CERN, Geneva, Switzerland
  • G. Castorina, B. Spataro, M. Zobov
    INFN/LNF, Frascati (Roma), Italy
  • S. Persichelli
    LBNL, Berkeley, California, USA
  
  The Future Circular Collider study, hosted by CERN to design post-LHC particle accelerator options in a worldwide context, represents a great challenge under several aspects, which require R&D on beam dynamics and new technologies. One very critical point is represented by collective effects, generated by the interaction of the beam with self-induced electromagnetic fields, called wake fields, which could produce beam instabilities, thus reducing the machines performance and limiting the maximum stored current. It is therefore very important to be able to predict these effects and to study in detail potential solutions to counteract them. In this paper the resistive wall and some other important geometrical sources of impedance for the FCC electron-positron accelerator are identified and evaluated, and their impact on the beam dynamics, which could lead to unwanted instabilities, is discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2016-TUT3AH1  
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TUT3AH2 Instability Issues in CEPC ion, cavity, damping, coupling 108
 
  • N. Wang, W. Chou, J. Gao, D.J. Gong, J. He, Q. Qin, Y.S. Sun, D. Wang, Y. Wang, G. Xu, Y. Zhang, H.J. Zheng
    IHEP, Beijing, People's Republic of China
  • K. Ohmi, D. Zhou
    KEK, Ibaraki, Japan
  
  The CEPC is a high energy circular electron-positron collider under design. Large bunch population is required to achieve the design luminosity. Instabilities driven by the coupling impedance are possible limitations for reaching high machine performance. An updated impedance model, including the resistive wall and the main vacuum components, has been obtained for the main ring. Based on the impedance model, the collective instability issues of the beam with the partial-double ring design are discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2016-TUT3AH2  
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TUT3AH3 Beam-based Impedance Measurement Techniques ion, vacuum, simulation, damping 112
 
  • V.V. Smaluk
    BNL, Upton, Long Island, New York, USA
  
  Funding: Work supported by DOE under contract No.DE-AC02- 98CH10886
Characterization of a vacuum chamber impedance is necessary to estimate stability conditions of a particle beam motion, to find a limit of the beam intensity and characteristic times of single-bunch and multi-bunch instabilities. For new accelerator projects, minimization of the vacuum chamber impedance is now the mandatory requirement. For an accelerator in operation, the impedance can be measured experimentally using various beam-based techniques. The beam-impedance interaction manifests itself in measurable beam parameters, such as betatron tunes, closed orbit, growth rates of instabilities, bunch length and synchronous phase. The beam-based techniques developed for measurement of the longitudinal and transverse impedance are discussed, including theoretical basics and experimental results. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2016-TUT3AH3  
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TUT3AH7 Electron Cloud and Collective Effects in the Interaction Region of FCC-ee ion, electron, simulation, quadrupole 130
 
  • E. Belli, G. Rumolo
    CERN, Geneva, Switzerland
  • E. Belli
    University of Rome "La Sapienza", Rome, Italy
  • E. Belli
    INFN-Roma, Roma, Italy
  • M. Migliorati
    University of Rome La Sapienza, Rome, Italy
  • M. Migliorati
    INFN-Roma1, Rome, Italy
  
  The FCC-ee is an e+e− circular collider designed to accommodate four different experiments in a beam energy range from 91 to 350 GeV and is a part of the Future Circular Collider (FCC) project at CERN. One of the most critical aspects of this new very challenging machine regards the collective effects which can produce instabilities, thus limiting the accelerator operation and reducing its performance. The following studies are focused on the Interaction Region of the machine. This talk will present preliminary simulation results of the power loss due to the wake fields generated by the electromagnetic interaction of the beam with the vacuum chamber. A preliminary estimation of the electron cloud build-up is also reported, whose effects have been recognized as one of the main limitations for the Large Hadron Collider at CERN.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2016-TUT3AH7  
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THS2H1 Summary of Impedance Issues and Beam Instabilities ion, electron, feedback, wakefield 210
 
  • F. Zimmermann
    CERN, Geneva, Switzerland
  
  Funding: This work was supported in part by the European Commission under the FP7 Capacities project EuCARD-2, grant agreement 312453.
This paper summarizes the session on impedance issues and beam instabilities at the ICFA workshop on future circular electron-positron factories "eeFACT2016" held at the Cockcroft Institute, Daresbury, from 24 to 27 October 2016. This session also covered active beam stabilization by feedback systems. Beam-beam effects and coherent beam-beam instabilities were addressed separately and, therefore, are not included here. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2016-THS2H1  
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