MOP2WA —  WG-A   (18-Jun-18   16:00—18:00)
Chair: Y.H. Chin, KEK, Ibaraki, Japan
Paper Title Page
MOP2WA01 Beam Physics Limitations for Damping of Instabilities in Circular Accelerators -1
  • V.A. Lebedev
    Fermilab, Batavia, Illinois, USA
  Funding: Work supported by D.O.E. Contract No. DE-AC02-07CH11359
The paper considers a beam interaction with a feedback system and major limitations on the beam damping rate. In particular, it discusses: limitations on the system gain and damping rate, feedback system noise and its effect on the beam emittance growth, x-y coupling effect on damping, suppression of high order modes and damping of slip-stacked beams.
slides icon Slides MOP2WA01 [0.408 MB]  
Chromaticity Effects on Head-Tail Instabilities for Broadband Impedance Using Two Particle Models, Vlasov Analysis, and Simulations  
  • Y.H. Chin
    KEK, Ibaraki, Japan
  This talk is about Chromaticity effects on head-tail instabilities for broadband impedance using two particle models, Vlasov analysis, and simulations.  
slides icon Slides MOP2WA02 [3.909 MB]  
MOP2WA03 Experiments and Theory on Beam Stabilization with Second-Order Chromaticity -1
  • M. Schenk, X. Buffat, L.R. Carver, K.S.B. Li, E. Métral
    CERN, Geneva, Switzerland
  • A. Maillard
    ENS, Paris, France
  This study reports on an alternative method to generate transverse Landau damping to suppress coherent instabilities in circular accelerators. The incoherent betatron tune spread can be produced through detuning with longitudinal rather than transverse action. This approach is motivated by the high-brightness, low transverse emittance beams in future colliders where detuning with transverse amplitude will be less effective. Detuning with longitudinal action can be introduced with a radio frequency (rf) quadrupole, or similarly, using second-order chromaticity. The latter was enhanced in the Large Hadron Collider (LHC) at CERN and experimental results on single-bunch stabilization are briefly recapped. The observations are interpreted analytically by extending the Vlasov formalism to include nonlinear chromaticity. Finally, the newly developed theory is benchmarked against circulant matrix and particle tracking models.  
slides icon Slides MOP2WA03 [3.374 MB]  
MOP2WA04 Recent Results from the Wideband Feedback System Tests at the SPS and Future Plans -1
  • K.S.B. Li, H. Bartosik, M.S. Beck, E.R. Bjørsvik, W. Höfle, G. Kotzian, T.E. Levens, M. Schenk
    CERN, Geneva, Switzerland
  • J.E. Dusatko, J.D. Fox, C.H. Rivetta
    SLAC, Menlo Park, California, USA
  • M. Schenk
    EPFL, Lausanne, Switzerland
  • O. Turgut
    Stanford University, Stanford, California, USA
  A high bandwidth transverse feedback demonstrator system has been devised within the LARP framework in collaboration with SLAC for the LHC Injectors Upgrade (LIU) Project. The initial system targeted the Super Proton Synchrotron (SPS) at CERN to combat TMCI and electron cloud instabilities induced for bunches with bunch lengths at the 100 MHz scale. It features a very fast digital signal processing system running at up to 4~GS/s and high bandwidth kickers with a frequency reach of ultimately beyond 1~GHz. In recent years, the system has gradually been extended and now includes two stripline kickers for a total power of 1~kW delivering correction signals at frequencies of currently more than 700~MHz. This talk will cover recent studies using this demonstrator system to overcome TMCI limitations in the SPS. We will conclude with future plans and also briefly mention potential applications and requirements for larger machines such as the LHC or the HL-LHC.  
slides icon Slides MOP2WA04 [19.091 MB]  
MOP2WA05 Simulation and Measurement of the TMCI Threshold in the LHC -1
  • D. Amorim, S. A. Antipov, N. Biancacci, X. Buffat, L.R. Carver, E. Métral
    CERN, Geneva, Switzerland
  The transverse mode coupling instability occurs in individual bunches when two transverse oscillation modes couple at high intensity. Simulations predict an instability threshold in the LHC at a single bunch intensity of 3*1011 protons. The TMCI threshold can be inferred by measuring the tune shift as a function of intensity. This measurement was performed in the LHC for different machine impedances and bunch intensities. The impedance was changed by varying the primary and secondary collimators gaps to increase their contribution to the resistive wall impedance. The experiment also allowed to assess the validity of the LHC impedance model in the single bunch case.  
slides icon Slides MOP2WA05 [4.729 MB]