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Optimizing 800 MHz Cavity Design: Beam Impedance Considerations at CERN

This meeting on beam impedance calculations for HiLumi LHC at CERN discusses preliminary considerations for an 800 MHz cavity HOM-free design. Emphasizing the need for a small beam coupling impedance and low R/Q for beam transients, the focus is on a single-cell design with specific parameters and geometry optimization. The session also explores multipacting simulations, HOM suppression techniques, and different designs for effective performance. More precise requirements from beam dynamics and mechanical constraints are essential for advancing the cavity design process.

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Optimizing 800 MHz Cavity Design: Beam Impedance Considerations at CERN

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  1. Meeting on Beam Impedance Calculations for HiLumi LHC, CERN, 29 October 2013 Preliminary Considerations on 800 MHz Cavity HOM-Free Design M. Zobov, A. Gallo LNF INF, Frascati, Italy R. Bolgov, M. Gusarova, Ya. Shashkov, N. Sobenin MEPHI, Moscow, Russia

  2. We do not know yet exact requirements coming from: • Beam dynamics • Geometrical constraints Why “Preliminary”? • Beam coupling impedance should be as small as possible • Not very high R/Q because of beam transients • Required volatge of 8 MV • Single cell design preferable What we know

  3. Working point chosen r1 r2 rC rB lCELL/2 L.Ficcadenti et al., CERN

  4. 800 MHz Cavity Modes (Baseline design) R/Q of Cavity Modes

  5. Cavity with damping couplers L.Ficcadenti et al., CERN

  6. Since high R/Q is not required it is worthwhile to exploit the “single mode” cavity design: • Relatively Simple • No HOMs From KEKB Design Report

  7. Geometry Optimization H111 (Electric Field) E110 (Electric Field) Drift Tube Radius: 85 mm Drift Tube Radius: 100 mm Drift Tube Radius: 85 mm

  8. Fundamental Mode f = 800 MHz, R/Q0 = 53.33, Q0 = 1.91x1010

  9. Cut-off E01 => 1.35 GHz

  10. Fast rise Cut-off H11 => 1.03 GHz Slower decay

  11. Multipacting simulations for the SC cavities – MultP-M code Possible multipacting for Ez in the range from 1.7-7 MV/m No stable trajectories are found

  12. TE111 at 1068 MHz IElectric FieldI

  13. Main coupler

  14. sz = 7.5 cm

  15. 4 Cavities?

  16. Cavity with highly resistive insertion and notch filter Notch filter Insertion MEPHI + LNF INFN

  17. HOM Suppression with Resistive Damping Rings w pos H111 Q0 = 1.57x1010 (w = 0 mm) E010  Q0 = 1.91x1010 (w = 0 mm) E011  Q0 = 1.57x1010 (w = 0 mm)

  18. Accepted for publication in NIM

  19. Considered Different Designs with Radial Lines Can be effective for HOM suppression! MEPHI + LNF INFN

  20. To conclude: In order to proceed with the cavity design we need more precise indications on requirements imposed by both beam dynamics and by mechanical constraints (allowable space, beam pipe radius, required power, cryostat etc.)

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