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Coupler Effects in High Energy Part of XFEL Linac

Coupler Effects in High Energy Part of XFEL Linac. Laboratory Report. V. Tsakanov CANDLE (Armenia). XFEL Beam Dynamics Group Meeting , 31 March 2008. Contents. Coupler RF and Wake field Effects Injector and Linac 1 Low energy Linac -0.5-2 GeV High Energy Linac – 2-20 GeV Summary.

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Coupler Effects in High Energy Part of XFEL Linac

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  1. Coupler Effects in High Energy Part of XFEL Linac Laboratory Report V. Tsakanov CANDLE (Armenia) XFEL Beam Dynamics Group Meeting , 31 March 2008

  2. Contents • Coupler RF and Wake field Effects • Injector and Linac 1 • Low energy Linac -0.5-2 GeV • High Energy Linac – 2-20 GeV • Summary

  3. Introduction Couplers : Wake Field , RF Distortion -Dipole term - Monopole term • Beam coherent oscillations • Head-Tail Relative kick • Wakefield Emittance dilution (Cavity wake) • Chromatic Emittance dilution ( Energy spread)

  4. Model for Transverse Potential The field potential - linear variation within the bunch W(s) S=0 • Coupler RF kick – • Scaling with accel grad and bunch length Krf ~ Vcav*σz Monopole term Dipole term

  5. E/E Beam Model for Particle Tracking  (s, E/E,x,x’,y,y’) x’ (y’) moments xx, x’x’,xx’ x (y) yy, y’y’,yy’ (s) Uncorrelated q(E/E) sk slices subslices q(sk),E(sk)

  6. 5MeV - 500MeV 0.5GeV - 2GeV 2GeV - 20GeV BC1 BC2 Monopole Dipole I.Zagorodnov, M. Dohlus Main Parameters Wake kick Wake kick RF kick Wake kick Cavity kick Cavity kick Monopole Dipole For cavity For beam offset < 1mm monopole term k0 dominates

  7. 5 MeV ACCEL1 ~100 MeV 8 cavities 12 MV/m LINAC1 ~100 MeV ~500 MeV 4 TESLA Modules ~ 12MV/m Injector Part Bunch Charge – 1nC Bunch rms length – 2mm Normalized emittance – 1mm*mrad

  8. Optics ( W. Decking)

  9. 5 MeV ACCEL1 ~100 MeV 8 cavities 12 MV/m ACCEL 1 Coupler RF Field & Wake Trajectory Emittance dilution Dominate by RF Head –tail kick by monopole term Cavity wake effect - < 0.1%

  10. 14% 7% 3.5% Other Options (??) β0=2.4 V1:α0=-4.2 V2: α0 =-3.0 V3: α0=-2.3 V1- Injector Design

  11. LINAC1 ~100 MeV ~500 MeV 4 TESLA Modules ~ 12MV/m LINAC1 Coupler RF Coupler Wake 0.25% ~5%

  12. Summary for Injector • Coupler RF Field effects • ACCEL1 – 5-100 MeV • Emittance growth ~14 % • Linac 1 – 100-500 MeV • Emittance growth ~5% • Other effects • RF Wake • Injection Jitter – 1 sigma offset • Cavity&Modules misal.-0.5mm • Cavity tilts – 0.5 mrad <1%

  13. Booster+Main Linac Summary of Emittance Dilution Booster Linac • Coherent oscillations uncorrelated6·10-62·10-4 correlated 2·10-31.2·10-3 • Cavity Misalignments 5·10-63·10-7 • Modules Misalignments 4·10-5 2.5·10-6 • Correlated Misal. (130o) - 7·10-6 • Cavity tilts uncorrelated5.8·10-50.6% correlated0.6%1.9% • One-to-One correction uncorrelated6.3·10-5 0.4% correlated 1.7% 2% Total Emittance dilution <5% with 2 Modules/Cell

  14. Wake RF kick Booster Linac 6 FODO cells • Dominate by RF Head –tail kick - monopole term • Natural global compensation

  15. Main Linac- Coupler Wake 52 FODO Cells – Betatron oscillations ~9 Accum. Emittance Dilution Correlated, Chromatic Monopole term - Offset independent wake

  16. D F Correlated Cavity tilts σtilt=0.5mrad Uncorrelated

  17. Summary • Coupler RF Field effects ACCEL1 – 5-100 MeV Emittance dilution - 14 % (Head Tail kick) Linac 1 – 100-500 MeV Emittance dilution – 5% (Head tail Kick) • Coupler Wake Effects Booster - 0.5-2 GeV Emittance dilution – 0.02% ( Head tail kick) Main Linac – 2-20 GeV Emittance dilution – 0.025% ( Chromatic)

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