Beam-beam simulations of hadron colliders

1. Beam-beam simulations of hadron colliders Tanaji Sen FNAL

2. Why simulate • Design a future collider • Understand observations in an existing collider • Improve the performance of an existing collider Beam-beam Simulations - T. Sen

3. Hadron Colliders • Tevatron • Classical “weak-strong” regime • Impact of long-range interactions • Impact of head-on collisions • RHIC • Coherent modes • LHC • Several long-range interactions • “Strong-strong” regime Beam-beam Simulations - T. Sen

4. Simulation Codes Beam-beam Simulations - T. Sen

5. Dynamic Aperture at 150 GeV Measured Simulation Beam-beam Simulations - T. Sen

6. Lifetime vs. Chromaticity – 150 GeV Diffusion coefficients - BBSIM Pbar lifetimes ~ 1hr when chromaticities = 8 units Pbar lifetimes > 5 hrs when chromaticities ~ (4,2) units with transverse dampers A. Kabel - PlibB Beam-beam Simulations - T. Sen

7. Pbar loss during squeeze Old helix New helix Pbar intensity No loss @ min beam separation > 10% loss @ min beam separation > 10% loss @ min beam separation Low  quad current 140 sec Beam-beam Simulations - T. Sen

8. Bunch by bunch orbits- 980 GeV From Synchrotron Light Monitor • Calculated from optics model • Pattern for both horizontal and vertical shifts reproduced • Scale of the shifts agree Beam-beam Simulations - T. Sen

9. Bunch by bunch tunes – 980 GeV Calculations “agree” with the measurements of the Pbar tunes Pbar tunes Proton tunes follow the pattern of the Pbar bunch by bunch intensities. Protontunes Beam-beam Simulations - T. Sen

10. Pbar Emittance Growth in Stores “Scallops” Bunch Number Initial Vertical Emittance Store 3554 Vertical Emittance 15 mins later Not observed regularly – very tune dependent Beam-beam Simulations - T. Sen

11. Simulation of Scallops Tunes: 0.580, 0.575 Tunes: 0.585, 0.575 Change in Hor. Emitt. Demonstrates tune dependence Change in Ver. Emitt. A. Valishev - LIFETRAC Beam-beam Simulations - T. Sen

12. Beam Parameters in a Store Pbar Intensities PIntensities P Emittances Pbar Emittances July 16, 2004 – highest luminosity Beam-beam Simulations - T. Sen

13. Dynamic Pbar Lifetimes in Stores Dynamic lifetimes – lifetimes after subtracting losses due to luminosity No obvious symmetry • Lifetimes vary by more than a factor of 20 in some stores • Indicative of beam-beam effects • Not directly related to head-on collisions Approximate3-fold symmetry Beam-beam Simulations - T. Sen

14. Simulations of Lifetimes Simulations with BBSIM • parallelized code • all beam-beam interactions, gas scattering, sextupoles,… • these results assumed uniform beam parameters Pbar bunch1 Demonstrates need for • accurate model of linear optics • accurate values of bunch parameters Beam-beam Simulations - T. Sen

15. Dynamic Proton Lifetime in Stores • Dynamic proton lifetimes • - vary by ~10 times bunch to • bunch • beam-beam effects,IBS • comparable to Pbar dynamic • lifetimes Approximate3-fold symmetry Beam-beam Simulations - T. Sen

16. Proton Losses During Stores • Proton losses well anti-correlated • with Pbar vertical emittance • Similar observations at • SPS (Cornelis, Meddahi & Schmidt) • - HERA (Brinkmann & Willeke) Proton losses not correlated with Pbar intensity - not well understood P. Lebrun Beam-beam Simulations - T. Sen

17. Longitudinal Diffusion – 980 GeV STORE 3725 Protons – diffusion fills the bucket Pbars – sharp edge at 4eV-sec due to protons ? A. Tollestrup Beam-beam Simulations - T. Sen

18. Tevatron: Measurements/Simulations Beam-beam Simulations - T. Sen

19. Tevatron – Simulations w/o Measurements • Tune footprints, bunch by bunch, at 150 GeV and 980 GeV • Dynamic aperture at 980 GeV - dependence on head-on, long-range - dependence on intensities, emittances Beam-beam Simulations - T. Sen

20. RHIC – Coherent Modes Impact of a tune split > ξ Observations of coherent modes Measured J. Qiang – BeamBeam3D Modes decohere rapidly due to chromaticity & other sources. Coherent modes have not degraded machine performance so far. M. Vogt et al. – WDeMo2C 1 Head-on collision ξ= 0.003 Observed υ(σ) – υ(π) = 1.3ξ Beam-beam Simulations - T. Sen

21. LHC Simulations • Dynamic aperture due to beam-beam interactions and magnet field errors • Orbits and tunes along the bunch trains • Choice of the crossing planes • Beam-beam compensation with wires • Ground motion • Synchro-betatron resonances • Halo generation • Possible loss of Landau damping and its restoration • Alternative paths towards higher luminosity • Impact of luminosity monitor on emittance F. Zimmermann ICFA Newsletter Beam-beam Simulations - T. Sen

22. LHC – diffusion due to BB F. Zimmermann - WSDIFF Diffusive aperture with nominal and commissioning beams Scaling law of DDA with bunch intensity. Choice of crossing planes Alternate planes not preferred? Beam-beam Simulations - T. Sen

23. LHC – Wire Compensation BBSIM SPS wire expt, July 2004 WSDIFF results “Agreement” on alignment tolerance Beam-beam Simulations - T. Sen

24. LHC – Strong-strong simulations Impact of crossing angle on the π mode Impact of beam sweeping on emittance growth - less than 0.1% after 1M turns 0 μrad Beam 1 Beam 2 100 μrad Relative Emittance 300 μrad Turns J. Qiang – Beambeam3D W.Herr and F.Jones - BEAMX Beam-beam Simulations - T. Sen

25. Lessons Learnt • Beam-beam performance in hadron colliders cannot be characterized by the beam-beam tune shift alone Tevatron: smoothness of helix, chromaticity, tunes, matched emittances,… • Important to know the linear optics accurately • Simulations are not yet the “real thing” Critical test: qualitative agreement between measured and simulated bunch by bunch lifetimes and emittances • Prepare for the unexpected Beam-beam Simulations - T. Sen

26. Inspiration from Astrophysics Propagation of a jet leading to a Gamma Ray Burst Large scale simulations of the Universe with Cold Dark Matter Zhang, Woosley and Heger Virgo Consortium Beam-beam Simulations - T. Sen

27. Backups Beam-beam Simulations - T. Sen

28. Tevatron Run II Beam-beam Simulations - T. Sen

29. Luminosity vs. Helix Size Luminosity and lifetime vs. helix size Beam-beam Simulations - T. Sen

30. BBSIM Features • Parallel tracking software using MPI • Designed and developed for large particle-turn tracking. (enables 1012 particle-turn tracking) • Includes • Long range Beam-Beam interaction. • Head-on Beam-Beam interaction. • Wire compensation. • RF cavity. • Sextupoles • Mimics Gas scattering Outputs - Lifetime with variable physical aperture - Emittance growth - Diffusion coefficients - Beam profiles - Tune footprints and distribution Beam-beam Simulations - T. Sen

31. Proton Losses – bunch by bunch Beam-beam Simulations - T. Sen

32. HERA Observations Observations ξ(e+) > ξ(p) Changing β* changes the e+ tunes If e+ beam close to a low order resonance, blows up proton beam i.e “weak” beam acts on “strong” beam Physical Mechanisms - Coherent transverse e+ oscillations drive coherent p oscillations ? - Longitudinal e+ oscillations and SBRs couple to p emittance growth ? β* [m] J.Shi et al. 4D PIC style code Beam-beam Simulations - T. Sen