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Summary of the Working Group on Electron-Positron Circular Colliders (M2)

Summary of the Working Group on Electron-Positron Circular Colliders (M2). Stuart Henderson Spallation Neutron Source Convenors: S. Henderson (SNS), K. Oide (KEK), J. Seeman (SLAC). Working Group Participants.

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Summary of the Working Group on Electron-Positron Circular Colliders (M2)

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  1. Summary of the Working Group on Electron-Positron Circular Colliders (M2) Stuart Henderson Spallation Neutron Source Convenors: S. Henderson (SNS), K. Oide (KEK), J. Seeman (SLAC) Electron-Positron Circular Collider Working Group – S. Henderson

  2. Working Group Participants M. Sullivan, C. Biscari, K. Oide, S. Henderson, M. Tigner, J. Seeman, U. Wienands, S. Ecklund, A. Fisher, D. Sagan, F.J. Decker, R. Assmann, T. Sen, A. Skrinsky, D. Rubin, P. Colestock, J. Norem, Y. Cai, G. Hoffstaetter, A. Burov, H. Yamamoto, M. Sokoloff, A. Bogacz, Y. Derbenev, S.Y. Lee, A. Chao, M. Palmer, J. Rogers, J. Shi, J. Ellison, Y. Ohnishi, M. Liepe, A. Hutton, K. Hubner, …. Electron-Positron Circular Collider Working Group – S. Henderson

  3. Working Group Charge 1) “…perform a survey of the present status as well as future promises of e+e- circular colliders.” 2) “…emphasis on clear identification of the beam physics and accelerator technology limits…” 3) “…identify new and promising ideas even though they may need additional work.” 4) “…summarize the highest priority research topics…” Electron-Positron Circular Collider Working Group – S. Henderson

  4. Electron-Positron Collider Landscape VLLC LEP CESR CESR-C Super-B-Factory PEP-II 1035 PEP-II KEK-B Super-KEK-B VEPP-5 BEPC BEPC-II VEPP-4M DAFNE VEPP-2M VEPP-2000 PEP-N Future Past Present Electron-Positron Circular Collider Working Group – S. Henderson

  5. Performance Issues: e- cloud Instability (e+ LER) Effects: e+ beam blowup with I rapid pressure with I  increase along train lum reduction along train Mitigation: TiN coated vac chamber wind solenoids (800m) tailor bunch pattern HOM heating in Vertex beampipe Orbit/Dispersion/Coupling PEP-II Status Electron-Positron Circular Collider Working Group – S. Henderson

  6. PEP-II Plans • 2x1034: More RF, more solenoids (ECI), optimize working point, improved IP chambers, better feedback kickers • 1x1035: More RF, IR upgrade: reduced *, l with IR quad modifications, crossing-angle, vac chamber upgrades for HOM reduction. Electron-Positron Circular Collider Working Group – S. Henderson

  7. Performance Issues: ECI: 1300m of solenoid Operating point at CESR tunes (qh=0.51, qv=0.58) Good beta/coupling correction Movable masks heating from HOM Heating of IR chambers KEK-B Status Electron-Positron Circular Collider Working Group – S. Henderson

  8. KEK-B Plans • 1x1034: more solenoids, 2 bunch e+ injection, IR vac chamber replacement, param search • 1x1035:Super KEK-B: Exchange e+/e-, upgrade injector, antechamber vac system, SR absorbers, Crab cavity, More RF, HOM Dampers Electron-Positron Circular Collider Working Group – S. Henderson

  9. Performance Issues: CESR operated in “Factory Mode” since Nov. 2000 Injection improvements Shortened run length “Pedal to the Metal” Continue to push the limits of single-ring collider approach Beam-beam tuneshift increased x2 in 9 yrs Confronting Long-range parasitic B-B effects Vertical separation at IP Differential H, V tunes CESR Status Electron-Positron Circular Collider Working Group – S. Henderson

  10. Extend operating range of CESR to 1.55 < E < 5.6 GeV with damping wigglers Luminosity scaling: Assume limiting Ib E Assume v  1/1/3 Issues: Reduced *:Superconducting Quad IR installation in progress Combat parasitic beam-beam with bunch-by-bunch orbit and tune adjustments Wiggler nonlinearities Beam stability, lifetimes and backgrounds look fine. CESR Plans: CESR-C Electron-Positron Circular Collider Working Group – S. Henderson

  11. Performance Issues: Strong Solenoid Coupling (40 rotation) achieved 0.2% coupling (1% design) Nonlinearities in wigglers, sextupoles, correctors Touschek limits lifetime: top-up operation 2nd IR -> chromaticity – strong sextupoles Plans: reduce coupling, detune 2nd IP, working point, octupole compensation, work up current DAFNE Status and Plans Electron-Positron Circular Collider Working Group – S. Henderson

  12. Recent Successes Think about what has been accomplished! • > 1 Amp beams can be stored • Bunch-by-bunch transverse and longitudinal feedback controls coupled-bunch instabilities • RF systems can handle large beam-loading • Asymmetric energy collisions work (energy transparency requirement is weak) • Higher than expected beam-beam tuneshifts • Detectors can handle beam backgrounds • Large crossing-angles are OK • PEP-II has reached design luminosity, KEK-B within a factor of 2 e+e- colliders can reach design luminosity in a reasonable time in the original machine configuration Electron-Positron Circular Collider Working Group – S. Henderson

  13. BINP Plans • VEPP-4M: in operation at (1-6 GeV) • Expect L=2x1031 at 5 GeV (higher with more wigglers) • Present operation at +- • VEPP-2000: (replacing VEPP-2M) is being constructed at BINP. • Ecm = 1-2 GeV, Lum = 1032 /cm2/s • High  from round colliding beams. • VEPP-5: tau/charm collider • L = 1034/cm2/swith round beams • Injector complex is constructed Electron-Positron Circular Collider Working Group – S. Henderson

  14. PEP-N Collider • Collide PEP-II e+ LER with100-800 MeV e-: • Linac • Storage ring • Linac with energy-recovery • Ecm= 1-3 GeV. • Beam-beam tuneshift low so that LER unaffected • L = 2x1031 /cm2/s at E= 800 MeV. • IR Separation with large dipole field at IP Electron-Positron Circular Collider Working Group – S. Henderson

  15. Outfit VLHC tunnel with 90<ECM<400 GeV e+e- collider Conservative extrapolation of LEP technology Use Nb/Cu LEP cavities Considering Z-factory injector for VLLC Many issues: TMCI at injection Arcs (one or two rings) Achievable polarization Low field Cost e+e- Collider in the VLHC Tunnel Electron-Positron Circular Collider Working Group – S. Henderson

  16. J. Seeman has put forth parameters for a 1036 Super-B-Factory Beyond the upgrade path of existing B-factories. A new machine based on new technologies is required. Every parameter pushed to limit: many accelerator physics and technology issues (more later) Great launching point! 1036 Super-B-Factory Electron-Positron Circular Collider Working Group – S. Henderson

  17. R&D Issues for Operating Colliders • All machines struggling with • Coupling correction (solenoid compensation) • Bunch-by-bunch effects (orbit, tunes, beamsize) • Day-to-day and hour-to-hour drifts in orbit/coupling/dispersion that affect luminosity • Need real-time monitoring/correction of fundamental optics parameters: • Our diagnostics and corrections are not up to the task! • Getting a handle on these effects will allow true factory operation, and free up much needed personpower. Electron-Positron Circular Collider Working Group – S. Henderson

  18. R&D for Future Machines • Increasing I: Present 1.5 A to 20A • What does the vacuum system look like? Requires low-impedance welded no-bellows chambers (need to keep temp constant) Can the SR power be brought outside? (natural for VLLC) Chamber materials and SR absorber geometries • RF systems: Large RF plants, higher impedance and instability growth rates, very high beam loading • Feedback systems: Does scale-up of existing systems work? Need higher-power and bandwidth and lower impedance transducers • Machine Protection • Combat ECI – solenoids are partial cure – other cures needed Electron-Positron Circular Collider Working Group – S. Henderson

  19. R&D for Future Machines • Reducing * • Stronger quads closer to IP (CESR:40cm) • IR Chromaticity k stronger sext dynamic aperture • Bunch length must follow to avoid hourglass: • Increase RF voltage • Low-momentum compaction optics (need real tests of low- optics in a colliding beam machine) • Short-bunch limitations (Ohmic heating of vac chamber, Coherent SR). Looks ok at 2mm, bunch lengthening? • Intrabeam scattering? • HOM loss in RF, feedback kickers, crotches Electron-Positron Circular Collider Working Group – S. Henderson

  20. R&D for Future Machines • Increase beam-beam tuneshift parameter • We don’t understand what sets limits: • Experience at CESR shows “clean-living” and active parameter exploration increased v x2 in 9 years • Experience at LEP shows strong dependence on damping • Can the B-B tunespread be tailored favorably with beam-beam compensation methods? • Round Beam collisions at CESR demonstrated v = 0.09. Can we harness for real luminosity production? Important tests at CESR and VEPP-2000 • We seem to be entering a new era in strong-strong B-B simulations. We have the opportunity to learn! Electron-Positron Circular Collider Working Group – S. Henderson

  21. R&D for Future Machines • Interaction Region Issues • Separation Issues: crossing-angles, parasitic crossings • Real Estate: Quads closer to IP, smaller vertex beampipes • Detector backgrounds: (lost-particle and SR, injection, luminosity) Detector technology must develop to handle radiation levels and occupancy • Impact of short beam lifetime and continuous injection on detector • Can SR from round beams be shielded? • Heating, HOM (Be beampipe ok). We need reliable HOM calculational tools Electron-Positron Circular Collider Working Group – S. Henderson

  22. Summary and Outlook • Tremendous progress has been made in e+e- collider design, engineering and performance in recent years • Luminosity is being delivered at unprecedented rates • The demonstrated success of e+e- factories gives confidence that higher luminosities can be achieved over a wide range in energies. • Much R&D to be done ranging from engineering for high power deposition to fundamental beam dynamics to computational physics Electron-Positron Circular Collider Working Group – S. Henderson

  23. Performance of the Factories Electron-Positron Circular Collider Working Group – S. Henderson

  24. Outline • WG Charge (1) • E+e- collider landscape (1) • Status of the operating e+e- colliders (11) • PEP-II (status and upgrades) (2) • Status (Lum, I, Optics…) • Performance Issues (e- cloud, lum vs. bunch…) • Upgrade plans (10^35 upgrade plan) • KEK-B (status and upgrades; super KEK-B) (2) • CESR (status and upgrades) (2) • DAFNE (status) (2) • BEPC (status and upgrades) (…2…) • VEPP-2M and VEPP-4 • LEP • Summary of Present Status (1) • Perspective/Outlook (1) • New Machines (4) • Upgrades • VEPP-2000, PEP-N • Super-B-factory • VLLC • Electron-Positron Collider Issues and Research (4) • IR Issues • Beam-beam interaction • Very high current beams • Fundamental accelerator physics problems • Perspective and Summary (1) Electron-Positron Circular Collider Working Group – S. Henderson

  25. “…perform a survey of the present status…” • DAFNE L = 3.2x1031 cm-2 sec-1 (design 1x1032) Progress in understanding coupling/solenoid compensation and non-linearities • CESR L=1.3x1033 cm-2 sec-1 Pushing limit of single-ring collider with 45 bunches/beam. Confronting limitations of parasitic beam-beam • PEP-II L=3.3x1033 cm-2 sec-1 (design 3.0x1033) 4.1 fb-1/month Overcoming e- cloud effect with solenoid • KEK-B L=4.4x1033 cm-2 sec-1 (design 1.0x1034) Higher currents, more solenoids for e- cloud, working point Electron-Positron Circular Collider Working Group – S. Henderson

  26. “…vision of the future promises of e+e- colliders…” • Upgrades of existing facilities: KEK-B: PEP-II: CESR: (BEPC – not represented) • New Machines: PEP-N: VLLC: VEPP-2000: 1036 B-factory Electron-Positron Circular Collider Working Group – S. Henderson

  27. “…perform a survey of the present status…..” • New factories are performing very well. • Rapid turn-on and luminosity ramp-up sets a new standard in performance • 2: “….the vision of the future promises….” • Upgrade paths for PEP-II and KEK-B are relatively straightforward: • Higher Current • CESR-B: • PEP-N: • VLLC: • VEPP-2000: Electron-Positron Circular Collider Working Group – S. Henderson

  28. “…identification of beam physics and technology limits…” • Single-ring Colliders: Destructive parasitic beam-beam effects • Two-ring colliders: E- cloud mitigation • All colliders: Solenoid compensation and coupling in e+e- colliders (diagnostics and understanding) Lacking diagnostics: Operational Issues Orbit drift from thermal effects Understanding beams at IP Achieving design lattice.. IR issues at high-current rings: Detector interface, SR and HOM heating, beam separation, strong quads near IP Electron-Positron Circular Collider Working Group – S. Henderson

  29. “Identify new and promising ideas” • Round beams (not new but promising) Important tests at VEPP-2000 and CESR are forthcoming • High-current storage ring design: No weld - no bellows chambers to minimize impedance Absorb SR power outside vac chamber (natural for VLLC, thin windows required for B-factory) • Very short bunches (1-2mm) Need to understand limits from vacuum chamber, Coherent SR, bunch lengthening effects • Short lifetime, continuous filling operation of a collider Electron-Positron Circular Collider Working Group – S. Henderson

  30. Electron-Positron Circular Collider Working Group SummaryStuart HendersonSpallation Neutron Source • Where we are: • Can store 1A currents • Can provide beam stability in 3 d.o.f. with feedback systems • Can compensate large beam-loading • Can achieve high tuneshift parameters 0.06-0.07at B-factory energies • Can bring two high-current beams into collision with acceptable backgrounds • Can achieve L > 4x1033 cm-2 sec-1 and 4.7 fb-1/month • Rapid turn-on and luminosity ramp-up of PEP-II and KEK-B demonstrates that design luminosities can be achieved! • This marks a new era in e+e- collider performance! Electron-Positron Circular Collider Working Group – S. Henderson

  31. Electron-Positron Circular Colliders – Where We’re Going • Machines under consideration range in energy from 1 < s < 400 GeV with luminosities up to 1036 cm-2 sec-1 • Upgrades: • Plans are forming for PEP-II and KEK-B to reach L = 1035 cm-2 sec-1 (Aggressive but achievable) • Plans to extend CESR energy range with wigglers to cover 1.5 < E < 5.6 GeV • New machines: • VLLC (Z-factory, ttbar) • PEP-N (1-3 GeV) • VEPP-2000 (1-2 GeV) • Super-B-factory with L = 1036 cm-2sec-1 and 20A + 5A Electron-Positron Circular Collider Working Group – S. Henderson

  32. Electron-Positron Circular Colliders -How do we get there? A Sampling of R&D issues under discussion: Interaction Region Design Even higher currents (backgrounds, SR and HOM power) Smaller V* (Superconducting Quads inside detector, IR chromaticity) Beam separation (closely spaced bunches) Smaller beampipes High-Current Storage Rings e- cloud mitigation RF systems and very heavy beam-loading Vacuum system design (no-bake / no bellows low-impedance chambers) Limits to bunch length Round Beam Collisions Potential for higher specific luminosity Tests at CESR and VEPP-2000 Electron-Positron Circular Collider Working Group – S. Henderson

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