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MEIC Accelerator Design

MEIC Accelerator Design. Yuhong Zhang MEIC Ion Complex Design Workshop Jan. 27 & 28, 2011. Outline. Introduction Luminosity Concept and Design Choices Machine Design Status Ion Complex Summary. Introduction. Future Nuclear Science Program at JLab.

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MEIC Accelerator Design

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  1. MEIC Accelerator Design Yuhong Zhang MEIC Ion Complex Design Workshop Jan. 27 & 28, 2011

  2. Outline • Introduction • Luminosity Concept and Design Choices • Machine Design Status • Ion Complex • Summary

  3. Introduction

  4. Future Nuclear Science Program at JLab • JLab has been developing a preliminary design of an EIC based on the CEBAF recirculating SRF linac for nearly a decade • Requirements of the future nuclear science program drives JLab EIC design efforts to focus on achieving • ultra high luminosity per detector (up to 1035) in multiple detectors • very high polarization (>80%) for both electrons & light ions • Over the last 12 months, we have made significant progress on design optimization • The primary focus is on a Medium-energy Electron Ion Collider ( ) as the best compromise between science, technology and project cost • Energy range is up to 60 GeV ions and 11 GeV electrons • A well-defined upgrade capability to higher energies is maintained • High luminosity & high polarization continue to be the design drivers

  5. Accelerator R&D EICAC Recommendations EICAC Report, Feb. 2010 • Highest priority • Design of JLab EIC • High current (e.g. 50 mA) polarized electron gun • Demonstration of high energy – high current recirculation ERL • Beam-beam simulations for EIC • Polarized 3He production and acceleration • Coherent electron cooling • High priority, but could wait until decision made • Compact loop magnets • Electron cooling for JLab concepts • Traveling focusing scheme (it is not clear what the loss in performance would be if it doesn’t work; it is not a show stopper if it doesn’t) • Development of eRHIC-type SRF cavities • Medium priority • Crab cavities • ERL technology development at JLab

  6. Short Term Design “Contract” & Technical Strategy • The accelerator team is committed to produce a complete MEIC design with sufficient technical details according to recommendations of EICAC • The short term design “contract” for an EIC with the following features • CM energy up to 51 GeV: up to 11 GeV electron, 60(30) GeV proton (ion) • Upgrade option to high energy • 3 IPs, at least 2 of them are available for medium energy collisions • One full acceptance detector, the other detector can be optimized for high luminosity with a large acceptance • Luminosity up to 1034 cm-2s-1per collision point • High polarization for both electron and light ion beams This “contract” will be renewed every 6 to 12 months with major revision • We are taking a conservative technical position by limiting many MEIC design parameters within or close to the present state-of-art in order to minimize technical uncertainty • Maximum peak field of ion superconducting dipole is 6 T • Maximum synchrotron radiation power density is 20 kW/m • Maximum betatron value at FF quad is 2.5 km

  7. Highlights of Last Twelve Months of MEIC Design Activities • Continuing design optimization • Tuning main machine parameters to serve better the science program • Now aim for high luminosity AND large detector acceptance • Simplified design and reduced R&D requirements • Focused on detailed design of major components • Completed baseline design of two collider rings • Completed 1st design of Figure-8 pre-booster • Completed beam polarization scheme with universal electron spin rotators • Updated IR optics design • Continued work on critical R&D • Beam-beam simulations • Nonlinear beam dynamics and instabilities • Chromatic corrections

  8. Luminosity Concept and Design Choices

  9. B-Factories As Role Models PEPII & KEKB • Highly asymmetric lepton-lepton colliders (energies and beam currents) • Pioneered a class of new technologies (crab crossing with crab cavities, etc.) • Highly succeed interaction region design • The present world record of high luminosity, already above2x1034/cm2/s Super-B and SuperKEKB • Upgrades are planed and accelerator R&D are currently underway • Aiming for luminosity above 1036/cm2/s • More technology innovations, most importantly, crab-waist scheme for interaction region

  10. Comparison between e+e- Collider & Traditional Hadron-Hadron Colliders Key factors for high luminosities in B-factories • Very high bunch repetition (~ 500 MHz), thus very large number of bunches • Very small β* (~6 mm) to reach very small spot sizes at collision points • Very short bunch (σz~β*) to avoid luminosity loss due to hour-glass effect • Small bunch charge (~5x109) for making very short bunch possible • High bunch repetition restores high average beam current and luminosity

  11. Collider Luminosity & Beam-Beam Tune-shift • The beam-beam tune-shift • The luminosity can be rewritten as • High beam-beam tune-shift means high luminosity • However, achievable beam-beam tune-shifts are limited by many factors, such as nonlinear b-b forces, nonlinear dynamics in the storage rings, etc • Typical achieved maximum values of beam-beam tune-shift • Electron ~ 0.15 • Proton ~ 0.03 to 0.04 • Luminosity of a collider with head-on collisions is assuming colliding bunches are short, and their spot sizes are matched at collision points. • Presumably, a higher luminosity could be achieved with • High collision frequency • High bunch charges • Small spot sizes at collision points • These parameters are usually limited by collective beam effects. The most important one is beam-beam effect

  12. Optimization of Collider Luminosity • Route for high luminosities • Highest allowable beam-beam tune-shifts (in y-direction for flat beam) • limited by nonlinear beam-beam forces and others • Highest allowable beam current (bunch charge x repetition rate) • electron current limited by synchrotron radiation • proton current limited by space charge tune-shifts and many others • Smallest beta star • limited by bunch length (hour-glass effect) • Unless special IR designs (traveling focusing, crab waist) • High beam current considerations • High bunch charge/low frequency vs. low bunch charge/high frequency Large bunch charge is unfavorable to single bunch instabilities, space charge tune-shift, and small beta-star • High aspect rate make interaction region design much easier

  13. MEIC Design Choice • A great opportunity at JLab • Electron beam: 12 GeV CEBAF delivers a high repetition (up to 1.5 GHz) high polarized CW beam, can be used as a full energy injector • Proton/ion beam: a new green-field ion complex, can be specially designed to match ion beams to the electron beam  We should be able to duplicate the great success of e+e- colliders in the EIC! • MEIC colliding ion beams comparing to eRHIC • High bunch repetition rate, up to 1.5 GHz  115 times higher • Small proton bunch charge, a few of 109,  57 times smaller • Short bunch length, down to 1 cm,  5 times smaller • Small linear charge density  7 times smaller • Small beta-star, same to bunch length  25 times smaller

  14. Why Linac(ERL)-Ring is Not Good for MEIC? • Advantage of an linac-ring collider electron beam can tolerate much larger beam-beam disruption, therefore, one can achieve a high luminosity in principle. • Reducing proton spot sizes (emittances) Needs strong cooling, could be very difficult to achieve • Increasing proton bunch charge Single bunch effects such as space charge tune shift could get much worse • Longer bunch length High charge density may be mitigated by increasing the bunch length, Beta-star has to be increase to avoid the hour-glass effect, Large beta-star reduce some of the luminosity gain of the linac-ring approach. • The linac-ring approach could provide some advantages, especially for traditional regime of collider design, when bunch is long anyway, and beam current is low, therefore increasing of proton bunch charge is possible. However, a very strong cooling is required. That is not MEIC.

  15. Technical Challenges for ERL-Ring Design • The JLab EIC design started with an ERL-Ring collider initially. • It is a natural approach since JLab already has a CEBAF recirculated linac, and is also a world leader in ERL technology • We had recognized the high current polarized electron sources issue, about 2000 times beyond start-of-art, associated to a ERL-ring design approach. • A circulator-ring had been suggested to the ERL-Ring design of ELIC to reduce the electron current from polarized gun by a factor of 100. However, the remaining electron source R&D is still challenging • JLab eventually abandoned the circulator-ring based ERL-ring approach for MEIC because • It requires a significant R&D on polarized electron source • It requires development of high-energy, high-current, multiple-pass ERL and circulator ring technologies • It requires a proof of new (linac-ring) collider concept • It doesn’t provide a significant increase of luminosity for MEIC design parameter regime

  16. Current MEIC Design

  17. MEIC Design Goals • Energy Wide CM energy range between 10 GeV and 100 GeV • Low energy: 3 to 10 GeV e on 3 to 12 GeV/c p (and ion) • Medium energy: up to 11 GeV e on 60 GeV p or 30 GeV/n ionand for future upgrade • High energy: up to 10 GeV e on 250 GeV p or 100 GeV/n ion • Luminosity • 1033 up to 1035 cm-2 s-1per collision point • Multiple interaction points • Ion Species • Polarized H, D, 3He, possibly Li • Up to heavy ion A = 208, all stripped • Polarization • Longitudinal at the IP for both beams, transverse of ions • Spin-flip of both beams • All polarizations >70% desirable • Positron Beamdesirable

  18. MEIC : Medium Energy EIC • Three compact rings: • 3 to 11 GeV electron • Up to 12 GeV/c proton (warm) • Up to 60 GeV/c proton (cold)

  19. MEIC : Detailed Layout warm ring cold ring

  20. ELIC: High Energy & Staging Straight section Serves as a large booster to the full energy collider ring Arc

  21. MEIC Design Parameters For a Full-Acceptance Detector

  22. MEIC Design Parameters For a High-Luminosity Detector

  23. MEIC & ELIC: Luminosity Vs. CM Energy https://eic.jlab.org/wiki/index.php/Machine_designs

  24. MEIC Ring-Ring Design Features • Ultra high luminosity • Polarized electrons and polarized light ions • Up to 3 IPs (detectors) for high science productivity • “Figure-8” ion and lepton storage rings • Ensures spin preservation and ease of spin manipulation • Avoids energy-dependent spin sensitivity for all species • Present CEBAF injector meets MEIC requirements • 12 GeV CEBAF can serve as a full energy injector • Simultaneous operation of collider & CEBAF fixed target program possible • Experiments with polarized positron beam would be possible

  25. Figure-8 Ion Rings • Figure-8 optimum for polarized ion beams • Simple solution to preserve full ion polarization by avoiding spin resonances during acceleration • Energy independence of spin tune • g-2 is small for deuterons; a figure-8 ring is the only practical way to arrange for longitudinal spin polarization at interaction point • No technical disadvantages • Only disadvantage is small cost increase

  26. MEIC Ion Beams & Ion Complex

  27. Design Goal of MEIC Ion Complex • Developing a conceptual design for a technical sound and cost effective ion complex for the MEIC project • The MEIC ion complex should be able to deliver a required colliding ion beam for a successful operation of a medium energy EIC • Polarized light ions (>75% in the collider) & un-polarized heavy ions • Colliding beam current up to 1 A (~5x109 protons/bunch) • Compatible with a bunch repetition frequency of 750 MHz • Capable of being upgraded to 1.5 GHz • RMS bunch length of 5 to 10 mm for colliding beams • Emittance at injection of <5 mm-mrad • Round beams at injection • Compatible with a luminosity lifetime of ~10 hours Highly polarized light ions and un-polarized heavy ions

  28. Difference Between B-factories & MEIC • Leptons and ion beams are still quite different • Lepton beams have (radiation) damping, ion beams don’t issue: achieving & preserving the beam quality • Leptons beams have full energy injection, ion beams don’t issue: how to form a high intensity short bunch ion beam • B-factories and EIC are also different • Distance between the final focusing magnets and a collision point in EIC is much larger than the B-factories, so chromaticity is huge. Staged electron cooling SRF Linac, electron cooling during accumulation Chromatic compensation

  29. cooling Cooling (for accumulation) Large booster-Low energy collider ring source SRF Linac Pre-booster-Accumulator ring Cooling (for collision beam) Medium energy collider ring MEIC Ion Complex As We Envisioned

  30. Electron Cooling of Colliding Ion Beams Solenoid (7.5 m) 10 m injector SRF ERL dumper • Electron cooler is located at center for figure-8 ring • Compact cooler design • Doubled length of cooling section, therefore the cooling rate • Reduces number of circulation

  31. MEIC Study Group A. Afanasev, S. Ahmed, A. Bogacz, J. Benesch, P. Brindza, A. Bruell, L. Cardman, J. Chen, Y. Chao, S. Chattopadhyay, E. Chudakov, P. Degtiarenko, J. Delayen, Ya. Derbenev, R. Ent, P. Evtushenko, A. Freyberger, D. Gaskell, J. Grames, L. Harwood, T. Horn, A. Hutton, C. Hyde, R. Kazimi, F. Klein, G. A. Krafft, R. Li, F. Marhauser, L. Merminga, V. Morozov, J. Musson, P. Nadel-Turonski, F. Pilat, M. Poelker, R. Rimmer, T. Satogata, M. Spata, B. Terzic, M. Tiefenback, A. Thomas, H. Wang, C. Weiss, B. Wojtsekhowski, B. Yunn, Y. Zhang - Jefferson Laboratory staff and users W. Fischer, C. Montag - Brookhaven National Laboratory M. Sullivan - SLAC D. Barber - DESY V. Danilov - Oak Ridge National Laboratory V. Dudnikov - Brookhaven Technology Group P. Ostroumov, S. Manshikonda - Argonne National Laboratory B. Erdelyi - Northern Illinois University and Argonne National Laboratory H. Sayed – Old Domino University

  32. Backup Slides

  33. Summary • MEIC is optimized to collide a wide variety of polarized light ions and unpolarized heavy ions with polarized electrons (or positrons) • MEIC covers an energy range matched to the science program proposed by the JLab nuclear physics community (~4200 GeV2) with luminosity up to 3x1034 cm-2s-1 • An upgrade path to higher energies (250x10 GeV2), has been developed which should provide luminosity of close to 1035 cm-2s-1 • The design is based on a Figure-8 ring for optimum polarization, and an ion beam with high repetition rate, small emittance and short bunch length • Electron cooling is absolutely essential for cooling & bunching the ion beam • We have identified the critical accelerator R&D topics for MEIC, and are presently working on them • Our present MEIC design is mature and flexible, able to accommodate revisions in design specifications and advances in accelerator R&D MEIC is the future of Nuclear Physics at Jefferson Lab

  34. Collaborations Established • Interaction region design M. Sullivan (SLAC) • ELIC ion complex front end P. Ostroumov (ANL) (From source up to injection into collider ring) • Ion source V. Dudnikov, R. Johnson (Muons, Inc) V. Danilov (ORNL) • SRF Linac P. Ostroumov (ANL), B. Erdelyi (NIU) • Chromatic compensation A. Netepenko (Fermilab) • Beam-beam simulation J. Qiang (LBNL) • Electron cooling simulation D. Bruhwiler (Tech X) • Electron spin tracking D. Barber (DESY)

  35. Future Accelerator R&D We will concentrate R&D efforts on the most critical tasks Focal Point 1: Complete Electron and Ion Ring designs Sub tasks: Finalize chromaticity correction of electron ring and complete particle tracking Insert interaction region optics in ion ring Start chromaticity correction of ion ring, followed by particle tracking Focal Point 2: IR design and feasibility studies of advanced IR schemes Sub tasks: Develop a complete IR design Beam dynamics with crab crossing Traveling final focusing and/or crab waist?

  36. Future Accelerator R&D Focal Point 3: Forming high-intensity short-bunch ion beams & cooling Sub tasks: Ion bunch dynamics and space charge effects (simulations) Electron cooling dynamics (simulations) Dynamics of cooling electron bunch in ERL circulator ring Led by Peter Ostroumov (ANL) Focal Point 4: Beam-beam interaction Sub tasks: Include crab crossing and/or space charge Include multiple bunches and interaction points Additional design and R&D studies: Electron spin tracking, ion source development Transfer line design

  37. MEIC Luminosity: 1 km Ring, 8 Tesla Assuming maximum peak field of ion magnet 8 Tesla, highest proton energy can be 96 GeV Large acceptance High luminosity

  38. The second option is using 1 km medium-energy ion ring for higher proton beam current at 30 GeV protons for lowering the space charge tune-shift ELIC Luminosity: 2.5 km Ring, 8 Tesla Large acceptance High luminosity

  39. MEIC Adopts Proven Luminosity Approaches High luminosity at B factories comes from: • Very small β* (~6 mm) to reach very small spot sizes at collision points • Very short bunch length (σz~ β*) to avoid hour-glass effect • Very small bunch charge which makes very short bunch possible • High bunch repetition rate restores high average current and luminosity • Synchrotron radiation damping  KEK-B and PEPII already over21034cm-2 s-1 JLab believes these ideas should be replicated in the next electron-ion collider ( ): high-luminosity detector

  40. MEIC Design Details • Our design is mature, having addressed (in various degrees of detail) the following important aspects of MEIC: • Electron and ion beam optics • Electron cooling • ERL circulator cooler • Electron polarization, universal spin rotator • Beam synchronization • Electron beam time structure & RF system • IR design and optics • Beam-beam simulations • Tracking and dynamical aperture • Beam stability • Forming the high-intensity ion beam: ion SRF linac, ion pre-booster • Synchrotron radiation background • Detector design

  41. Figure-8 Electron Collider Ring

  42. MEIC: Reaching Down To Low Energy electron ring (1 km ) A compact (~150 m) ring dedicated to low energy ion low energy IP Compact low energy ion ring Medium energy IP • Space charge effect is the leading factor for limiting ion beam current and luminosity • A small ring with one IP, two snake, injection/ejection and RF • Ion energy range from 12 GeV to 20 GeV • Increasing ion current by a factor of 6, thus luminosity by 600%

  43. Electron Collider Ring • Electron ring is designed in a modular way • two long (240 m) straights (for two IPs) • two short (20 m) straights (for RF module), dispersion free • four identical (120º) quarter arcs, made of 135º phase advance FODO cell with dispersion suppressing • four 50 m long electron spin rotator blocks One quarter arc 135º FODO Cell for arc 2 dis. sup. cells 2 dis. sup. cells 26 FODO cells circumference ~1000 m phase adv/cell: 1350

  44. Electron Polarization in Figure-8 Ring electron spin in vertical direction ions electron electron spin in vertical direction Universal Spin Rotators electron spin in longitudinal direction Self polarization time in MEIC spin tuning solenoid • Polarized electron beam is injected at full energy from 12 GeV CEBAF • Electron spin is in vertical direction in the figure-8 ring, taking advantage of self-polarization effect • Spin rotators will rotate spin to longitudinal direction for collision at IP, than back to vertical direction in the other half of the ring

  45. Universal Spin Rotator e- spin from arc spin 8.8º BL = 28.712 Tesla m 4.4º solenoid 4.16 m solenoid 4.16 m decoupling quad insert C 0 M = - C 0

  46. Electron Beam Time Structure & RF System <3.3 ps (<1 mm) 0.2 pC From CEBAF SRF Linac 0.67 ns (20 cm) 1.5 GHz Microscopic bunch duty factor 5x10-3 10-turn injection 33.3μs (2 pC) 40 ms (~5 damping times) 25 Hz 3000 “pulses” =120 s

  47. Possible Electron Ring RF Systems CESR PEP II BESSY RF may prefer 748.5 MHz (coupler limits)

  48. Beam Synchronization Electron speed is already speed of light at 3 to 11 GeV, ion speed is not, there is 0.3% variation of ion speed from 20 to 60 GeV Needs over 67 cm path length change for a 1000 m ring Solution for case of two IPs on two separate straights At the higher energies (close to 60 GeV), change ion path length  ion arc on movers At the lower energies (close to 20 GeV), change bunch harmonic number  Varying number of ion bunches in the ring With two IPs in a same straights Cross-phasing More studies/implementation scheme needed Harmonic Number vs. Proton Energy eRHIC e-Ring Path Length Adjustment (eRHIC Ring-Ring Design Report)

  49. Ion SRF Linac (First Cut) QWR HWR DSR • Accelerating a wide variety of polarized light ions and unpolarized heavy ion • Up to 285 MeV for H- or 100 MeV/u for 208Pb+67 • Requires stripper for heavy ions (Lead) for efficiency optimization

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