caf8414c55713f2e0c920eb6153a1976.ppt
- Количество слайдов: 63
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 • 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 ( the best compromise between science, technology and project cost – Energy range is up to 60 Ge. V ions and 11 Ge. V electrons • A well-defined upgrade capability to higher energies is maintained • High luminosity & high polarization continue to be the design drivers ) as
Accelerator R&D EICAC Recommendations • Highest priority – Design of JLab EIC – – – EICAC Report, Feb. 2010 High current (e. g. 50 m. A) polarized electron gun Demonstration of high energy – high current recirculation ERL Beam-beam simulations for EIC Polarized 3 He 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 e. RHIC-type SRF cavities • Medium priority – Crab cavities – ERL technology development at JLab
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 Ge. V: up to 11 Ge. V electron, 60(30) Ge. V 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-2 s-1 per 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 k. W/m • Maximum betatron value at FF quad is 2. 5 km
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 1 st 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
Luminosity Concept and Design Choices
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 above 2 x 1034 /cm 2/s Super-B and Super. KEKB • Upgrades are planed and accelerator R&D are currently underway • Aiming for luminosity above 1036 /cm 2/s • More technology innovations, most importantly, crab-waist scheme for interaction region
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 (~5 x 109) for making very short bunch possible High bunch repetition restores high average beam current and luminosity KEK-B & PEPII Traditional hadron collider A factor of Bunch repetition frequency ~ 500 MHz 5 to 10 MHz 50 Number of bunches in ring > 2000 A few and up to 100 20 to 50 A few of 1011 1/10 0. 5 cm 70 to 100 cm 1/100 0. 5 to 1 cm 30 to 100 cm 1/100 0. 1 0. 025 4 2 x 1034 Up to a few of 1032 50 to 100 Particles per Bunch length Beta-star Beam-beam tune-shift Luminosity per IP
Collider Luminosity & Beam-Beam Tune-shift • 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 • The beam-beam tune-shift • The luminosity can be rewritten as • High beam-beam tune-shift means high luminosity • However, achievable beam-beam tuneshifts 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
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
MEIC Design Choice • A great opportunity at JLab – Electron beam: 12 Ge. V 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 – – – High bunch repetition rate, up to 1. 5 GHz Small proton bunch charge, a few of 109, Short bunch length, down to 1 cm, Small linear charge density Small beta-star, same to bunch length comparing to e. RHIC 115 times higher 57 times smaller 5 times smaller 7 times smaller 25 times smaller
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.
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
Current MEIC Design
MEIC Design Goals § Energy Wide CM energy range between 10 Ge. V and 100 Ge. V • Low energy: 3 to 10 Ge. V e on 3 to 12 Ge. V/c p (and ion) • Medium energy: up to 11 Ge. V e on 60 Ge. V p or 30 Ge. V/n ion and for future upgrade • High energy: up to 10 Ge. V e on 250 Ge. V p or 100 Ge. V/n ion § Luminosity • 1033 up to 1035 cm-2 s-1 per collision point • Multiple interaction points § Ion Species • Polarized H, D, 3 He, 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 Beam desirable
MEIC : Medium Energy EIC Three compact rings: • 3 to 11 Ge. V electron • Up to 12 Ge. V/c proton (warm) • Up to 60 Ge. V/c proton (cold)
MEIC : Detailed Layout warm ring cold ring
ELIC: High Energy & Staging Straight section Serves as a large booster to the full energy collider ring Arc Stage Max. Energy (Ge. V/c) p e Medium 96 11 High 250 20 Ring Size (m) Ring Type IP # p e 1000 Cold Warm 3 2500 Cold Warm 4
MEIC Design Parameters For a Full-Acceptance Detector Proton Electron Beam energy Ge. V 60 5 Collision frequency GHz 0. 75 Particles per bunch 1010 0. 416 2. 5 Beam Current A 0. 5 3 Polarization % >70 ~ 80 Energy spread 10 -4 ~3 7. 1 RMS bunch length mm 10 7. 5 Horizontal emittance, normalized µm rad 0. 35 54 Vertical emittance, normalized µm rad 0. 07 11 Horizontal β* cm 10 10 Vertical β* cm 2 2 Vertical beam-beam tune shift 0. 014 0. 03 Laslett tune shift 0. 07 Very small 7 3. 5 Distance from IP to 1 st FF quad Luminosity per IP, 1033 m cm-2 s-1 5. 6
MEIC Design Parameters For a High-Luminosity Detector Proton Electron Beam energy Ge. V 60 5 Collision frequency GHz 0. 75 Particles per bunch 1010 0. 416 2. 5 Beam Current A 1 3 Polarization % >70 ~ 80 Energy spread 10 -4 ~3 7. 1 RMS bunch length mm 10 7. 5 Horizontal emittance, normalized µm rad 0. 35 54 Vertical emittance, normalized µm rad 0. 07 11 Horizontal β* cm 4 4 Vertical β* cm 0. 8 Vertical beam-beam tune shift 0. 007 0. 03 Laslett tune shift 0. 014 Very small 4. 5 3. 5 Distance from IP to 1 st FF quad Luminosity per IP, 1033 m cm-2 s-1 14. 2 (20)
MEIC & ELIC: Luminosity Vs. CM Energy https: //eic. jlab. org/wiki/index. php/Machine_designs
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 Ge. V 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
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
MEIC Ion Beams & Ion Complex
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 (~5 x 109 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
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 Staged electron cooling – Leptons beams have full energy injection, ion beams don’t issue: how to form a high intensity short bunch ion beam SRF Linac, electron cooling during accumulation • 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. Chromatic compensation
MEIC Ion Complex As We Envisioned Cooling (for accumulation) source SRF Linac Large booster. Low energy collider ring Pre-booster. Accumulator ring Maximum Energy (Ge. V/c) Cooling (for collision beam) Cooling cooling Medium energy collider ring Processes Source/SRF linac 0. 2 Full stripping Prebooster/Accumulator-Ring 3 to 5 DC electron Stacking/accumulating Large booster Low energy ring 12 to 20 Electron (for collision) RF bunching (for collision) Medium energy ring 60 to 100 Electron RF bunching (for collision)
Electron Cooling of Colliding Ion Beams 10 m oid en ) l So. 5 m (7 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 Cooling (Derbenev) longitudinal IBS (Derbenev) s Horizontal IBS (Piwinski) s s 7. 8 86 66 51
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
Backup Slides
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 Ge. V 2) with luminosity up to 3 x 1034 cm-2 s-1 • An upgrade path to higher energies (250 x 10 Ge. V 2), has been developed which should provide luminosity of close to 1035 cm-2 s-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
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 – SRF Linac V. Dudnikov, R. Johnson (Muons, Inc) V. Danilov (ORNL) 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)
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: Sub tasks: IR design and feasibility studies of advanced IR schemes Develop a complete IR design Beam dynamics with crab crossing Traveling final focusing and/or crab waist?
Future Accelerator R&D Focal Point 3: Sub tasks: Forming high-intensity short-bunch ion beams & cooling 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: Sub tasks: Beam-beam interaction 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
MEIC Luminosity: 1 km Ring, 8 Tesla Assuming maximum peak field of ion magnet 8 Tesla, highest proton energy can be 96 Ge. V Large acceptance High luminosity Proton Energy Electron Energy S CM Energy Luminosity (L=7 m, β*=2 cm) Luminosity (L=4. 5 m, β*=8 mm) Ge. V 2 Ge. V 1033 cm-2 s-1 96 3 1152 34. 0 12. 5 30. 4 96 4 1536 39. 2 10. 0 25. 0 96 5 1920 43. 8 6. 6 16. 4 96 6 2340 48. 0 2. 6 6. 6 96 7 2688 51. 9 1. 2 2. 9 96 9 3456 55. 8 0. 3 0. 74 96 11 4224 65. 0 0. 1 0. 2
ELIC Luminosity: 2. 5 km Ring, 8 Tesla Proton Energy Electron Energy s CM Energy Large acceptance Luminosity (L=7 m, β*=2 cm) High luminosity Luminosity (L=4. 5 m, β*=8 mm) Ge. V 2 Ge. V 1033 cm-2 s-1 250 3 3000 54. 8 8. 3 20. 7 250 5 5000 70. 7 18. 5 46. 4 250 6 6000 77. 5 20. 2 50. 5 250 7 7000 83. 7 20. 7 64. 5 250 8 8000 89. 5 18. 9 57. 6 250 9 9000 94. 9 15. 8 39. 6 250 11 11000 104. 9 7. 5 18. 8 250 20 20000 141. 4 3. 1 6. 2 Proton Energy Electron Energy Ring Circumference Luminosity (L=7 m, β*=2 cm) Luminosity (L=4. 5 m, β*=8 mm) Ge. V m 1033 cm-2 s-1 30 3 2500/2500 1. 1 2. 6 30 3 1000/2500 2. 1 4. 9 • The second option is using 1 km medium-energy ion ring for higher proton beam current at 30 Ge. V protons for lowering the space charge tune-shift
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 over 2 1034 cm-2 s-1 KEK B MEIC Repetition rate MHz 509 1497 Particles per bunch 1010 3. 3/1. 4 0. 42/1. 25 Beam current A 1. 2/1. 8 1/3 Bunch length cm 0. 6 1/0. 75 Horizontal & vertical β* cm 56/0. 56 10/2 (4/0. 8) Luminosity per IP, 1033 cm-2 s-1 20 5. 6 (14. 2) JLab believes these ideas should be replicated in the next electron-ion collider ( ): high-luminosity detector
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
Figure-8 Electron Collider Ring
MEIC: Reaching Down To Low Energy electron ring (1 km ) low energy IP A compact (~150 m) ring dedicated to low energy ion 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 Ge. V to 20 Ge. V • Increasing ion current by a factor of 6, thus luminosity by 600%
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 Length Field Dipole 1. 1 m 1. 25 T (2. 14 deg) Quad 0. 4 m 9 k. G/cm Cell 4 m 2 dis. sup. cells 26 FODO cells 2 dis. sup. cells phase adv/cell: 1350 circumference ~1000 m
Electron Polarization in Figure-8 Ring electron spin in vertical direction ions ro elect n spin tuning solenoid electron spin in vertical direction elect ron longi spin in tud direc inal tion Universal Spin Rotators Self polarization time in MEIC Ge. V Hours 3 14. 6 4 3. 5 5 1. 1 6 0. 46 9 0. 06 11 0. 02 • Polarized electron beam is injected at full energy from 12 Ge. V 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
Universal Spin Rotator espin from arc spin 8. 8º 4. 4º E Solenoid 1 Solenoid 2 BL = 28. 712 Tesla m Spin rotation spin rot. BDL arc bend 1 src bend 2 Ge. V rad Tm rad 3 π/2 15. 7 0 0 π/3 π/6 4. 5 π/4 11. 8 π/2 23. 6 π/2 π/4 6 0. 63 12. 3 π-1. 23 38. 2 2π/3 9 π/6 15. 7 2π/3 62. 8 π π/2 12 0. 62 24. 6 π-1. 23 76. 4 4π/3 2π/3 solenoid 4. 16 m decoupling quad insert M= C 0 0 -C solenoid 4. 16 m
Electron Beam Time Structure & RF System From CEBAF SRF Linac 0. 67 ns (20 cm) 1. 5 GHz <3. 3 ps (<1 mm) 0. 2 p. C Microscopic bunch duty factor 5 x 10 -3 MEIC RF operation frequency 10 -turn injection 33. 3 μs (2 p. C) MHz 1. 497 Total Power MW 6. 1 Harmonic number RF Voltage 40 ms (~5 damping times) 25 Hz Beam current Energy loss per turn 4969 MV 4. 8 A 3 Me. V 2 R/Q 3000 “pulses” =120 s HOM Power Accelerating voltage gradient Unloaded Q Number of cavities 90 k. W 2 MV/m 1 1. 2× 109 16
Possible Electron Ring RF Systems CESR PEP II BESSY RF may prefer 748. 5 MHz (coupler limits)
Beam Synchronization • Electron speed is already speed of light at 3 to 11 Ge. V, ion speed is not, there is 0. 3% variation of ion speed from 20 to 60 Ge. V • 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 Ge. V), change ion path length ion arc on movers – At the lower energies (close to 20 Ge. V), 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 e. RHIC e-Ring Path Length Adjustment Harmonic Number vs. Proton Energy (e. RHIC Ring-Ring Design Report) n β=(h-n)/h γ Energy (Ge. V) 0 1 inf Inf 1 0. 9998 47. 44 43. 57 2 0. 9996 33. 54 30. 54 3 0. 9993 27. 39 24. 76 4 0. 9991 23. 72 21. 32 5 0. 9989 21. 22 18. 97 6 0. 9987 19. 37 17. 24
Ion SRF Linac (First Cut) Ion species for reference design Kinetic energy of lead ions Up to Lead 208 Pb Me. V/u 100 Maximum beam current averaged over the pulse Pulse repetition rate m. A 2 Hz 10 Pulse length ms k. W 680 MHz 115 m • Up to 285 Me. V for H- or 100 Me. V/u for 208 Pb+67 0. 25 Maximum beam pulsed power Fundamental frequency • Accelerating a wide variety of polarized light ions and unpolarized heavy ion 150 Total length • Requires stripper for heavy ions (Lead) for efficiency optimization QWR HWR DSR
MEIC Ion Pre-booster n No 2( SS ARC 3 ARC 1 SS 1 Dispersive m 3 m 0. 4 Max Quad Field (arc) T 0. 81 Dipole m 2 deg 11. 47 Bending angle n. D isp er siv e) e) SS 3 Dispersive v si er 0. 35 Quad sp m Drift (SS) di Drift (arc) 4( SS ARC 4 ARC 2 m 300 Straight (long) No Total length m 2 x 57 Straight (short, in arc) m 2 x 23 deg 95. 35 Figure-8 angle Max particle γ 4. 22 Transition γ 5. 4 Momentum compaction 0. 0341
Detector Concept and IR Layout central detector with endcaps large aperture electron quads dipole IP dipole small diameter electron quads ~50 mrad crossing Solenoid yoke + Muon Detector Tracking 5 m solenoid Pawel Nadel-Turonski EM Calorimeter Hadron Calorimeter Muon Detector RICH HTCC EM Calorimeter Solenoid yoke + Hadronic Calorimeter RICH low-Q 2 electron detection small angle hadron detection quads ultra forward hadron detection dipole
DISP_X&Y[m] BETA_X&Y[m] 800 5 IR Optics (electrons) IP Natural Chromaticity: x = -47 0 0 f 0 BETA_X BETA_Y FF doublets DISP_X DISP_Y l * = 3. 5 m 19 y = -66
Synchrotron Radiation Background 50 mrad 38 8. 5 x 105 2. 5 W Photons incident on various surfaces from the last 4 quads 4. 6 x 104 240 2 3080 Rate per bunch incident on the surface > 10 ke. V Beam current = 2. 32 A 2. 9 x 1010 particles/bunch M. Sullivan July 20, 2010 F$JLAB_E_3_5 M_1 A Rate per bunch incident on the detector beam pipe assuming 1% reflection coefficient and solid angle acceptance of 4. 4 % Michael Sullivan, SLAC
Beam-Beam Studies • Simulating the beam-beam effects becomes critically important as part of the feasibility study of this conceptual design • Staged approach to simulations: – Current: isolate beam-beam effects at IP (idealized linear beam transport) – Next: incorporate non-linearity in the beam transport around the ring • Main points of this stage of beam-beam simulations: – Developed a new, automated search for working point based on an evolutionary algorithm (near half-integer resonance: exceeds design luminosity by ~33%) – Short-term stability verified to within capabilities of strong-strong code – As beam current is increased, beam-beam effects do not limit stability – Beam-beam effects are not expected limit the capabilities of the MEIC
Electron Beam Stability The following issues have been studied: • Impedances • Inductive impedance budget • Resistive wall impedance • CEBAF cavity • HOM loss • Single bunch instabilities • Multibunch instabilities • Intrabeam scattering • Touschek scattering • Beam-gas scattering • Ion trapping & fast beam-ion instability • Electron clouds • As long as design of vacuum chamber follows the examples of ring colliders, especially B-factories, we will be safe from the single bunch instabilities. • No bunch lengthening and widening due to the longitudinal microwave instability is expected • No current limitation from transverse mode coupling instability. • The performance of MEIC e-ring is likely to be limited by multi-bunch instabilities. Feedback system able to deal with the growth has to be designed. • All ion species will be trapped. Total beam current limitation and beam lifetime will depend upon the ability of the vacuum system to maintain an acceptable pressure, about 5 n. Torr in the presence of 3 A of circulating beam.
ERL Circulator Cooler Design goal • Up to 33 Me. V electron energy • Up to 3 A CW unpolarized beam (~n. C bunch charge @ 499 MHz) • Up to 100 MW beam power! Solution: ERL Circulator Cooler Electron circulator ring • ERL provides high average current CW beam with minimum RF power • Circulator ring for reducing average current from source and in ERL (# of circulating turns reduces ERL current by same factor) Technologies • High intensity electron source/injector • Energy Recovery Linac (ERL) • Fast kicker
Forming the High-Intensity Ion Beam low energy ring cooling SRF Linac source pre-booster. Accumulator ring Medium energy collider ring Energy (Ge. V/c) Stacking proton beam in ACR Circumference Energy/u Cooling electron current Cooling time for protons Stacked ion current Norm. emit. after stacking Cooling m Ge. V A ms A µm 100 0. 2 -0. 4 1 10 1 16 Process Source/SRF linac 0. 2 Full stripping Prebooster/Accumulator-Ring 3 DC electron Stacking/accumulating Low energy ring (booster) 12 Electron RF bunching (for collision) Medium energy ring 60 Electron RF bunching (for collision) Stacking/accumulation process § Multi-turn (~20) pulse injection from SRF linac into the prebooster § Damping/cooling of injected beam § Accumulation of 1 A coasted beam at space charge limited emittance § Fill prebooster/large booster, then accelerate § Switch to collider ring for booster, RF bunching & staged cooling
MEIC Critical Accelerator R&D We have identified the following critical R&D for MEIC: • • Interaction region design and limits with chromatic compensation Electron cooling Crab crossing and crab cavity Forming high intensity low energy ion beam Beam-beam effect Beam polarization and tracking Traveling focusing for very low energy ion beam Level of R&D Low-to-Medium Energy (12 x 3 Ge. V/c) & (60 x 5 Ge. V/c) High Energy (up to 250 x 10 Ge. V) Challenging Semi Challenging Likely Know-how IR design/chromaticity Electron cooling Traveling focusing (for very low ion energy) IR design/chromaticity Electron cooling Crab crossing/crab cavity High intensity low energy ion beam Spin tracking Beam-Beam Spin tracking Beam-beam
MEIC Enabling Technologies • Pushing the limits of present accelerator theory – Issues associated with short ion bunches (e. g. . cooling) – Issues associated with small β* at collision points • Focus on chromatic compensation – Beam-beam effects • Development of new advanced concepts – Dispersive crabbing – Beam-based fast kicker for circulator electron cooler
Achieving High Luminosity MEIC design luminosity L~ 6 x 1033 cm-2 s-1 for medium energy (60 Ge. V x 3 Ge. V) Luminosity Concepts • • High bunch collision frequency (0. 5 GHz, can be up to 1. 5 GHz) Very small bunch charge (<3 x 1010 particles per bunch) Very small beam spot size at collision points (β*y ~ 5 mm) Short ion bunches (σz ~ 5 mm) Keys to implementing these concepts • Making very short ion bunches with small emittance • SRF ion linac and (staged) electron cooling • Need crab crossing for colliding beams Additional ideas/concepts • Relative long bunch (comparing to beta*) for very low ion energy • Large synchrotron tunes to suppress synchrotron-betatron resonances • Equal (fractional) phase advance between IPs
Straight Section Layout y z Minimizing crossing angle reduces crab cavity challenges straight section spin rotator e arc dipoles vertical bend collision point e collision point i spin rotator ~0. 5 m arc bend i vertical spin vertical bend rotators bend Vertical crossing angle (~30 mrad) Optional 2 nd detector Interaction Region ~ 60 m IP FODO Crab cavity Chrom Matching FF quads Detector space FF Matching Chrom Crab FODO quad cavity
MEIC Science Drivers Key issues in nucleon structure & nuclear physics Sea quark and gluon imaging of nucleon with GPDs (x >~ 0. 01) Orbital angular momentum, transverse spin, and TMDs QCD vacuum in hadron structure and fragmentation Nuclei in QCD: Binding from EMC effect, quark/gluon radii from coherent processes, transparency Machine/detector requirements • High luminosity > 1034: Low rates, differential measurements • CM energy s~1000 Ge. V 2: Reach in Q 2, x • Detectability: Angular coverage, particle ID, energy resolution favors lower & more symmetric energies ECM (Ge. V) 50 fb-1 120 xmin ~ 10 -4 gluon 100 saturation 80 60 40 20 0 quarks, gluons in nuclei DIS nucleon structure exclusive, electroweak processes • • MEIC xmin ~ 10 -3 xmin ~ 10 -2 1 R. Ent 10 MEIC sin 2θ W 100 ∫L dt (fb-1)