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 ( ) 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

Accelerator R&D EICAC Recommendations• 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

EICAC Report, Feb. 2010

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-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 kW/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 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

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 2x1034 /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

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

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

Particles per Bunch A few of 1010 A few of 1011 1/10

Bunch length 0.5 cm 70 to 100 cm 1/100

Beta-star 0.5 to 1 cm 30 to 100 cm 1/100

Beam-beam tune-shift 0.1 0.025 4

Luminosity per IP 2x1034 Up to a few of 1032 50 to 100

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

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,yxy

py

p

eppy

Nr

• 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

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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 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

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 chargeSingle bunch effects such as space charge tune shift could get much worse

• Longer bunch lengthHigh 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.

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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

EnergyWide 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 ion

and 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-1 per 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 Beam desirable

MEIC Design Goals

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)

MEIC : Detailed Layout

cold ring

warm ring

ELIC: High Energy & Staging

Stage Max. Energy (GeV/c)

Ring Size (m)

Ring Type IP #

p e p e

Medium

96 11 1000 ColdWarm

3

High 250 20 2500 ColdWarm

4

Serves as a large booster to the full energy collider ring

Arc

Straight section

MEIC Design Parameters For a Full-Acceptance Detector

Proton Electron

Beam energy GeV 60 5

Collision frequency GHz 0.75 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

Distance from IP to 1st FF quad m 7 3.5

Luminosity per IP, 1033 cm-2s-1 5.6

Proton Electron

Beam energy GeV 60 5

Collision frequency GHz 0.75 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 0.8

Vertical beam-beam tune shift 0.007 0.03

Laslett tune shift 0.014 Very small

Distance from IP to 1st FF quad m 4.5 3.5

Luminosity per IP, 1033 cm-2s-1 14.2 (20)

MEIC Design Parameters For a High-Luminosity Detector

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 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

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 (~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

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

MEIC Ion Complex As We Envisioned

source SRF Linac Pre-booster-

Accumulator ring

Large booster-Low energy collider ring

Medium energy collider ring

cooling

Cooling (for collision beam)

Cooling (for accumulation)

Maximum Energy (GeV/c)

Cooling Processes

Source/SRF linac 0.2 Full stripping

Prebooster/Accumulator-Ring

3 to 5 DC electron Stacking/accumulating

Large boosterLow energy ring

12 to 20Electron

(for collision)RF bunching (for

collision)

Medium energy ring60 to 100 Electron

RF bunching (for collision)

Electron Cooling of Colliding Ion Beams

10 mSolenoid

(7.5 m)

SRF ERL

injector

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 (Derbene

v)

IBS(Piwinski

)

IBS(Derbene

v)

s s s

Horizontal

7.8

86

longitudinal

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 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

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)

Future Accelerator R&DWe 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 ringStart 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?

Future Accelerator R&DFocal Point 3: Forming high-intensity short-bunch ion beams &

coolingSub tasks: Ion bunch dynamics and space charge effects (simulations)

Electron cooling dynamics (simulations) Dynamics of cooling electron bunch in

ERL circulator ringLed 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

Proton Energy

Electron Energy

S CM Energy

Luminosity(L=7m, β*=2cm)

Luminosity(L=4.5m, β*=8mm)

GeV GeV GeV2 GeV 1033 cm-2s-1 1033 cm-2s-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

Assuming maximum peak field of ion magnet 8 Tesla, highest proton energy can be 96 GeV

MEIC Luminosity: 1 km Ring, 8 Tesla

Large acceptance High luminosity

Proton Energy

Electron Energy

s CM Energy

Luminosity(L=7m, β*=2cm)

Luminosity(L=4.5m, β*=8mm)

GeV GeV GeV2 GeV 1033 cm-2s-1 1033 cm-2s-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=7m, β*=2cm)

Luminosity(L=4.5m, β*=8mm)

GeV GeV m 1033 cm-2s-1 1033 cm-2s-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 GeV protons for lowering the space charge tune-shift

ELIC Luminosity: 2.5 km Ring, 8 TeslaLarge acceptance

High luminosity

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 21034 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-2s-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

Compact low energy

ion ring

electron ring(1 km )

Medium energy IP

low energy IP A compact (~150 m) ring dedicated to low energy ion

• 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%

Electron Collider Ring

4.030510

Mon Jun 28 19:07:51 2010 OptiM - MAIN: - C:\Working\ELIC\MEIC\Optics\Electron Ring_1000\cell_in.opt

15

0

0.1

50

BE

TA

_X

&Y

[m]

DIS

P_

X&

Y[m

]

BETA_X BETA_Y DISP_X DISP_Y

Length Field

Dipole 1.1 m 1.25 T (2.14 deg)

Quad 0.4 m 9 kG/cm

Cell 4 m

4.030510

Mon Jun 28 19:11:11 2010 OptiM - MAIN: - C:\Working\ELIC\MEIC\Optics\Electron Ring_1000\cell_in.opt

0.5

0P

HA

SE

_X

&Y

Q_X Q_Y

phase adv/cell: 1350

-10000

-8000

-6000

-4000

-2000

0

2000

4000

6000

8000

10000

-20000 -15000 -10000 -5000 0 5000 10000 15000 20000x [cm]

z [cm]

Figure-8 Collider Ring - Footprint

circumference ~1000 m

1200

Mon Jun 28 19:23:50 2010 OptiM - MAIN: - C:\Working\ELIC\MEIC\Optics\Electron Ring_1000\quart_arc_in_per.opt

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0.1

50

BE

TA

_X

&Y

[m]

DIS

P_

X&

Y[m

]

BETA_X BETA_Y DISP_X DISP_Y

26 FODO cells2 dis.

sup. cells2 dis.

sup. cells

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

135º FODO Cell for arc

One quarter arc

Electron Polarization in Figure-8 Ring

GeV Hours

3 14.6

4 3.5

5 1.1

6 0.46

9 0.06

11 0.02

electron spin in vertical directionions

electron

Universal Spin Rotators

spin tuning solenoid

electron spin in longitudinal direction

Self polarization time in MEIC

electron spin in vertical direction

• 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

Universal Spin Rotator

E Solenoid 1

Solenoid 2 Spin rotation

spin rot.

BDL

spin rot.

BDL arc bend

1

src bend

2

GeV rad T m rad T m rad 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 π/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

e-

spin

spin

8.8º4.4º

from arc

solenoid 4.16 m

solenoid 4.16 m

decoupling quad insert

17.90320

Tue Jul 13 22:27:07 2010 OptiM - MAIN: - C:\Working\ELIC\MEIC\Optics\5GeV Electe. Ring\sol_rot_2.opt

15

0

50

BE

TA

_X

&Y

[m]

BETA_1X BETA_2Y BETA_1Y BETA_2X

BL = 28.712 Tesla m

M =C

C

0

0

Electron Beam Time Structure & RF System

<3.3 ps(<1 mm)0.2 pC

0.67 ns (20 cm)1.5 GHz

10-turn injection 33.3 μs (2 pC)

40 ms (~5 damping times)

25 Hz

3000 “pulses” =120 s

Microscopic bunch duty factor 5x10-3

From CEBAF SRF

Linac

MEIC

RF operation frequency MHz 1.497

Total Power MW 6.1

Harmonic number 4969

RF Voltage MV 4.8

Beam current A 3

Energy loss per turn MeV 2

R/Q 90

HOM Power kW 2

Accelerating voltage gradient

MV/m 1

Unloaded Q 1.2×109

Number of cavities 16

PEP II

CESR

BESSY

Possible Electron Ring RF Systems

RF may prefer 748.5 MHz (coupler limits)

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

eRHIC e-Ring Path Length Adjustment

(eRHIC Ring-Ring Design Report)n β=(h-n)/h γ Energy

(GeV)

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

Harmonic Number vs. Proton Energy

Ion SRF Linac (First Cut)

Ion species Up to Lead

Ion species for reference design

208Pb

Kinetic energy of lead ions

MeV/u 100

Maximum beam current averaged over the pulse

mA 2

Pulse repetition rate Hz 10Pulse length ms 0.25Maximum beam pulsed power

kW 680

Fundamental frequency MHz 115Total length m 150

IS MEBT Stripper

RFQ IH QWR QWR HWR DSR (3 m) (9 m) (24 m) (12 m) (24 m) (50 m)

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

MEIC Ion Pre-booster

Drift (arc) m 0.35

Drift (SS) m 3

Quad m 0.4

Max Quad Field (arc) T 0.81

Dipole m 2

Bending angle deg 11.47

ARC1

SS

1 D

isp

ers

ive

ARC2

SS2(Non dispersive)

ARC3

SS

3 D

isp

ers

ive

ARC4 SS4

(Non

Dis

pers

ive)

Total length m 300

Straight (long) m 2x57

Straight (short, in arc) m 2x23

Figure-8 angle deg 95.35

Max particle γ 4.22

Transition γ 5.4

Momentum compaction 0.0341

Detector Concept and IR Layout

IP

EM

Cal

orim

eter

Had

ron

Cal

orim

eter

Muo

n D

etec

tor

EM

Cal

orim

eter

Solenoid yoke + Hadronic Calorimeter

Solenoid yoke + Muon Detector

HT

CC

RIC

H

RICH

Tracking

ultra forwardhadron detection

dipole

dipole

low-Q2

electron detectionlarge apertureelectron quads

small diameterelectron quads

ion quads

small anglehadron detection

dipole

central detector with endcaps

5 m solenoid

~50 mrad crossing

Pawel Nadel-Turonski

IR Optics (electrons)

2 1

* *IR

f f

f

Natural Chromaticity:

x = -47 y = -66

190

800

0

50

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]

BETA_X BETA_Y DISP_X DISP_Y

*

*

10

2

x

y

cm

cm

l * = 3.5m

IP

FF doublets

f

*2 2

* 223.5

6 102 10

ff m

2*

*( )

max0FFg

Synchrotron Radiation Background

M. SullivanJuly 20, 2010F$JLAB_E_3_5M_1A

FF1 FF2

e-

P+

1 2 3 4 5-1

40 mm30 mm

50 mm

240

3080

4.6x104

8.5x105

2.5W

38

2

Rate per bunch incident on the surface > 10 keV

Rate per bunch incident on the detector beam pipe assuming 1% reflection coefficient and solid angle acceptance of 4.4 %

50 mrad

Beam current = 2.32 A 2.9x1010 particles/bunch

Photons incident on various surfaces from the last 4 quads

Michael Sullivan, SLAC

• 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

Beam-Beam Studies

Electron Beam Stability

• 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 nTorr in the presence of 3 A of circulating beam.

The following issues have been studied:

ERL Circulator CoolerDesign goal• Up to 33 MeV electron energy• Up to 3 A CW unpolarized beam

(~nC bunch charge @ 499 MHz)• Up to 100 MW beam power!

Solution: ERL Circulator Cooler

• 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

Electron circulator

ring

Forming the High-Intensity Ion Beam

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

Circumference m 100Energy/u GeV 0.2 -0.4Cooling electron

current A 1

Cooling time for protons

ms 10

Stacked ion current A 1Norm. emit. after

stackingµm 16

Stacking proton beam in ACR

Energy (GeV/c)

Cooling Process

Source/SRF linac 0.2 Full stripping

Prebooster/Accumulator-Ring

3DC

electronStacking/accumulating

Low energy ring (booster)12 Electron

RF bunching (for collision)

Medium energy ring60 Electron

RF bunching (for collision)

source

SRF Linac

pre-booster-Accumulator ring

low energy ring

Medium energy collider ring

cooling

MEIC Critical Accelerator R&D

Level of R&D

Low-to-Medium Energy(12x3 GeV/c) & (60x5 GeV/c)

High Energy(up to 250x10 GeV)

Challenging

Semi Challenging

IR design/chromaticityElectron coolingTraveling focusing (for very low ion energy)

IR design/chromaticityElectron cooling

Likely Crab crossing/crab cavityHigh intensity low energy ion beam

Crab crossing/crab cavityHigh intensity low energy ion beam

Know-how Spin trackingBeam-Beam

Spin trackingBeam-beam

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

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~ 6x1033 cm-2 s-1 for medium energy (60 GeV x 3 GeV)

Luminosity Concepts• High bunch collision frequency (0.5 GHz, can be up to 1.5

GHz)• Very small bunch charge (<3x1010 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

spin rotators

spin rotator

collision point

collision point

vertical bend

ii

ee

arc dipoles ~0.5 m arc bend

spin rotator

vertical bend

vertical bend

~0.5 m

vertical bend

y

z straight section

Vertical crossing angle (~30 mrad)

Minimizing crossing angle reduces crab cavity challenges

Detector space

IP

~ 60 m

FFFF Crab cavity

Matching quad

Chrom FODOMatching quads

ChromCrab cavity

FODO

Interaction Region

Optional 2nd detector

MEIC Science DriversKey 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 GeV2: Reach in Q2, x

• Detectability: Angular coverage, particle ID, energy resolution

∫L dt (fb-1)

0

20

40

60

80

100

120

1 10 100

gluon saturation

sin2θ

Wxmin ~ 10-2

xmin ~ 10-3

xmin ~ 10-4

50 fb-1

MEIC

favors lower & more symmetric energies

R. Ent

MEIC