4 th EIC Workshop Hampton University, VA Richard Milner 1 Electron-Ion Collider Accelerator Workshop...

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4th EIC Workshop

Hampton University, VARichard Milner

Electron-Ion ColliderAccelerator Workshop Summary

and OutlookEIC biennial meeting

Hampton, VAMay 2008

R. MilnerMIT

Presentation based on work and contributions from L. Merminga, V. Litvinenko, V. Ptitsyn, C. Tschalär,

E. Tsentalovich, Y. Zhang and their colleagues

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4th EIC Workshop


• Concepts

• 20 – 100 GeV c.m. Energy eRHIC (BNL) Ring-ring Electron linac – ion ring ELIC (JLab) Ring-ring

• Polarized electron gun development • Conclusions and outlook

Outline

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4th EIC Workshop


Lepton Beam FacilitiesQuarks discovered

Gluon momentum distribution measured

Nucleon spin structure studied

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• High luminosity 1033 – 1035 e-nucleon collisions/(cm2s)

• Polarized electron and positron beams• Polarized nucleon (proton, deuteron, 3He)

beams• Heavy ion beams (He to Uranium) • Integrated luminosity:

50 fb-1 over about a decade

Concepts:• Ring-ring: e- / e+ storage ring intersects ion

storage ring

• Linac-ring: e- from ERL intersect ion storage ring

Physics considerations

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Challenges and Limitations1. Luminosity

Ring-ring colliders Beam-beam tune shift ξ limited

y k= / x 2( ) ( ) (1+k) /

= r.m.s beam divergence at IP

c x yx y eieiL f kr r

Empirical limits: ξe ≤ 0.1 ; ξi ≤ 0.015

Linac- ring Colliders

No electron tune shift limit (“once through” beam)

Polarized electron current Ie limited (polarized source)

2 (1 )e iNLk

I

Ion emittance єi limited →cooling

IP beam spot limited: єe,βe,βi

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2. PolarizationProton and 3He beams from polarized sources

Siberian snakes prevent depolarization during acceleration

Ring-ring:

• Polarized electrons from laser driven GaAs source, low current

(≤ 1mA ; 70-80% pol.)

• Non-depolarizing accelerator (linac, fig.-8 syncrotron)

• Stack and store in “spin transparent” ring

• Positrons from positron source (unpolarized)

accelerate, stack into storage ring, self-polarize (Sokolov-Ternov)

Linac-ring:

• Polarized electrons from ultra-high current GaAs source

(≥ 100mA ; 70-80% pol.)

• Accelerate in ERL, intersect ion ring, recover beam energy (>1 GW)

Challenges and Limitations (contd.)

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eRHIC ring-ring layout50-250 GeV polarized protons; 50-100 GeV/n ions, He-U

Polarized 3He source

5-10 GeV electrons/positrons

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4th EIC Workshop


eRHIC (BNL)

Ring-Ring EIC

• Electron/positron storage ring 5-10 GeV• 1.2 km circumference (1/3 RHIC) optimized for: cost, synchrotron light power, e+ polarization time

• “Superbends” for optimal emittance, pol. time at all energies• Full-energy injection: recirculating linacs, or fig.-8 fast

synchrotron; Positron source• Polarized injection; optimized ring; top-off mode• “Spin transparent” lattice, no vertical bends, spin resonances, ~ 5 min. self-polarization time• Ring circumference adjustable to ion energy (RHIC orbital

frequency) - “Trombone”

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eRHIC ring-ring parameters

High energy setup Low energy setup

p e p e

Energy, GeV GeV 250 10 50 5

Number of bunches 165 55 165 55

Bunch spacing ns 71 71 71 71

Particles / bunch 1011 1.00 2.34 1.49 0.77

Beam current mA 208 483 315 353

95% normalized emittance mm·mrad 15 5

Emittance x nm 9.5 53.0 15.6 130

Emittance y nm 9.5 9.5 15.6 32.5

x* m 1.08 0.19 1.86 0.22

y* m 0.27 0.27 0.46 0.22

Beam-beam parameter x 0.015 0.029 0.015 0.035

Beam-beam parameter y 0.0075 0.08 0.0075 0.07

Bunch length z m 0.20 0.012 0.20 0.016

Polarization % 70 80 70 80

Peak Luminosity 1033 cm-2s-1 0.47 0.082

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Status

• Lattice design concept → finalize spin tracking, beam-beam effects

• Injection concept → cost optimization

• Interaction point concept → optimize with detector designs

• No major R&D

• Solid cost estimate

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4th EIC Workshop


PHENIX

STAR

e-ion detector

eRHIC

eRHIC ERL-based Design

Four recirculation passes

Main ERL (1.9 GeV)

Low energy recirculation pass

Beam dump

Electronsource

Possible locationsfor additional e-ion detectors

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Advantages & Challenges of ERL based eRHIC

• This scheme takes full advantage of cooling of the hadron beams

• Uses RHIC tunnel for the return passes.• High luminosity up to 1034 cm-2 sec-1

• Allows multiple IPs• Allows higher range of CM-energies with high luminosities• Full spin transparency at all energies• No machine elements inside detector(s)• No significant limitation on the lengths of detectors• Energy of ERL is simply upgradeable• Polarized electron gun requirements x100 to 1000 above

existing• Needs completion of e-cooling R&D (CeC and conventional)

frr

L eieiei

ei ''4

ii

iiii r

ZNfL

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ERL-based eRHIC ParametersHigh energy setup Low energy setup

p e p e

Energy, GeV 250 10 50 3

Number of bunches 166 166

Bunch spacing, ns 71 71 71 71

Bunch intensity, 1011 2 1.2 2.0 1.2

Beam current, mA 420 260 420 260

Normalized 95% emittance, p mm.mrad

6 460 6 570

Rms emittance, nm 3.8 4 19 16.5

*, x/y, cm 26 25 26 30

Beam-beam parameters, x/y 0.015 0.59 0.015 0.47

Rms bunch length, cm 20 1 20 1

Polarization, % 70 80 70 80

Peak Luminosity, 1.e33 cm-2s-1

Aver.Luminosity, 1.e33 cm-2s-1

2.6 0.53

0.87 0.18

Luminosity integral /week, pb-1 530 105

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Main R&D Items• Electron beam R&D for ERL-based design:

– High intensity polarized electron source

• Development of large cathode guns with existing current densities ~ 50 mA/cm2 with good cathode lifetime.

– Energy recovery technology for high power beams

• Multicavity cryomodule development; BNL test ERL; loss protection; instabilities.

– Development of compact recirculation loop magnets

• Design, build and test a prototype of a small gap magnet and its vacuum chamber.

– Evaluation of electron-ion beam-beam effects, including the kink instability and e-beam disruption

• Main R&D items for ion beam:

– Polarized 3He production (EBIS) and acceleration

– 166 bunches

• General EIC R&D item:

– Proof of principle of the coherent electron cooling

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4th EIC Workshop


ERL Test Facility

50 kW 703.75 MHzsystem

Cryo-module

SRF cavity

1 MW 703.75 MHzKlystron

e- 2.5MeV

Laser

SC RF Gun e- 2.5 MeV

Beam dump

Cryo-module

e- 15-20 MeV

Merger system

Return loop

• test of high current (~ 0.5 A) high brightness ERL operation• 5-cell cavity SRF ERL • test of high current beam stability issues• highly flexible lattice• 704 MHz SRF gun test

Start of commissioning in 2009.

D.Kayran’s talk at the Parallel session 5 cell SRF cavity arrived in BNL in March 2008 .

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eRHIC

Recirculation passes Separate recirculation loops Small aperture magnets Low current, low power

consumption Minimized cost

5 mm

5 mm

5 mm

5 mm

10 GeV (20 GeV)

8.1 GeV (16.1 GeV)

6.2 GeV (12.2 GeV)

4.3 GeV (8.3 GeV)

Com

mon v

acu

um

ch

am

ber

Approved LDRD for the compact magnet development

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4th EIC Workshop


Interaction Region Design

Present IR design features: No crossing angle at the IP Detector integrated dipole: dipole field

superimposed on detector solenoid. No parasitic collisions. Round beam collision geometry with

matched sizes of electron and ion beams. Synchrotron radiation emitted by electrons

does not hit surfaces in the detector region. Blue ion ring and electron ring magnets are

warm. First quadrupoles (electron beam) are at 3m

from the IP Yellow ion ring makes 3m vertical

excursion.

(Blue) ion ring magnets

(Red) electron beam magnets

(Yellow) ion ring magnets

Detector

HERA type half quadrupoleused for proton beam focusing

C.Montag’s talk at the Parallel session

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Novel features • Coherent electron cooling - the key for many novel features in eRHIC • Choosing the focus: ERL for electrons

– Advantages and challenges of ERL driver• spin transparency

– R&D items for ERL-based eRHIC• eRHIC is the future of RHIC: eRHIC staging

– Energy challenge – 20 GeV e x 325 GeV p and 30 GeV e x 125 GeV/n heavy ions – Loss on synchrotron radiation– Polarized beam current

• Luminosity challenge:– Can eRHIC deliver 1035 cm-2 sec-1 luminosity?– High rep-rate, crab cavities, coating RHIC arc vacuum chambers and more

• Other novelties and oldies– Low (350 MHz) RF frequency, no 3rd harmonic, higher real estate gradient – Small magnets for re-circulating passes, resistive-wall losses– e-lens or fast a quads for matching ERL beam– compact and flexible separators and combiners– Possibility of eRHIC II up-grade

V. Litvinenko

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Stage I -RHIC with ERL inside RHIC tunnel

Medium energy EIC with 2 GeV ERL @ IP2

Asymmetric detector 0.95 GeV SRF linac

100 MeV ERL2 GeV e-beam pass through the detector 3 vertically separated

passes at 0.1 GeV, 1.05 and 2 GeV

Don’t forget the polarizedelectrons!

V. Litvinenko

• Lively discussion on Tuesday afternoon• Many issues raised• Consideration will continue

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Proof of Principle test for Coherent Electron Cooling

IR-2 in RHIC

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eRHIC polarized electron gun (linac-ring)

Extremely high current demand !!!

I(average) ~ 500 mA

I(peak) ~ 200 A

High polarization → strained GaAs → QE ~ 0.1%

124/(%)QE)W(P)nm()mA(I laser

Average laser power ~ 800 W

Such lasers do not exist. Possible solutions:

a) array of diode lasers

b) dedicated FEL – almost unlimited laser power, tunable

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Damage location

Electrons follow electrical field lines, but ions have different trajectory. Usually, they tend to damage central area of the cathode.

Laser spot

Cathode Damage groove

JLAB data

Ring-like cathodes ?

E. Tsentalovich, MIT-Bates

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4th EIC Workshop


Axicon Beam Profile

-3

-2.4

-1.8

-1.2

-0.6

0

0.6

1.2

1.8

2.4

3

-3

-2.4

-1.8

-1.2

-0.6

0

0.6

1.2

1.8

2.4

3

0

1

2

3

4

5

6

7

8

9

109-10

8-9

7-8

6-7

5-6

4-5

3-4

2-3

1-2

0-1

2mm9S

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QE change (small spot in the corner)

Run 16.84 C

-5-4

-3-2

-10

12

34

5

-5

-3

-1

1

3

5

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

a17-a16

0.9-1

0.8-0.9

0.7-0.8

0.6-0.7

0.5-0.6

0.4-0.5

0.3-0.4

0.2-0.3

0.1-0.2

0-0.1

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Lifetime

0

0.5

1

1.5

0 10 20 30 40 50

Time, hours

QE

, %

Axicon, anode grounded, t~120h Axicon, anode at 1 kV, t~230hLarge spot X1.4, t~60h small spot (center) X17, t~50h

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Cathode Cooling

Water in

Water out

HV

Laser

Manipulator

Cathode

Crystal

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ELIC Conceptual Design

3-9 GeV electrons

3-9 GeV positrons

30-225 GeV protons

15-100 GeV/n ions

Green-field design of ion complex directly aimed at full exploitation of science program.

prebooster

12 GeV CEBAF

Upgrade

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High Luminosity with ELIC

ELIC design luminosity

L~ 7.7 x 1034 cm-2 sec-2 (150 GeV protons x 7 GeV electrons)

ELIC luminosity design considerations• High bunch collision frequency (f=1.5 GHz)

• Short ion bunches (σz ~ 5 mm)

• Super strong final focusing (β* ~ 5 mm)

• Large beam-beam parameters (0.01/0.086 per IP,

0.025/0.1 largest achieved)

• Need high energy electron cooling of ion beams

• Need crab crossing

• Large synchrotron tunes to suppress synch-betatron resonances

• Equidistant phase advance between four IPs

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ELIC Design Parameters

Parameter Unit Ring-Ring

Beam energy GeV 225/9 150/7 100/5 30/3

e/A ring circumference km 1.5

Bunch collision frequency GHz 1.5

Number of particles/bunch 1010 0.42/.77 0.4/1 0.4/1.1 0.12/1.7

Beam current A 1/1.85 1/2.4 1/2.7 0.3/4.1

Energy spread, rms 10-4 3/3

Bunch length, rms mm 5/5

Beta* mm 5/5

Horizontal emittance, norm m 1.25/90 1/90 .7/70 .2/43

Vertical emittance, norm m .05/3.6 .04/3.6 .06/6 .2/43

Beam-beam tune shift (vertical) per IP

.006/.086 .01/.086 .01/.078 .009/.008

Peak luminosity per IP, 1034

(including hourglass effect) cm-2 s-1 5.7 6.0 5.0 .7

Number of IPs 4

Core & lumi. IBS lifetime hrs 24

Ion Max Energy

(Ei,max)

Luminosity/n

(7GeVxEi,m

ax)

Luminosity/n

(3GeVxEi,ma

x/5)

(GeV/n) 1034 cm-2 s-

1

1033 cm-2 s-1

Proton 150 7.8 6.7

Deuteron

75 7.8 6.7

3H+1 50 7.8 6.7

3He+2 100 3.9 3.3

4He+2 75 3.9 3.3

12C+6 75 1.3 1.1

40Ca+20 75 0.4 0.4

208Pb+82 59 0.1 0.1

e/p e/A

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ELIC ring-ring design features Unprecedented high luminosity

Enabled by short ion bunches, low β*, high rep. rate

Large synchrotron tune

Require crab crossing

Electron cooling is an essential part of ELIC

Four IPs (detectors) for high science productivity

“Figure-8” ion and lepton storage rings

Ensure spin preservation and ease of spin manipulation

No spin sensitivity to energy for all species.

Present CEBAF gun/injector meets storage-ring requirements

The 12 GeV CEBAF can serve as a full energy injector to electron ring

Simultaneous operation of collider and CEBAF fixed target program.

Experiments with polarized positron beam are possible.

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Figure-8 ring

-20000

-10000

0

10000

20000

-40000 -30000 -20000 -10000 0 10000 20000 30000 40000

z [cm]

x [cm]362 m 152

m

80 deg

Figure-8 Ring - FootprintSmall Ring

Large Ring

Circumference m 2100 2500

Radius m 152 180

Width m 304 360

Length m 776 920

Straight m 362 430

Ion ring

electron ringVertical crossing

Interaction Point

Design is determined by

• Synchrotron radiation power

• Arc bending magnet strength

• Length of crossing straights

• Cost and fit to site Stacked vertically

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Electron polarization in ELICProducing at source Polarized electron source of

CEBAF Preserved in acceleration at

recirculated CEBAF Linac Injected into Figure-8 ring with

vertical polarization

Maintaining in the ring High polarization in the ring by

electron self-polarization SC solenoids at IPs removes spin

resonances and energy sensitivity.

spin rotator

spin rotator

spin rotator

spin rotator

collision point

spin rotator with 90º solenoid snake

collision point

collision point

collision point

spin rotator with 90º solenoid snake

snake solenoid

spin rotator spin rotator

collision point

collision point

spin tune solenoid

spin tune solenoid

spin tune solenoid

spin tune solenoid

ii

ee

spin

90º 90º

Parameter Unit Energy GeV 3 5 7 Beam cross bend at IP mrad 70 Radiation damping time ms 50 12 4 Accumulation time s 15 3.6 1 Self-polarization time* h 20 10 2 Equilibrium polarization, max** % 92 91.5 90 Beam run time h Lifetime

Electron/positron polarization parameters

* Time can be shortened using high field wigglers.** Ideal max equilibrium polarization is 92.4%. Degradation is due to radiation in spin rotators.

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ELIC R&D Requirements

• To achieve luminosity at 1033 cm-2 sec-1 and up High energy electron cooling

• To achieve luminosity at ~ 1035 cm-2 sec-1

Crab cavity

Stability of intense ion beams

Beam-beam interactions

Detector R&D for high repetition rate (1.5 GHz)

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ELIC R&D: Electron Cooling Issue

• To suppress IBS, reduce emittances, provide short ion bunches.• Effective for heavy ions (higher cooling rate), difficult for protons.

State-of-Art• Fermilab e-cooling demonstration (4.34 MeV, 0.5 A DC)• Feasibility of EC with bunched beams remains

to be demonstrated.

ELIC Circulator Cooler• 3 A CW electron beam, up to 125 MeV• Non-polarized source (present/under

developing) can deliver nC bunch• SRF ERL able to provide high average current

CW beam • Circulator cooler for reducing average current

from source/ERL• Electron bunches circulate 100 times

in a ring while cooling ion beam

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ELIC R&D: Crab Crossing High repetition rate requires crab crossing to avoid parasitic beam-beam interaction Crab cavities needed to restore head-on collision & avoid luminosity reduction Minimizing crossing angle reduces crab cavity challenges & required R&D

State-of-art: KEKB Squashed cell@TM110 Mode Crossing angle = 2 x 11 mrad Vkick=1.4 MV, Esp= 21 MV/m

ELIC crab cavity Requirement Electron: 1.2 MV – within state of art

(KEK, single Cell, 1.8 MV)Ion: 24 MV (Integrated B field on axis 180G/4m)

Crab Crossing R&D program • Understand gradient limit and packing factor • Multi-cell SRF crab cavity design capable for high current operation.• Phase and amplitude stability requirements • Beam dynamics study with crab crossing

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Comparison of 20-100 GeV ECM Colliders

Projected performance

eRHIC ELIC

Ring-ring Linac-ring

Electron energy GeV 5-10 3-10 3-9

Pol. Positron energy GeV 5-10 ----- 3-9

Unpol. Positron energy GeV 5-10 3-10 3-9

Proton energy GeV 50-250 50-250

30-225

Ion energy GeV/n 30-100 30-100 20-90

Luminosity 1033/cm2s 0.5 2.5 60

Collision rate MHz 14(28) 14(28) 1500

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Required R&D eRHIC ELIC

Ring-ring Linac-ring Ring-ring

p/ion-beam Raise bunch rep rate to 14 (28) MHz

polarization > 70%

Injector, Fig.8 lattice

beam current 0.5A

Electron cooling

Stochastic cooling

for є ≤ 4 nm

Coher. el. Cooling?

OSC for 250 GeV?

Crab crossing cavities

Electron cooling to

225 GeV

Coherent el. cooling?

OSC ?

e-beam Spin tracking Pol. source 260mA

ERL 2.6 GW beam

15 km recirculator

Spin tracking

Vertical bens

Interaction

Region

Integrating IP and detector design

“close-packed”

Low – β IP region

1500 MHz concept ? pulse rate

C. Tschalär (MIT-Bates)

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Conclusions

• Promising and exciting developments world-wide of high-luminosity polarized electron-ion colliders.

• U.S. nuclear physics accelerator physics capabilities very well matched to needs.

• 2007 NSAC Long-Range Plan recommends accelerator R&D funding for eRHIC and ELIC.

• Intensive EIC R&D effort required to realize aim of single EIC machine design by ~ 2012.

• Continued cooperation and careful coordination essential to get there.

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4th EIC Workshop


Perspective

• To get to next base in realizing EIC, we need to be in position to request a green light at the next long range plan ~ 2013.

• This requires a strong science case, a single machine design and firm cost.

• This will be needed in ~ 2012, four years from now!• We have a unified scientific collaboration working on

the science case.• Could we have a unified EIC accelerator design

group to come to a single machine design?

4 th EIC Workshop Hampton University, VA Richard Milner 1 Electron-Ion Collider Accelerator Workshop...

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