eRHIC Design

Thomas RoserEIC collaboration workshop

MIT, April 6, 2007

eRHIC Design

eRHIC Schemes

R&D Items

Cost and Schedule

eRHIC Scope

Polarized leptons3-20 Gev

Polarized light ions (3He)167 Gev/u

Heavy ions (Au)50-100 Gev/u

Polarized protons50-250 Gev

Electron accelerator RHIC

e-

e+

p

70% beam polarization goal

eRHIC

Integrated electron-nucleon luminosity of ~ 50 fb-1 over about a decade for both highly polarized nucleon and nuclear (A = 2-208) RHIC beams.

50-250 GeV polarized protons up to 100 GeV/n gold ions up to 167 GeV/n polarized 3He ions

Two accelerator design options developed in parallel (2004 Zeroth-Order Design Report):

ERL-based design (“Linac-Ring”; presently most promising design): Superconducting energy recovery linac (ERL) for the polarized electron beam. Peak luminosity of 2.6 1033 cm-2s-1 with potential for even higher luminosities. R&D for a high-current polarized electron source needed to achieve the design goals.

Ring-Ring option: Electron storage ring for polarized electron or positron beam. Technologically more mature with peak luminosity of 0.47 1033 cm-2s-1.

Decision on what to build to supply polarized leptons will be driven by a number of considerations, among them experimental requirements, cost and timeline.

ERL-based eRHIC Design

Electron energy range from 3 to 20 GeV Peak luminosity of 2.6 1033 cm-2s-1 in electron-hadron collisions; high electron beam polarization (~80%); full polarization transparency at all energies for the electron beam; multiple electron-hadron interaction points (IPs) and detectors; 5 meter “element-free” straight section(s) for detector(s); ability to take full advantage of electron cooling of the hadron beams; easy variation of the electron bunch frequency

to match the ion bunch frequency at different ion energies.

0

0.5

1

1.5

2

2.5

3

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Center-Of-Mass Energy, GeV

Pe

ak

Lu

min

os

ity

, 1

033 c

m-2

s-1

3GeV(e)-50GeV(p) 20GeV(e)-50GeV(p)


0

0.5

1

1.5

2

2.5

3

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Center-Of-Mass Energy, GeV

Pe

ak

Lu

min

os

ity

, 1

033 c

m-2

s-1



PHENIX

STAR

e-cooling (RHIC II)

Four e-beam passes

e+ storage ring 5 GeV - 1/4 RHIC circumference

Main ERL (3.9 GeV per pass)

5 mm

5 mm

5 mm

5 mm

Compact recirculation loop magnets

ERL-based eRHIC Parameters

Electron-Proton Collisions Electron-Au Collisions

High energy setup

Low energy setup

High energy setup

Low energy setup

p e p e Au e Au e

Energy, GeV 250 20 50 3 100 20 50 3

Number of bunches 166 166 166 166

Bunch spacing, ns 71 71 71 71 71 71 71 71

Bunch intensity, 1011 (109 for Au) 2.0 1.2 2.0 1.2 1.1 1.2 1.1 1.2

Beam current, mA 420 260 420 260 180 260 180 260

95% normalized emittance, πμm 6 115 6 115 2.4 115 2.4 115

Rms emittance, nm 3.8 0.5 19 3.3 3.7 0.5 7.5 3.3

*, x/y, cm 26 200 26 150 26 200 26 60

Beam-beam parameters, x/y 0.015 2.3 0.015 2.3 0.015 1.0 0.015 1.0

Rms bunch length, cm 20 1.0 20 1.0 20 1.0 20 1.0

Polarization, % 70 80 70 80 0 0 0 0

Peak Luminosity/n, 1.e33 cm-2s-1 2.6 0.53 2.9 1.5

Aver.Luminosity/n, 1.e33 cm-2s-1 0.87 0.18 1.0 0.5

Luminosity integral /week, pb-1 530 105 580 290

Ring-Ring eRHIC Design

Based on existing technology

Collisions at 12 o’clock interaction region

10 GeV, 0.5 A e-ring with 1/3 of RHIC circumference (similar to PEP II HER)

Inject at full energy 5 – 10 GeV

Polarized electrons and positrons

RHIC

5 – 10 GeV e-ring

e-cooling(RHIC II)

5 -10GeV full energy injector

0 50 10010 150 200 250 275 m

2 GeV4 GeV

6 GeV4 GeV

200 MeV

200 MeV

Polarized ElectronSource

Positron Source

2 GeV

Copper Linac, SLAC type cavities10 GeV

8 GeV

1.7 GeV3.3 GeV

5 GeV6.7 GeV

200 MeV

200 MeV

Polarized ElectronSource

Positron Source 3.3 GeV

SC Linac, Tesla type cavities

8.3 GeV10 GeV

0 50 10010 150 200 250 275 m

Recirculating NC linac Recirculating SC linac

Figure 8 booster synchrotron,

FFAG or simple booster

Injection0.5 GeV

Polarized ElectronSource, 20 MeV

Positron Source

0 50 10010 150 m

Extraction5 - 10 GeV

• Injection of polarized electrons from

source

• Ring optimized for maximum current

• Top-off

eRHIC R-R: Full Energy Injection Options

Ring-Ring eRHIC 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

Average Luminosity 1033 , cm-2s-1 0.16 0.027

Luminosity Integral /week pb-1 96 17

eRHIC Ion Beam

RHIC is the world’s only collider of high-energy heavy ion (for now) and polarized proton beams.

100 GeV proton beams with ~ 65% polarization operational First test at 250 GeV reached ~ 45% polarization First high energy stochastic cooling demonstrated in RHIC Electron cooling under development for RHIC II (x10 luminosity). Also

needed/beneficial for eRHIC with same requirements as RHIC II Presently RHIC operates with 111 bunches of 1.4 x 1011 protons. Successful test

of 111 bunches of 3 x 1011 protons at injection. eRHIC design is 166 bunches of 2 x 1011 protons.

Development under way for polarized 3He beams from the new RHIC ion source EBIS

Interaction Region Design

Yellow ion ring makes 3m vertical excursion.

Design incorporates both normal and superconducting magnets.

Fast beam separation. Besides the interaction point no electron-ion collisions allowed.

Synchrotron radiation emitted by electrons does not hit surfaces of cold magnets

(Blue) ion ring magnets

(Red) electron beam magnets

(Yellow) ion ring magnets

Detector

IR Design Schemes

Distance to nearest magnet from IP

Beam separation Magnets usedHor/Ver beam

size ratio

Ring-ring,

l*=1m1m

Combined field quadrupoles

Warm and cold 0.5

Ring-ring, l*=3m

3mDetector

integrated dipoleWarm and cold 0.5

Linac-ring 5mDetector

integrated dipoleWarm 1

No crossing angle at the IP Linac-ring: larger electron beta*; relaxed aperture limits ; allows round beam collision

geometry (the luminosity gains by a factor of 2.5). Detector integrated dipole: dipole field superimposed on detector solenoid.

Main R&D Items (other than engineering and costing)

Electron beam R&D for ERL-based design: High intensity polarized electron source (for polarized beams!)

Development of large cathode guns with existing current densities ~ 50 mA/cm2 with good cathode lifetime. (MIT research proposal)

Energy recovery technology for high energy and high current beams Thorough beam tests with the BNL test ERL based on the 5-cell cavity studying loss

tolerances and the cavity protection systems. 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 Realistic beam-beam simulations.

Electron beam R&D for the ring-ring design: No major R&D items

Main R&D items for ion beam for both designs: Polarized 3He production (EBIS) and acceleration

Develop EBIS as spin-preserving ionizer of optically pumped pol. 3He gas Evaluation of depolarization due to high anomalous magnetic moment of pol. 3He

beams during acceleration in AGS and RHIC

Other R&D

R&D for specific experimental programs:

High precision ion beam polarimeter• Improve absolute polarization accuracy from about 5% to 1%

R&D to further increase eRHIC luminosity:

Increase number of ion bunches from 166 to 333• Electron clouds with 30 ns ion bunch spacing (LHC has 25 ns bunch spacing)• Injection kicker development• Higher current of ERL

Optical stochastic cooling of high energy proton beam• Proof of principal experiment proposed at Bates

Beam-beam compensation• The focusing effect of the colliding electron beam on the ion beam could be

compensated with ion-ion collisions

Ring-ring preliminary cost estimate (2007$)

Electron ring : 132 MInteraction region 9 MInjector (warm recirculating linac, incl. source): 113 MInstallation: 16 MCivil construction: 21 M-----------------------------------------------------------------------------------------Total: 291 M-----------------------------------------------------------------------------------------With PED/EDIA (20%), Contingency (30%) and G&A (15%):Total Equipment Cost (TEC): 523 M

Detector allowance: 103 MPre-ops, R&D: 72 M-----------------------------------------------------------------------------------------Total Project Cost (TPC): ~ 700 M-----------------------------------------------------------------------------------------

Linac-ring preliminary cost estimate (2007$)

4 GeV superconducting linac incl. source: 111 M5 pass recirculation loops (5 x ~15M): 77 MInteraction region: 9 MInstallation: 26 MCivil construction: 21 MCryogenics: 41 MSwitch yards: 21 MPositron capability: 15 M-----------------------------------------------------------------------------------------------Total: 321 M-----------------------------------------------------------------------------------------------With PED/EDIA (20%), Contingency (30%) and G&A (15%):Total Equipment Cost (TEC): 577 M

Detector allowance: 103 MPre-ops, R&D: 72 M-----------------------------------------------------------------------------------------------Total Project Cost (TPC): ~ 750 M------------------------------------------------------------------------------------------------

Straw-man technically driven schedule in 2007$

FY10 FY11 FY12 FY13 FY14 FY15 FY16 FY17 Total

R&D 5 7 5 17

CDR 3 3

PED/EDIA 31 62 23 115

Construction 62 103 144 144 111 564

Pre-ops 16 35 51

TPC 8 38 67 84 103 144 161 146 752

Incremental operations costs: ~ 50 M (2007$)

Summary

Two versions for eRHIC have been developed:

Ring-ring: lower risk (ready to go), lower luminosity performance, 10 GeV e

Linac-ring: higher risk (new concept), higher luminosity performance, 20 GeV e

Preliminary cost estimate is similar. Decision on what to build to supply polarized leptons will be driven by a number of considerations, among them experimental requirements, cost and timeline.

Modest R&D over the next five years will reduce technical risk, especially for linac-ring option.

There are phasing possibilities for both options.

Documents

eRHIC Design