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)
3GeV(e)-250GeV(p) 20GeV(e)-250GeV(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
3GeV(e)-50GeV(p) 20GeV(e)-50GeV(p)
3GeV(e)-250GeV(p) 20GeV(e)-250GeV(p)
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.