eRHIC Design
eRHIC Schemes
R&D Items
Cost and Schedule
Thomas Roser
EIC collaboration workshop
MIT, April 6, 2007
eRHIC Scope
RHIC
Electron accelerator
p
Polarized leptons
3-20 Gev
Polarized protons
50-250 Gev
ee+
70% beam polarization goal
Heavy ions (Au)
50-100 Gev/u
Polarized light ions (3He)
167 Gev/u
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.
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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):
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ERL-based design (“Linac-Ring”; presently most promising design):
 Superconducting energy recovery linac (ERL) for the polarized electron beam.
33 cm-2s-1 with potential for even higher luminosities.
 Peak luminosity of 2.6  10
 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.
33 cm-2s-1.
 Technologically more mature with peak luminosity of 0.47  10
Decision on what to build to supply polarized leptons will be driven by a number of
considerations, among them experimental requirements, cost and timeline.
e-cooling
(RHIC II)
PHENIX
Main ERL (3.9 GeV per pass)
Peak Luminosity, 1033 cm-2s-1
ERL-based eRHIC Design
3
3GeV(e)-250GeV(p)
2
1.5
1
0.5
3GeV(e)-50GeV(p)
20GeV(e)-50GeV(p)
0
20
30
40
50
STAR
60
70
80
90 100 110 120 130 140 150
Center-Of-Mass Energy, GeV
e+ storage ring
Four e-beam 5 GeV - 1/4 RHIC
circumference
passes

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
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


20GeV(e)-250GeV(p)
2.5
Compact recirculation
loop magnets
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.
5 mm
5 mm
5 mm
5 mm
ERL-based eRHIC Parameters
Electron-Proton Collisions
Electron-Au Collisions
High energy
setup
Low energy
setup
High energy
setup
p
e
p
e
Au
e
Au
e
Energy, GeV
250
20
50
3
100
20
50
3
Number of bunches
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
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
b*, x/y, cm
26
200
26
150
26
200
26
60
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
95% normalized emittance, πμm
Beam-beam parameters, x/y
166
166
Low energy
setup
166
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
5 – 10 GeV e-ring
5 -10GeV full
energy injector
RHIC
e-cooling
(RHIC II)

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
eRHIC R-R: Full Energy Injection Options
Polarized Electron
200 MeV
Source
Copper Linac, SLAC type cavities
Polarized Electron
200 MeV SC Linac, Tesla type cavities
Source
10 GeV
8 GeV
6.7 GeV
2 GeV
4 GeV
2 GeV
3.3 GeV
10 GeV
6 GeV
8.3 GeV
Positron Source 4 GeV
10
1.7 GeV
200 MeV
200 MeV
0
5 GeV
50
Positron Source 3.3 GeV
100
150
200
250
275 m
Recirculating NC linac
0
10
50
100
150
200
250
275 m
Recirculating SC linac
Extraction
5 - 10 GeV
• Injection of polarized electrons from
source
• Ring optimized for maximum current
Injection
0.5 GeV
Positron Source
0
10
50
100
Polarized Electron
Source, 20 MeV
150 m
• Top-off
Figure 8 booster synchrotron,
FFAG or simple booster
Ring-Ring eRHIC Parameters
High energy setup
Energy, GeV
GeV
Number of bunches
Low energy setup
p
e
p
e
250
10
50
5
165
55
165
55
71
71
71
71
Bunch spacing
ns
Particles / bunch
1011
1.00
2.34
1.49
0.77
Beam current
mA
208
483
315
353
95% normalized emittance
p mm·mrad
15
Emittance ex
nm
9.5
53.0
15.6
130
Emittance ey
nm
9.5
9.5
15.6
32.5
bx*
m
1.08
0.19
1.86
0.22
by*
m
0.27
0.27
0.46
0.22
Beam-beam parameter xx
0.015
0.029
0.015
0.035
Beam-beam parameter xy
0.0075
0.08
0.0075
0.07
5
Bunch length sz
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
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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.
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Synchrotron radiation emitted by electrons does
not hit surfaces of cold magnets
(Red) electron
beam magnets
(Blue) ion ring
magnets
Detector
(Yellow) ion ring magnets
IR Design Schemes
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Distance to nearest
magnet from IP
Beam separation
Magnets used
Hor/Ver beam
size ratio
Ring-ring,
l*=1m
1m
Combined field
quadrupoles
Warm and cold
0.5
Ring-ring,
l*=3m
3m
Detector
integrated dipole
Warm and cold
0.5
Linac-ring
5m
Detector
integrated dipole
Warm
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!)
2
 Development of large cathode guns with existing current densities ~ 50 mA/cm 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:
3
 Polarized He production (EBIS) and acceleration
3
 Develop EBIS as spin-preserving ionizer of optically pumped pol. He gas
3
 Evaluation of depolarization due to high anomalous magnetic moment of pol. He
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$)
Electron ring
:
132 M
Interaction region
9M
Injector (warm recirculating linac, incl. source):
113 M
Installation:
16 M
Civil construction:
21 M
----------------------------------------------------------------------------------------Total:
291 M
----------------------------------------------------------------------------------------With PED/EDIA (20%), Contingency (30%) and G&A (15%):
Total Equipment Cost (TEC):
523 M
Detector allowance:
103 M
Pre-ops, R&D:
72 M
----------------------------------------------------------------------------------------Total Project Cost (TPC):
~ 700 M
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Linac-ring preliminary cost estimate (2007$)
4 GeV superconducting linac incl. source:
111 M
5 pass recirculation loops (5 x ~15M):
77 M
Interaction region:
9M
Installation:
26 M
Civil construction:
21 M
Cryogenics:
41 M
Switch yards:
21 M
Positron 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 M
Pre-ops, R&D:
72 M
----------------------------------------------------------------------------------------------Total Project Cost (TPC):
~ 750 M
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Straw-man technically driven schedule in 2007$
FY10
FY11
FY12
R&D
5
7
5
CDR
3
PED/EDIA
FY13
FY14
FY15
31
Total
17
62
23
62
115
103
144
Pre-ops
8
FY17
3
Construction
TPC
FY16
38
67
84
Incremental operations costs: ~ 50 M (2007$)
103
144
144
111
564
16
35
51
161
146
752
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.