1. eRHIC with Self-Polarizing Electron Ring
V.Ptitsyn, J.Kewisch, B.Parker, S.Peggs, D.Trbojevic, BNL, USA D.E.Berkaev, I.A.Koop, A.V.Otboev, Yu.M.Shatunov, BINP, Russia C.Tschalaer, J.B. van der Laan, F.Wang, MIT-Bates, USA D.P.Barber, DESY, Hamburg, Germany

2. The EIC w.r.t. Other Experimental Facilities
Large luminosity and high CM Energy makes EIC unique!
TESLA-N
Variable CM energy enhances
its versatility!

3. EIC Objectives e-p and e-ions collisions
5-10 GeV electrons; Gev protons; 100 Gev/u Au
Luminosity:
L = (0.3-1)x for e-p collisions
L = (0.3-1)x for e-Au collisions
Polarized electron and proton beams
Longitudinal polarization at collision point; 70%
35 nsec minimum separation between bunches

4. Polarized Proton in RHIC
Absolute Polarimeter (H jet)
RHIC pC Polarimeters
BRAHMS & PP2PP (p)
PHENIX (p)
STAR (p)
Siberian Snakes
Spin Rotators
Partial Siberian Snake
Pol. Proton Source
500 mA, 300 ms
Strong AGS Snake
2  1011 Pol. Protons / Bunch
e = 20 p mm mrad
LINAC
BOOSTER
AGS
200 MeV Polarimeter
AGS Internal Polarimeter
Rf Dipoles
AGS pC Polarimeters

5. eRHIC collider layout e p e-ring is 5/16 of RHIC ring
Collisions at one IP
28 MHz collision rate
Unpolarized electron source
Electron beam polarization by the synchrotron radiation
e-ring lattice based on ”superbend” magnets
2GeV (5GeV) e
2-10 GeV
IP12 p
RHIC
p GeV
Au 100 Gev/u

6. Superbend magnet B,T Issues: 2 0.2 10GeV 5GeV 10GeV 5GeV
The desired balance:
short polarization time at the
acceptable level of synchrotron
radiation losses
Flexible control of the beam emittance
0.57
Issues:
Accomodation of radiated power (7MW radiated at 10 GeV)
Orbit lengthening versus beam energy
0.15m 3m

7. Polarization time with superbend
Magnet bending field scaled proportionally with energy
The superbend control of polarization time.
8-15min polarization time is achievable.

8. Luminosity and beam-beam limits
Reasonably achievable values:
0.05
0.005
Round beams:
nx=ny , bx=by for electrons
Matching of the e and p beam sizes is crucial.

9. Beam emittance control
Electron emittance versus electron energy
for different superbend settings
Ee=10GeV
e-cool zone
Ee=5GeV
Required normalized emittances for Au: 5-8 Pi mm*mrad at 5-10 GeV electron energies;
The cooling is required.
Cooling of the proton beam is required for proton energies below 200 GeV
Electron cooling system for RHIC is being developed.

10. Main beam parameters 360 (0.5-0.9)1033 (0.5-0.9)1031 Parameters
e-ring
ion ring p Au
C, m
1022
3833
E, GeV
5–10
250
100/u nb 96
360 Nb
11011
1109
I, A
erms,mm rad
b*, cm
s*, mm x
0.45
45–25 10
0.07–0.05
0.05
17–9 27
0.005
L, cm-2 s-1
( )1033
( )1031

11. Depolarization from ring imperfections in the e-ring
Polarization issues
Depolarization from ring imperfections in the e-ring
0.5mm rms closed orbit error assumed.
The correction scheme similar to the one used at HERA should solve the problem.
Fast polarimeter for the on-line spin resonance corrections.
The possibility to accelerate polarized light ions: deutrons, tritium, 3He, 19F (E.Courant).
The polarized sources development is required.

12. IR Design
Horizontal separation scheme
Vertical separation scheme
IR development proceeds in close link with the detector design
Detector background and protection from synchrotron radiation issues

13. Spin rotator e-ring: solenoidal spin rotator -> simplest solution
Perfect longitudinal polarization at 7.5GeV
~15% reduction at 5 or 10 GeV.
Spin transparency conditions on optics
Rotator design n
solenoid
solenoid n
quads
p-ring: Helical spin rotator like being used already at two RHIC experiments

14. Summary:
The design is based on the construction of a self-polarizing electron ring.
Polarized e-p and unpolarized e-ion beam collisions in the center of mass energy range of Gev and at luminosities up to 0.9x1033 cm-2s-1 for e-p and 0.9x1031 cm-2s-1 for e-Au collisions.
The electron polarization time of 8-15min is achieved with superbend magnets.
The collider design could be realized using the present level of the accelerator technology.