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! Variable CM energy enhances its versatility! TESLA-N

3. EIC Objectives  e-p and e-ions collisions  5-10 GeV electrons; 25-250 Gev protons; 100 Gev/u Au  Luminosity:  L = (0.3-1)x10 33 for e-p collisions  L = (0.3-1)x10 31 for e-Au collisions  Polarized electron and proton beams  Longitudinal polarization at collision point; 70%  35 nsec minimum separation between bunches

4. BRAHMS & PP2PP (p) STAR (p) PHENIX (p) AGS LINAC BOOSTER Polarized Proton in RHIC Pol. Proton Source 500  A, 300  s Spin Rotators Partial Siberian Snake Siberian Snakes 200 MeV Polarimeter AGS Internal Polarimeter Rf Dipoles RHIC pC Polarimeters Absolute Polarimeter (H jet) 2  10 11 Pol. Protons / Bunch  = 20  mm mrad AGS pC Polarimeters Strong AGS Snake

5. eRHIC collider layout 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 p e 2GeV (5GeV) 2-10 GeV IP12 RHIC p 50-250 GeV Au 100 Gev/u

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

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  Round beams:  x = y,  x =  y for electrons  Matching of the e and p beam sizes is crucial. Reasonably achievable values: 0.05 0.005

9. Electron emittance versus electron energy for different superbend settings E e =10GeV E e =5GeV e-cool zone 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. Beam emittance control

10. Main beam parameters Parameterse-ring ion ring pAu C, m10223833 E, GeV5–10250100/u nbnb 96 360 NbNb 1  10 11 1  10 9 I, A  rms,mm  rad  *, cm  *, mm  0.45 45–25 10 0.07–0.05 0.05 0.45 17–9 27 0.07–0.05 0.005 L, cm -2 s -1 (0.5-0.9)  10 33 (0.5-0.9)  10 31

11. Polarization issues 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, 3 He, 19 F (E.Courant). The polarized sources development is required. Depolarization from ring imperfections in the e-ring

12. Horizontal separation scheme Vertical separation scheme IR Design 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 n solenoid quads n Rotator design 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 30-100 Gev and at luminosities up to 0.9x10 33 cm -2 s -1 for e-p and 0.9x10 31 cm -2 s -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.