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

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!

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)x1033 for e-p collisions L = (0.3-1)x1031 for e-Au collisions Polarized electron and proton beams Longitudinal polarization at collision point; 70% 35 nsec minimum separation between bunches

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

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 50-250 GeV Au 100 Gev/u

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

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

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.

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.

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   (0.5-0.9)1033 (0.5-0.9)1031

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.

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

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

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 0.9x1033 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.