1. 18 th International Spin Physics Symposium Polarized Beams at EIC V. Ptitsyn

2. 18 th International Spin Physics Symposium HERA – first lepton-proton collider Selection of physics results:  precise data on details of the proton structure  the discovery of very high density of sea quarks and gluons present in the proton at low-x  detailed data on electro-weak electron-quark interactions  precision tests of QCD (  s measurements) Double ring collider (6.3 km) Completed its operation in 2007 920 GeV (p) X 27.5 GeV (e -, e + ) 320 GeV center-of-mass energy Longitudinal lepton polarization Superconducting proton ring

3. 18 th International Spin Physics Symposium Physics scope of electron-ion colliders (EIC) after HERA Different Center-of-Mass Energy -> Different kinematic regions Higher Luminosity -> Precision data Polarized beams -> Spin structure of nucleons (still a puzzle!) Ions up to large A -> Gluon physics, Saturation. QCD dynamics in much greater details R. Milner’s plenary talk yesterday

4. 18 th International Spin Physics Symposium Future collider designs Ion ring Electron linear accelerator Ion ring Electron storage ring Ring-ringLinac-ring CMEOn the base of eRHIC ring- ring 30-100 GeVRHIC (BNL) ELIC20-90 GeVCEBAF (JLab) LHeC0.8-2 TeVLHC (CERN) CMEOn the base of eRHIC ERL- based 30-140 GeVRHIC (BNL) LHeC linac based 0.8-2 TeVLHC (CERN)

5. 18 th International Spin Physics Symposium ERL-based eRHIC at BNL  10 GeV electron design energy. Possible upgrade to 20 GeV by doubling main linac length.  5 recirculation passes ( 4 of them in the RHIC tunnel)  Multiple electron-hadron interaction points (IPs) and detectors;  Full polarization transparency at all energies for the electron beam;  Ability to take full advantage of transverse cooling of the hadron beams;  Possible options to include polarized positrons:  compact storage ring;  compton backscattered. Though at lower luminosity. Four recirculation passes PHENIX STAR e-ion detector eRHIC Main ERL (1.9 GeV) Low energy recirculation pass Beam dump Electron source Possible locations for additional e-ion detectors L=2.6 10 33 cm -2 s -1 Polarized p (up to 250 GeV), 3 He Heavy ions (up to Au ions) Electrons: 3-20 GeV

6. 18 th International Spin Physics Symposium Other design options Under consideration also:  Medium Energy EIC at RHIC (MEEIC) Electron energy up to 2-3 GeV. Acceleration done by an ERL linac placed in the RHIC tunnel. It can serve as first stage for following higher electron energy machine. Luminosity ~ 10 32 cm -2 s -1  High energy (up to 20-30 GeV) ERL-based design with all accelerating linacs and recirculation passes placed in the RHIC tunnel. Considerable cost saving design solution. Luminosity exceeds 10 33 cm -2 s -1  Ring-ring design option. Backup design solution which uses electron storage ring. See eRHIC ZDR for more details. The average luminosity is at 10 32 cm -2 s -1 level limited by beam-beam effects. eSTAR ePHENIX ERLs e p e

7. 18 th International Spin Physics Symposium ELIC: EIC at JLab 12 GeV CEBAF Polarized p, D, 3 He Unpolarized ions up to A=208 Polarized e -,e + E p = 30-225 GeV; E ions = 15-100 GeV/n E e = 3-9 GeV Peak L ~ 5.7 10 34 cm -2 s -1 (9 (e) X 225 (p) GeV) Peak L ~ 7. 10 33 cm -2 s -1 (3 (e) X 30 (p) GeV)  “Figure-8” design of ion and lepton storage rings: polarization preservation at all energies.  Very high luminosity approach: moderate bunch intensity, short ion bunches, strong focusing and high bunch repetition rate.  Four interaction regions  The operation compatible with 12 GeV CEBAF operation for fixed target program. ELIC ZDR (Draft)

8. 18 th International Spin Physics Symposium Polarized source development eRHIC: ~ 250 mA average I, 20 nC/bunch MEEIC at RHIC: 50 mA average I, 5 nC/bunch R&D development for a source with large cathode area and, probably, ring like cathode shape is underway (MIT-Bates, E.Tsentalovich) Major issues:  Cathode deterioration by ion back bombardment  Cathode heating -> cooling will be required ELIC: moderate polarized source current demands (1mA in 5  s pulses during the fill) Cathode deterioration measured with various shape of laser spot on the cathode confirms possible advantages of ring-like cathode shape. (E.Tsentalovich) Laser beam forms: small central spot ring-like (+anode bias) ring-like large central spot

9. 18 th International Spin Physics Symposium Electron polarization in ERL eRHIC No problem with depolarizing resonances Spin orientation control at the collision point: –Spin rotators after the electron source (Wien filter, solenoid) –Slight adjustment of energy gain in main and pre-accelerator linacs (keeping the final energy constant) (V.N.Litvinenko)  i,,  i Gun  eSTAR ePHENIX  a is anomalous magnetic moment A,B,C,D are constants depending on general configuration: location of linacs and collision point, number of recirculation passes (n).  f,,  cp Variation of pre-accelerator linac energy:

10. 18 th International Spin Physics Symposium Electron polarization in ELIC The spin control scheme is based on solenoidal snakes and spin rotators (combination of solenoidal magnets and dipoles). Vertical orientation of the spin in the arcs with opposite direction in two halves: –Prevents the depolarization of the electrons ( P eq ~ 90%) –Provides self-polarization of the positrons ( t pol ~ 2h at 7 GeV) Longitudinal spin orientation at all interaction points Challenge: develop spin matched optics to prevent (or minimize) depolarizing effects coming from snakes and rotators. (Next talk by P. Chevtsov) Detector solenoid compensation (?). Spin tune control. spin rotator collision point spin rotator with 90º solenoid snake collision point spin rotator with 90º solenoid snake

11. 18 th International Spin Physics Symposium eRHIC, polarized protons RHIC : - only polarized proton collider in the world. 100 GeV operation so far. Up to 65% polarization achieved. - successful first test with acceleration to 250 GeV in 2006. ~45% polarization - several week operation with 250 GeV protons planned in coming run (February) eRHIC will take favor of existing hardware in RHIC and in the injector chain to accelerate polarized protons up to 250 GeV.

12. 18 th International Spin Physics Symposium Polarized 3 He +2 for eRHIC Larger G factor than for protons RHIC Siberian snakes and spin rotators can be used for the spin control, with less orbit excursions than with protons. More spin resonances. Larger resonance strength. Spin dynamics at the acceleration in the injector chain and in RHIC has to be studied. 3 He +2 p m, GeV2.8080.938 G-4.181.79 E/n, GeV16.2-166.724.3-250  17.3-17725.9-266 |G  72.5-744.946.5-477.7 Max strength for protons W.MacKay and M.Bai

13. 18 th International Spin Physics Symposium Proton/ion polarization in ELIC Figure-8 shape of the storage rings: -eliminates spin sensitivity to energy for all species. No resonance crossing at the acceleration. -the control of spin direction by small spin rotation force:  stabilizing solenoid  controlled vertical orbit distortion (for transverse spin) -For longitudinal spin in all 4 IPs:  two longitudinal axis Siberian Snakes Accelerates of polarized beams of proton, deutrons and 3 He ions. From ELIC ZDR:

14. 18 th International Spin Physics Symposium Summary Polarized beams of electrons, protons and light ions are essential component of the future electron-ion colliders. Polarized electron beam challenges: –High average current polarized source for linac-ring scheme (eRHIC) –Spin matching of complex rotator scheme for ring-ring scheme (ELIC) Polarized proton and light ions beams: –RHIC: state-of-art technology in place and working well; 250 GeV polarized proton run is coming. –ELIC: novel technology (Figure-8). Theoretically well based. Acknowledgments to M.Bai, D.Barber, P.Chevtsov, Ya.Derbenev, V.N.Litvinenko, W.Mackay, T.Roser, E.Tsentalovich.