Polarized Beams at EIC

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

2. HERA – first lepton-proton collider 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 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 (as measurements) 18th International Spin Physics Symposium

3. 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 18th International Spin Physics Symposium

4. Future collider designs Electron linear accelerator Electron storage ring Ion ring Ion ring Ring-ring Linac-ring 18th International Spin Physics Symposium

5. ERL-based eRHIC at BNL e-ion detector Possible locations for additional e-ion detectors eRHIC PHENIX Main ERL (1.9 GeV) STAR Beam dump Low energy recirculation pass Four recirculation passes Electron source Polarized p (up to 250 GeV), 3He Heavy ions (up to Au ions) Electrons: 3-20 GeV • 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. L=2.6 1033 cm-2 s-1 18th International Spin Physics Symposium

6. Other design options ePHENIX eSTAR • 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 ~ 1032 cm-2s-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 1033 cm-2s-1 • Ring-ring design option. Backup design solution which uses electron storage ring. See eRHIC ZDR for more details. The average luminosity is at 1032 cm-2s-1 level limitedby beam-beam effects. e ERLs e p 18th International Spin Physics Symposium

7. ELIC: EIC at JLab Ep = 30-225 GeV; Eions = 15-100 GeV/n Ee = 3-9 GeV Peak L ~ 5.7 1034 cm-2 s-1 (9 (e) X 225 (p) GeV) Peak L ~ 7. 1033 cm-2 s-1 (3 (e) X 30 (p) GeV) Polarized p, D, 3He Unpolarized ions up to A=208 Polarized e-,e+ • “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. 12 GeV CEBAF ELIC ZDR (Draft) 18th International Spin Physics Symposium

8. Polarized source development • eRHIC: ~ 250 mA average I, 20 nC/bunch • MEEIC at RHIC: 50 mA average I, 5 nC/bunch Laser beam forms: small central spot ring-like (+anode bias) ring-like large central spot • 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 Cathode deterioration measured with various shape of laser spot on the cathode confirms possible advantages of ring-like cathode shape. (E.Tsentalovich) ELIC: moderate polarized source current demands (1mA in 5ms pulses during the fill) 18th International Spin Physics Symposium

9. Electron polarization in ERL eRHIC Gun • 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) Dg Dg 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). gi,,ji Variation of pre-accelerator linac energy: ePHENIX gf,,jcp eSTAR 18th International Spin Physics Symposium

10. Electron polarization in ELIC spin rotator spin rotator spin rotator with 90º solenoid snake collision point collision point collision point collision point spin rotator with 90º solenoid snake spin rotator spin rotator • 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 ( Peq ~ 90%) • Provides self-polarization of the positrons ( tpol ~ 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. 18th International Spin Physics Symposium

11. eRHIC, polarized protons Absolute Polarimeter (H jet) RHIC pC Polarimeters Siberian Snakes Spin flipper PHENIX (p) STAR (p) Spin Rotators (longitudinal polarization) Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake LINAC BOOSTER Helical Partial Siberian Snake Pol. H- Source AGS 200 MeV Polarimeter AGS Polarimeters Strong AGS Snake 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. 18th International Spin Physics Symposium

12. Polarized 3He+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. W.MacKay and M.Bai Max strength for protons 18th International Spin Physics Symposium

13. Proton/ion polarization in ELIC Accelerates of polarized beams of proton, deutrons and 3He ions. From ELIC ZDR: • 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 18th International Spin Physics Symposium

14. 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. 18th International Spin Physics Symposium