1. eRHIC design status V.Ptitsyn for the eRHIC design team

2. V.PtitsynEIC Collaboration Meeting, 12/07/07 eRHIC Scope Polarized leptons 3-10 Gev (20GeV) Polarized light ions ( 3 He) 167 Gev/u Heavy ions (Au) 50-100 Gev/u Polarized protons 50-250 Gev Electron accelerator RHIC e-e- e+e+ p 70% beam polarization goal

3. V.PtitsynEIC Collaboration Meeting, 12/07/07 ERL-based eRHIC Design  Peak luminosity of 2.6  10 33 cm -2 s -1 in electron-hadron collisions;  high electron beam polarization (~80%) and full polarization transparency at all energies for the electron beam;  multiple electron-hadron interaction points (IPs) and detectors;   3 meter “element-free” straight section(s) for detector(s);  ability to take full advantage of electron cooling of the hadron beams;  easy variation of the electron bunch frequency to match the ion bunch frequency at different ion energies. PHENIX STAR e-cooling (RHIC II) Four e-beam passes Main ERL (1.9 GeV per pass) Low energy pass

4. ERL-based eRHIC Parameters High energy setupLow energy setup pepe Energy, GeV25010503 Number of bunches166 Bunch spacing, ns71 Bunch intensity, 10 11 21.22.01.2 Beam current, mA420260420260 Normalized 95% emittance, p mm.mrad64606570 Rms emittance, nm3.841916.5  *, x/y, cm 26252630 Beam-beam parameters, x/y0.0150.590.0150.47 Rms bunch length, cm201 1 Polarization, %70807080 Peak Luminosity, 1.e33 cm -2 s -1 Aver.Luminosity, 1.e33 cm -2 s -1 2.60.53 0.870.18 Luminosity integral /week, pb -1 530105

5. Coherent Electron Cooling (V.N. Litvinenko, Ya.S. Derbenev) of high energy protons may be possible with present FEL and ERL technology Luminosity with cooling

6. V.PtitsynEIC Collaboration Meeting, 12/07/07 Main R&D Items Electron beam R&D for ERL-based design: –High intensity polarized electron source Development of large cathode guns with existing current densities ~ 50 mA/cm 2 with good cathode lifetime. –Energy recovery technology for high power beams 5-cell cavity; BNL test ERL; loss protection; instabilites. –Development of compact recirculation loop magnets Design, build and test a prototype of a small gap magnet and its vacuum chamber. –Evaluation of electron-ion beam-beam effects, including the kink instability and e-beam disruption Y.Hao’s presentation. Main R&D items for ion beam: –Polarized 3 He production (EBIS) and acceleration –166 bunches

7. V.PtitsynEIC Collaboration Meeting, 12/07/07 PES design items -Large area cathodes (diameter > 1cm) -Ring-like cathode, to minimize ion bombardment damage. -Active cooling, to accommodate ~100W of heating load from laser power -Multiple gun approach. RF-combiner. (V.N.Litvinenko)

8. V.PtitsynEIC Collaboration Meeting, 12/07/07 Polarized source R&D  Recent JLab polarized source studies and advances. ~ 1mA highly polarized average current demonstrated.  MIT-Bates group (E.Tsentalovich et al) has started the R&D study for high intensity (50 mA goal) polarized gun for eRHIC: Phase I:  Gun simulation (including ring geometry)  Design of the cathode with active cooling Phase II:  Design and construction of the gun  Design and construction of the beam line  Lifetime measurements at different currents Time scale: ~3 years

9. V.PtitsynEIC Collaboration Meeting, 12/07/07 Recirculating passes Compact magnet loops (V.N.Litvinenko et al) FFAG (D.Trbojevic et al) 5 mm Smaller total number of magnet Larger synchrotron radiation losses Approved LDRD for magnet development (2 years) Separate loops Small aperture magnets

10. R&D ERL Commissioning. Start at 2009 test of high current (several hundred Amps) high brightness ERL operation 5-cell cavity SRF ERL high current beam stability highly flexible lattice 704 MHz SRF gun test

11. V.PtitsynEIC Collaboration Meeting, 12/07/07 Linac optics supercavity QFQDQF supercavity 12.7 m cell QD Supercavity: two 700 MHz cavities with up to 19 Mev gain/cavity + 2.1 GHz cavity Total energy gain per supercavity ~ 34 MeV Optics solution with constant gradient linac lattice

12. V.PtitsynEIC Collaboration Meeting, 12/07/07 Longitudinal transport 3 rd harmonic cavities are used in both main and pre-accelerator linacs R 56 =500 mm R 56 =20 mm z, mm Isochronous conditions for recirculating passes

13. V.PtitsynEIC Collaboration Meeting, 12/07/07 Other design options  Ring-ring design option Based on existing technology Collisions at 12 o’clock interaction region 10 GeV, 0.5 A e-ring with 1/3 of RHIC circumference Injection at full energy 5 – 10 GeV Polarized electrons and positrons e-p peak luminosity at 4.4E32 cm -2 s -1 (with IR quads at 1m from the IR)  ERL-based design for smaller energy All components are located inside the existing RHIC tunnel, including the source, pre-accelerator, 0.5 GeV energy recovery linac, several short and long recirculation loops. Possible electron energy up to 2-3 GeV. This can be done if there is exciting physics.

14. V.PtitsynEIC Collaboration Meeting, 12/07/07 Summary We continue the accelerator design work on various aspects of the ERL-based design of eRHIC, which presently aims to provide e-p average luminosity at 10 33 cm -2 s -1 level. Important eRHIC R&D subjects, such as polarized source development, ERL test facility and compact magnet design, are supported by financing. So, we can expect advances on those directions in coming 2-3 years. Other considered design options: ring-ring design (eRHIC ZDR), smaller electron energy ERL-based design.