Thomas Roser EIC collaboration workshop MIT, April 6, 2007 eRHIC Design eRHIC Schemes R&D Items Cost and Schedule

eRHIC Scope Polarized leptons 3-20 Gev Polarized light ions ( 3 He) 167 Gev/u Heavy ions (Au) Gev/u Polarized protons Gev Electron accelerator RHIC e-e- e+e+ p 70% beam polarization goal

eRHIC Integrated electron-nucleon luminosity of ~ 50 fb -1 over about a decade for both highly polarized nucleon and nuclear (A = 2-208) RHIC beams.  GeV polarized protons  up to 100 GeV/n gold ions  up to 167 GeV/n polarized 3 He ions Two accelerator design options developed in parallel (2004 Zeroth-Order Design Report):  ERL-based design (“Linac-Ring”; presently most promising design): n Superconducting energy recovery linac (ERL) for the polarized electron beam. n Peak luminosity of 2.6  cm -2 s -1 with potential for even higher luminosities. n R&D for a high-current polarized electron source needed to achieve the design goals.  Ring-Ring option: n Electron storage ring for polarized electron or positron beam. n Technologically more mature with peak luminosity of 0.47  cm -2 s -1. Decision on what to build to supply polarized leptons will be driven by a number of considerations, among them experimental requirements, cost and timeline.

ERL-based eRHIC Design  Electron energy range from 3 to 20 GeV  Peak luminosity of 2.6  cm -2 s -1 in electron-hadron collisions;  high electron beam polarization (~80%);  full polarization transparency at all energies for the electron beam;  multiple electron-hadron interaction points (IPs) and detectors;   5 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 e + storage ring 5 GeV - 1/4 RHIC circumference Main ERL (3.9 GeV per pass) 5 mm Compact recirculation loop magnets

ERL-based eRHIC Parameters Electron-Proton CollisionsElectron-Au Collisions High energy setup Low energy setup High energy setup Low energy setup pepeAue e Energy, GeV Number of bunches166 Bunch spacing, ns71 Bunch intensity, (10 9 for Au) Beam current, mA % normalized emittance, πμm Rms emittance, nm  *, x/y, cm Beam-beam parameters, x/y Rms bunch length, cm Polarization, % Peak Luminosity/n, 1.e33 cm -2 s Aver.Luminosity/n, 1.e33 cm -2 s Luminosity integral /week, pb

Ring-Ring eRHIC Design  Based on existing technology  Collisions at 12 o’clock interaction region  10 GeV, 0.5 A e-ring with 1/3 of RHIC circumference (similar to PEP II HER)  Inject at full energy 5 – 10 GeV  Polarized electrons and positrons RHIC 5 – 10 GeV e-ring e-cooling (RHIC II) 5 -10GeV full energy injector

Recirculating NC linac Recirculating SC linac Figure 8 booster synchrotron, FFAG or simple booster Injection of polarized electrons from source Ring optimized for maximum current Top-off eRHIC R-R: Full Energy Injection Options

Ring-Ring eRHIC Parameters High energy setupLow energy setup pepe Energy, GeVGeV Number of bunches Bunch spacingns71 Particles / bunch Beam currentmA % normalized emittance  mm·mrad 155 Emittance  x nm Emittance  y nm  x* m  y* m Beam-beam parameter  x Beam-beam parameter  y Bunch length  z m Polarization% Peak Luminosity10 33, cm -2 s Average Luminosity10 33, cm -2 s Luminosity Integral /week pb

eRHIC Ion Beam  RHIC is the world’s only collider of high-energy heavy ion (for now) and polarized proton beams.  100 GeV proton beams with ~ 65% polarization operational  First test at 250 GeV reached ~ 45% polarization  First high energy stochastic cooling demonstrated in RHIC  Electron cooling under development for RHIC II (x10 luminosity). Also needed/beneficial for eRHIC with same requirements as RHIC II  Presently RHIC operates with 111 bunches of 1.4 x protons. Successful test of 111 bunches of 3 x protons at injection. eRHIC design is 166 bunches of 2 x protons.  Development under way for polarized 3 He beams from the new RHIC ion source EBIS

Interaction Region Design  Yellow ion ring makes 3m vertical excursion.  Design incorporates both normal and superconducting magnets.  Fast beam separation. Besides the interaction point no electron-ion collisions allowed.  Synchrotron radiation emitted by electrons does not hit surfaces of cold magnets (Blue) ion ring magnets (Red) electron beam magnets (Yellow) ion ring magnets Detector

IR Design Schemes Distance to nearest magnet from IP Beam separationMagnets used Hor/Ver beam size ratio Ring-ring, l*=1m 1m Combined field quadrupoles Warm and cold0.5 Ring-ring, l*=3m 3m Detector integrated dipole Warm and cold0.5 Linac-ring5m Detector integrated dipole Warm1  No crossing angle at the IP  Linac-ring: larger electron beta*; relaxed aperture limits ; allows round beam collision geometry (the luminosity gains by a factor of 2.5).  Detector integrated dipole: dipole field superimposed on detector solenoid.

Main R&D Items (other than engineering and costing) Electron beam R&D for ERL-based design: l High intensity polarized electron source (for polarized beams!) n Development of large cathode guns with existing current densities ~ 50 mA/cm 2 with good cathode lifetime. (MIT research proposal) l Energy recovery technology for high energy and high current beams n Thorough beam tests with the BNL test ERL based on the 5-cell cavity studying loss tolerances and the cavity protection systems. l Development of compact recirculation loop magnets n Design, build and test a prototype of a small gap magnet and its vacuum chamber. l Evaluation of electron-ion beam-beam effects, including the kink instability and e-beam disruption n Realistic beam-beam simulations. Electron beam R&D for the ring-ring design: l No major R&D items Main R&D items for ion beam for both designs: l Polarized 3 He production (EBIS) and acceleration n Develop EBIS as spin-preserving ionizer of optically pumped pol. 3 He gas n Evaluation of depolarization due to high anomalous magnetic moment of pol. 3 He beams during acceleration in AGS and RHIC

Other R&D R&D for specific experimental programs: High precision ion beam polarimeter Improve absolute polarization accuracy from about 5% to 1% R&D to further increase eRHIC luminosity: Increase number of ion bunches from 166 to 333 Electron clouds with 30 ns ion bunch spacing (LHC has 25 ns bunch spacing) Injection kicker development Higher current of ERL Optical stochastic cooling of high energy proton beam Proof of principal experiment proposed at Bates Beam-beam compensation The focusing effect of the colliding electron beam on the ion beam could be compensated with ion-ion collisions

Ring-ring preliminary cost estimate (2007$) Electron ring : 132 M Interaction region 9 M Injector (warm recirculating linac, incl. source): 113 M Installation: 16 M Civil construction: 21 M Total: 291 M With PED/EDIA (20%), Contingency (30%) and G&A (15%): Total Equipment Cost (TEC): 523 M Detector allowance: 103 M Pre-ops, R&D: 72 M Total Project Cost (TPC): ~ 700 M

Linac-ring preliminary cost estimate (2007$) 4 GeV superconducting linac incl. source: 111 M 5 pass recirculation loops (5 x ~15M): 77 M Interaction region: 9 M Installation: 26 M Civil construction: 21 M Cryogenics: 41 M Switch yards: 21 M Positron capability: 15 M Total: 321 M With PED/EDIA (20%), Contingency (30%) and G&A (15%): Total Equipment Cost (TEC): 577 M Detector allowance: 103 M Pre-ops, R&D: 72 M Total Project Cost (TPC): ~ 750 M

Straw-man technically driven schedule in 2007$ FY10FY11FY12FY13FY14FY15FY16FY17Total R&D57517 CDR33 PED/EDIA Construction Pre-ops TPC Incremental operations costs: ~ 50 M (2007$)

Summary Two versions for eRHIC have been developed: Ring-ring: lower risk (ready to go), lower luminosity performance, 10 GeV e Linac-ring: higher risk (new concept), higher luminosity performance, 20 GeV e Preliminary cost estimate is similar. Decision on what to build to supply polarized leptons will be driven by a number of considerations, among them experimental requirements, cost and timeline. Modest R&D over the next five years will reduce technical risk, especially for linac-ring option. There are phasing possibilities for both options.