Electron Injector Full energy injector provides 5 10

Electron Injector • Full energy injector provides 5 -10 n. C bunches at up to 2 Hz rate with alternating (up and down) spin. • The e. RHIC polarized electron gun has been designed based on experience from both SLC PES high charge gun and JLab inverted guns. • 2. 856 GHz 400 Me. V pre-injector has been simulated. Meets the requirements. • Spin transparent Rapid Cycling Synchrotron is used for acceleration from 0. 4 Ge. V up to 18 Ge. V. • High lattice quasi-symmetry with spin-transparent straight sections suppress intrinsic depolarizing resonance during the ramp • 100 -200 ms acceleration ramp is sufficiently fast to cross resonances preserving the polarization • Swap-out injection into the storage ring is used to maximize the beam polarization. Injection/accumulation is done in longitudinal plane to avoid transient beam-beam effects. 1 Cathode preparation system HV DC Gun e. RHIC polarized gun e. RHIC swap-out injection scheme

Electron Storage Ring D 2 0. 59 m • High intensity storage ring (Ie up to 2. 5 A) based on accelerator technologies of B-factories and HERA D 1 3. 25 m • 10 MW of synchrotron radiation (selfimposed limit) at 10 -18 Ge. V • Composed of six FODO arcs with 60º /cell for 5 -10 Ge. V and 90º /cell for 18 Ge. V • Super-bends for 5 -10 Ge. V for emittance and damping decrement control • Spin rotators based on interleaved solenoidal and dipole magnets provide the longitudinal polarization in all energy range (5 -18 Ge. V) RCS Storage Ring 2 D 1 3. 25 m e. RHIC superbend

e. RHIC Layout in Tunnel Straight Section 3

Increasing proton intensity and repetition rate Present RHIC e. RHIC nominal Beam current, m. A 330 1000 Bunch frequency, MHz 9. 4 98. 5 Peak current, A 12 24 Proton parameters In-situ copper coating of existing stainless steel beam pipe to reduce cryo-load from resistive heating. The accepted level of e. RHIC proton current is similar to one in the HL-LHC upgrade. Electron cloud • Beam scrubbing is an efficient tool based on LHC experience • But additional remedies may be needed to reduce SEY. Under evaluation: • Amorphous C coating (using the tooling developed for Cu-coating) • Laser-engineered grooving Magnetron mole for coating long narrow tubes has been designed and built. Required hardware upgrades: • New injection kickers (<18 ns rise time) • RF system upgrade to incorporate bunch splitting and bunch compression 4

Polarized light ions p 3 He+2 d G 1. 79 -4. 18 -0. 143 |Gg | 45. 5 -525. 5 48. 5 -818 1. 6 -20. 9 Polarized d with/without tune jump Polarized 3 He g • Polarized deuteron acceleration has been explored : • The imperfection resonances can be overcome by a solenoid partial snake • The intrinsic resonances can be overcome with modest tune jump • Longitudinal polarization can be produced at particular energies, near integer Gg, by using helical or solenoidal fields, or by vertical orbit excursions • Polarized 3 He+2 has been thoroughly simulated • 6 Snakes per ring (instead of present 2) are required for polarization preservation • AC dipole in Booster + stronger AGS Snakes will ensure the polarization through injector chain • Test of polarized 3 He acceleration through the injector chain in 2021 5

Hadron Cooling and On-Energy Injection Alternative • Strong hadron cooling at the proton store energy (275 Ge. V) presents the convenience of the long experimental stores, maximizing average luminosity. • Different methods of strong hadron cooling are being explored conceptually, by simulations and experimentally Goal: tcool < 1 h at 275 Ge. V Micro-bunched electron beam cooling with several plasma amplification stages (SLAC/BNL) • See F. Willeke’s and I. Petrushina’s talks • Alternative to the hadron cooling at the store energy is on-energy hadron injector scheme. • The scheme fully employs both of the existing RHIC rings: § § Yellow RHIC ring is used as the e. RHIC hadron Storage ring Blue RHIC ring is used as the e. RHIC hadron Accelerator ring • The stored hadron beam will be replaced with 1 -1. 5 h our intervals, with average luminosity >90% of the peak one. • The peak luminosity of 1034 cm-2 s-1 in this scheme can be achieved by the cooling at low energies: in AGS (several Ge. V) and/or at the e. RHIC hadron injection energy (25 Ge. V). 6

On-Going R&D Program Supported by various funding: BNL LDRDs, DOE , NY State, SBIRs Done in collaboration with JLab, Cornell, Fermilab, SLAC, LBNL, … Component Development • Crab Cavity design development and prototyping • IR magnet development and prototyping • HOM damping for RF structure development • Variable coupling high power forward power couplers development • Effective in-situ Cu and amorphous C coating of the beam pipe Instrumented accelerator magnet • High average current electron gun development • Polarized 3 He source In-situ coppercoated beam pipe • Bunch by bunch polarimetry Accelerator Physics R&D • Strong hadron cooling development, simulation and experimental • ERL development for strong hadron cooling (see S. Brooks’s talk) Crab cavity • Study of residual crab cavity effect on beam emittance Crabbed beam dynamics 7

Current Status of e. RHIC and Path forward of EIC • The p. CDR design has gone through a series of design and cost reviews in last two years • The accelerator design team continues to tweak some of design aspects with the purpose of minimizing the construction cost and mitigating technological risks • The p. CDR document has been updated this summer From T. Hallman (the Associate Director for Nuclear Physics of the DOE SC): • A Mission Need Statement for an EIC has been approved by DOE • DOE is moving forward with a request for CD-0 (approve Mission Need) • An Independent Cost Review (ICR) Exercise mandated by DOE rules for projects of the projected scope of the EIC is very far along • DOE has organized a panel to assess options for siting and consideration of “best value” between the two proposed 8 concepts

Summary • The design of the electron-ion collider e. RHIC at BNL is based on the existing hadron RHIC complex and a new storage ring based electron accelerator. It completely re-uses the existing infrastructure. • The design relies for the most part on established accelerator technology. • The pre-conceptual design of the e. RHIC has been worked out. The detailed p. CDR has been issued in July 2018. Recent design updates have been included this summer. • The e. RHIC design fully satisfies the EIC physics requirements from the EIC White paper. The luminosity exceeding 1034 cm-2 s-1 can be achieved. • The R&D program is underway which addresses hadron cooling techniques, aspects of SRF technology, beam-beam effects, pipe coating, high-current ERL and others technologies for the e. RHIC. • There are indications that the CD-0 approval for the electron-ion collider may come in the near future. 9

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