eRHIC DESIGN UPDATE ∗ C. Montag † , G. Bassi, J. Beebe-Wang, J.S. Berg, M. Blaskiewicz, A. Blednykh, J.M. Brennan, S.J. Brooks, K.A. Brown, K.A. Drees, A.V. Fedotov, W. Fischer, D.M. Gassner, Y. Hao, A. Hershcovitch, C. Hetzel, D. Holmes, H. Huang, W.A. Jackson, J. Kewisch, Y. Li, C. Liu, H. Lovelace III, Y. Luo, F. Meot (F. Méot), M.G. Minty, R.B. Palmer, B. Parker, S. Peggs, V. Ptitsyn, V.H. Ranjbar, G. Robert-Demolaize, S. Seletskiy, V.V. Smaluk, K.S. Smith, S. Tepikian, P. Thieberger, D. Trbojevic, N. Tsoupas, W.-T. Weng, F.J. Willeke, H. Witte, Q. Wu, W. Xu, A. Zaltsman, W. Zhang, Brookhaven National Laboratory, Upton, NY, U.S.A., E. Gianfelice-Wendt, Fermi National Accelerator Laboratory, Batavia, IL, U.S.A., Y. Cai, Y. Nosochkov, SLAC National Accelerator Laboratory, Menlo Park, CA, U.S.A. Abstract The future electron-ion collider (EIC) aims at an electron- proton luminosity of 10 33 to 10 34 cm −2 sec −1 and a center-of- mass energy range from 20 to 140GeV. The eRHIC design has been continuously evolving over a couple of years and has reached a considerable level of maturity. The concept is generally conservative with very few risk items which are mitigated in various ways. INTRODUCTION The proposed electron-ion collider eRHIC will collide polarized electron and polarized light (proton, deuteron, or 3 He) or unpolarized heavy ion beams up to uranium at center- of-mass energies ranging from 20 to 140GeV (electron- proton equivalent). The projected e-p luminosity of the facility reaches 10 34 cm −2 sec −1 , thus meeting all the require- ments laid out in the U.S. Nuclear Physics community’s White Paper [1]. The machine design is based on the ex- isting RHIC facility with its 3.8 km circumference tunnel and its hadron injector complex. The eRHIC hadron beam will be stored in the superconducting “Yellow” RHIC ring, while a new electron storage ring and a rapid cycling syn- chrotron [2] will be added in the same tunnel. Table 1 lists the main electron-proton parameters of eRHIC at a center- of-mass energy of 105GeV, where the highest luminosity is reached. INTERACTION REGION DESIGN The eRHIC interaction region [3] is based on supercon- ducting magnets to focus the beams at the interaction point, with vertical β-functions as low as a few centimeters. The peak magnetic fields of these quadrupoles, defined here as B peak = R × g, where R and g denote the aperture radius and the gradient, respectively, do not exceed 6T. There- fore, all magnets can be built using NbTi superconductors. Furthermore, only a few magnets need to be built as col- lared magnets, while the majority can be manufactured using direct-wind technology. ∗ Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. † montag@bnl.gov Table 1: eRHIC Electron-Proton Parameters at 105GeV Center-of-Mass Energy proton electron no. of bunches 1160 energy [GeV] 275 10 bunch intensity [10 10 ] 6.9 17.2 beam current [A] 1.0 2.5 ϵ RMS hor./vert. [nm] 9.6/1.5 20.0/1.2 β ∗ x , y [cm] 90/4 43/5 b.-b. param. hor./vert. 0.014/0.007 0.073/0.100 σ s [cm] 6 2 σ dp/p [10 −4 ] 6.8 5.8 τ IBS long./transv. [h] 3.4/2.0 N/A L [10 33 cm −2 sec −1 ] 10.05 Separation of the two beams is accomplished by a 25 mrad crossing angle. A spectrometer dipole on the forward side of the ±4.5m long central detector is equipped with detec- tor components to increase the forward acceptance of the detector. The large aperture of this magnet is shared by both the eletron and the hadron beam. A bucking coil shields the electron beam from the magnetic field of the spectrometer. A dipole magnet on the forward side of the detector sepa- rates the hadron beam from the ±4 mrad forward neutron cone which is then detected in the zero degree calorimeter. The aperture of the electron quadrupoles on the rear side is large enough to accommodate the synchrotron radiation fan generated from a 12.5σ electron beam in the quadrupoles on the forward (incoming) side of the detector. Luminosity monitoring is based on detection of Bethe-Heitler photons generated in the interaction. Figure 1 shows a schematic view of the eRHIC interaction region. ELECTRON STORAGE RING The electron storage ring is based on FODO cells using conventional room-temperature magnets. The bending sec- tions are realized as so-called super-bends, where each dipole is actually comprised of three individual magnets - two long dipoles with a short magnet in-between. The purpose of this arrangement is to generate additional synchrotron radiation damping and enhance the equilibrium emittance at energies North American Particle Acc. Conf. NAPAC2019, Lansing, MI, USA JACoW Publishing ISBN: 978-3-95450-223-3 ISSN: 2673-7000 doi:10.18429/JACoW-NAPAC2019-MOYBA4 MOYBA4 18 Content from this work may be used under the terms of the CC BY 3.0 licence (© 2019). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI 01: Circular and Linear Colliders FERMILAB-CONF-19-859-AD This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.