BNL, Upton, Long Island, New York, USA
Fermilab, Batavia, Illinois, USA
FRIB, East Lansing, Michigan, USA
The Electron-Ion Collider (EIC) is being envisioned as the next facility to be constructed by the DOE Nuclear Physics program. Brookhaven National Laboratory is proposing eRHIC, a facility based on the existing RHIC complex as a cost effective realization of the EIC project with a peak luminosity of 1034 cm-2 sec-1. An electron storage ring with an energy range from 5 to 18 GeV will be added in the existing RHIC tunnel. A spin-transparent rapid-cycling synchrotron (RCS) will serve as a full-energy polarized electron injector. Recent design improvements include reduction of the IR magnet strengths to avoid the necessity for Nb3Sn magnets, and a novel hadron injection scheme to maximize the integrated luminosity. We will provide an overview of this proposed project and present the current design status.
BNL, Upton, Long Island, New York, USA
The design effort for the electron-ion collider eRHIC has concentrated on electron-proton collisions at the highest luminosities over the widest possible energy range. The present design also provides for electron-nucleon peak luminosities of up to 4.7·1033 cm-2s−1 with strong hadron cooling, and up to 1.7·1033 cm-2s−1 with stochastic cooling. Here we discuss the performance limitations and design choices for electron-ion collisions that are different from the electron-proton collisions. These include the ion bunch preparation in the injector chain, acceleration and intrabeam scattering in the hadron ring, path length adjustment and synchronization with the electron ring, stochastic cooling upgrades, machine protection upgrades, and operation with polarized electron beams colliding with either unpolarized ion beams or polarized He-3.
JLab, Newport News, Virginia, USA
Stanford University, Stanford, California, USA
CalPoly, San Luis Obispo, California, USA
The Jefferson Lab Electron-Ion Collider (JLEIC) is an asymmetric high luminosity ring-ring collider proposed as the next major R&D facility for the nuclear physics community. Both of JLEIC’s electron and ion collider rings have high beam current with gaps serving the pur-poses of beam abort, ion clearing, etc. Such a time-varying beam loading in the RF cavities would generate modulation in cavity RF phase/voltage, causing cyclic shift of collision point and potential luminosity loss. We studied a few approaches to mitigate the RF phase modu-lation and IP shift, such as correcting the RF phase/voltage modulation with traditional LLRF feed-back, one-turn feedback (OTFB), or RF feedforward (FF); optimizing the bunch fill pattern to limit the RF phase/voltage modulation to a small fraction of the bunch trains in the collider ring; or matching the RF phase modulation in the two rings. The preliminary re-sults are discussed in this paper.
BNL, Upton, Long Island, New York, USA
LBNL, Berkeley, California, USA
BNL, Upton, Long Island, New York, USA
LBNL, Berkeley, California, USA
BNL, Upton, Long Island, New York, USA
The brand new non-magnetized bunched beam electron cooler (LEReC) [1] has been built to provide luminosity improvement for Beam Energy Scan II (BES-II) physics program at the Relativistic Heavy Ion Collider (RHIC) BES-II [2]. The LEReC accelerator includes a photocathode DC gun, a laser system, a photocathode delivery system, magnets, beam diagnostics, a SRF booster cavity, and a set of Normal Conducting RF cavities to provide sufficient flexibility to tune the beam in the longitudinal phase space. This high-current high-power accelerator was successfully commissioned in period of March -September 2018. Beam quality suitable for cooling has been demonstrated. In this paper we discuss beam commissioning results and experience learned during commissioning.
[1] A. Fedotov et al., ’Status of bunched beam electron cooler LEReC’ in these proceedings.
[2] C.Liu et al., ’Improving luminosity of Beam Energy Scan II at RHIC’ in these proceedings.
BNL, Upton, Long Island, New York, USA
FRIB, East Lansing, Michigan, USA
LBNL, Berkeley, California, USA
JLab, Newport News, Virginia, USA
The 2015 Nuclear Science Advisory Committee Long Rang Plan identified the need for an electron-ion collider (EIC) facility as a gluon microscope with capabilities beyond those of any existing accelerator complex. To reach the required high energy, high luminosity, and high polarization, the eRHIC design, based on the existing heavy ion and polarized proton collider RHIC, adopts a very small \beta-function at the interaction points, a high collision repetition rate, and a novel hadron cooling scheme. A full crossing angle of 22 mrad and crab cavities for both electron and proton rings are required. In this article, we will present the high priority R\&D items related to the beam-beam interaction studies for the current eRHIC design, the simulation challenges, and our plans and methods to address them. Recent progresses on this project are reported too.
BNL, Upton, Long Island, New York, USA
KEK, Ibaraki, Japan
LBNL, Berkeley, California, USA
In the eRHIC, to compensate the geometric luminosity loss, local crab cavities on both sides of the interaction points are to adopted. The previous strong-strong beam-beam simulations showed that the luminosity degradation depends on the crab cavity frequency, proton synchrotron tune, proton bunch length and so on. In this article, we apply a combined strong-strong and weak-strong beam-beam simulation to investigate the incoherent and coherent beam motions with crabbed collison, and to calculate more realistic beam emittance growth rates and luminosity degradation rate.
BNL, Upton, Long Island, New York, USA
Fermilab, Batavia, Illinois, USA
For the proposed electron-ion collider eRHIC, an electron storage ring will be installed in the existing RHIC tunnel. To reach the high luminosity of up to 1034 cm-2 sec-1, beam currents up to 2.5A have to be stored. Besides high luminosity the physics program requires spin polarization levels of 70 percent, with both spin "up" and spin "down" orientations present in the fill. This is only feasible by using a full-energy spin polarized injector that replaces bunches faster than the depolarization rate. To limit the repetition rate of that injector to about one hertz, the polarization lifetime in the storage ring has to be maximized by proper spin matching and countermeasures for the machine misalignments. We will give an overview of the electron storage ring design.
JLab, Newport News, Virginia, USA
The proposed Jefferson Lab Electron Ion Collider (JLE-IC) envisions an ion complex composed of an ion linac, two booster synchrotrons and a collider ring. The evolving design of the JLEIC booster required an increase in the extraction energy of the booster from 8 to 12.1 GeV kinetic energy, necessitating two machines instead of one. The decision was also made to switch to warm magnets, thus increasing the total radius of the 8 GeV booster. The second booster is now the same size as the collider rings. In this work we present the new designs for JLEIC’s Low Energy Booster (LEB) and High Energy Booster (HEB).
BNL, Upton, Long Island, New York, USA
The IR magnets for the eRHIC Collider proposed at BNL must provide strong fields for the high momentum hadron beam and yet protect the nearby electron beam focusing channel from these fields. In our initial design the electron and hadron magnets were staggered so their respective cold masses did not overlap; however, this restricts the longitudinal space for the first hadron quadrupole and led to the challenge of making a high-field Nb3Sn main coil structure fit inside limited radial space within an external field active shield coil. In our new layout the crossing angle increased from 22 to 25 mrad and the electron and hadron cold masses are now side-by-side. This layout allows longer magnetic lengths for reducing the coil peak fields; NbTi conductor can now be used everywhere. Of course we must take care to control magnetic cross talk between neighboring apertures. One trick we will use to accomplish this is to maximize the yoke material thickness between the beams by tapering (i.e. change coil radius as a function of longitudinal position) some of the electron coils. The new eRHIC IR layout and magnet design is reported in this paper along with ongoing R&D to wind tapered coils.
SLAC, Menlo Park, California, USA
The Microbunched Electron Cooling (MBEC) * is a promising cooling technique that can find applications in future hadron and electron-ion colliders. A 1D model of MBEC has been recently developed in Ref. **. This model predicts the cooling time below two hours for eRHIC 255 GeV proton beams, when two amplification sections are used in the cooling system. In this work, we go beyond the 1D model of Ref. * and develop a realistic 3D theory of MBEC. Our approach is based on the analysis of the dynamics of microscopic 3D fluctuations in the electron and hadron beams during their interaction and propagation through the system. We derive an analytical expression for the cooling rate and optimize it for the parameters of eRHIC. Our analytical results are in reasonable agreement with simulations.
* D. Ratner. Phys. Rev. Lett. 111, 084802 (2013).
** G. Stupakov. PRAB 21, 114402 (2018)
BNL, Upton, Long Island, New York, USA
The electron-ion collider eRHIC proposed by Brookhaven National Laboratory includes a crabbing system to reestablish head-on collisions for a maximum geometric overlap of the colliding bunches. Since the last cavity design, the crossing angle has increased from 22 to 25 mrad to relax the field strength requirement in one of the IR magnets - increasing the deflecting kick required to collider the bunches head on - and one of the considered options is to have both proton and electron crab cavities work at 200 MHz. The present paper discusses the RF design of the 200 MHz crab cavities for the electron and hadron beams of eRHIC.
ODU, Norfolk, Virginia, USA
JLab, Newport News, Virginia, USA
Electron cooling of the ion beam is key to obtaining the required high luminosity of proposed electron-ion colliders. For the Jefferson Lab Electron Ion Collider, the expected luminosity of 1034 〖 cm〗-2 s-1 will be achieved through so-called ’magnetized electron cooling’, where the cooling process occurs inside a solenoid field, which will be part of the collider ring and facilitated using a circulator ring and Energy Recovery Linac (ERL). As an initial step, we generated magnetized electron beam using a new compact DC high voltage photogun biased at -300 kV employing an alkali-antimonide photocathode. This contribution presents the characterization of the magnetized electron beam (emittance variations with the magnetic field strength for different laser spot sizes) and a comparison to GPT simulations.
JLab, Newport News, Virginia, USA
The recent National Academies of Science Review concluded the science questions that could be answered by an electron-ion collider are significant to advancing our understanding of the atomic nuclei that make up all visible matter in the universe. To meet this science need, a high luminosity polarized electron-ion collider (JLEIC) was envisioned at Jefferson Lab, based on the existing CEBAF recirculated SRF electron linac. Over the past 16 years, Jefferson Lab has been actively engaged in the design study and accelerator R&D for JLEIC, a comprehensive Pre-Conceptual Design Report has been completed recently. The JLEIC baseline design has also been continuously optimized including extending the CM energy to 100 GeV. In this paper, we present a summary of the JLEIC baseline design and also briefly discuss the accelerator R&D.
SLAC, Menlo Park, California, USA
JLab, Newport News, Virginia, USA
Design of the Jefferson Lab Electron-Ion Collider (JLEIC) includes low-beta Interaction Region (IR) and spin rotator optics for high luminosity and polarization. Magnet errors, especially in the high-beta final focus quadrupoles, result in optics perturbations which need to be corrected in order to attain sufficient dynamic aperture (DA). We present design of orbit correction system for the electron ring and evaluate its performance. The DA is then studied including misalignment, magnet strength errors, non-linear field errors, and corrections.
IHEP, Beijing, People’s Republic of China
JLab, Newport News, Virginia, USA
SLAC, Menlo Park, California, USA
The design concept of electron collider ring in the Jefferson Lab Electron-Ion Collider (JLEIC) is based on a small beam size at the interaction point (IP) to boost the luminosity. With a chosen beta-star at the IP, electron beam size is determined by the equilibrium emittance obtained from the linear optics design. In this paper, we present an update on the lattice design of the electron ring considering not only preservation of low beam emittance, but also optimization of geometric arrangement. In particular, recent development of the lattice design has been focused on incorporating the vertical dogleg, which brings the electron beam to the ion beam plane for collisions, in the spin rotator design. The vertical dogleg is designed with no horizontal emittance growth, controlled vertical emittance and no first-order effect on the electron polarization.
JLab, Newport News, Virginia, USA
BNL, Upton, Long Island, New York, USA
MIPT, Dolgoprudniy, Moscow Region, Russia
ODU, Norfolk, Virginia, USA
Science and Technique Laboratory Zaryad, Novosibirsk, Russia
High electron and ion polarizations are some of the key design requirements of a future Electron Ion Collider (EIC). The transparent spin mode, a concept inspired by the figure 8 ring design of JLEIC, is a novel technique for preservation and control of electron and ion spin polarizations in a collider or storage ring. It makes the ring lattice "invisible" to the spin and allows for polarization control by small quasi-static magnetic fields with practically no effect on the beam’s orbital characteristics. It offers unique opportunities for polarization maintenance and control in Jefferson Lab’s JLEIC and in BNL’s eRHIC. The transparent spin mode has been demonstrated in simulations and we now plan to test it experimentally. We present a design of an experiment using a polarized proton beam stored in one of the RHIC rings. In the experiment, one of the RHIC rings is configured in the transparent spin mode by aligning the axes of its two Siberian snakes. The experiment goals, procedures, hardware requirements and expected results are presented.
JLab, Newport News, Virginia, USA
SLAC, Menlo Park, California, USA
LBNL, Berkeley, California, USA
Nuclear physics experiments envisioned at a proposed future Electron-Ion Collider (EIC) require high luminosity of 1033-1034 cm-2s-1 and a full-acceptance detector capable of reconstruction of a whole electron-ion collision event. Due to a large asymmetry in the electron and ion momenta in an EIC, the particles associated with the initial ion tend to go at very small angles and have small rigidity offsets with respect to the initial ion beam. They are detected after they pass through the apertures of the final focusing quadrupoles. Therefore, the apertures must be sufficiently large to provide the acceptance required by experiments. In addition, to maximize the luminosity, the final focusing quadrupoles must be placed as close to the interaction point as possible. A combination of these requirements presents serious detection, optics and engineering design challenges. We present a design of a full-acceptance interaction region of Jefferson Lab Electron-Ion Collider (JLEIC). The paper presents how this design addresses the above requirements up to an ion momentum of 200 GeV/c. We summarize the magnet parameters, which are kept consistent with the Nb-Ti superconducting magnet technology.
JLab, Newport News, Virginia, USA
BNL, Upton, Long Island, New York, USA
MIPT, Dolgoprudniy, Moscow Region, Russia
ODU, Norfolk, Virginia, USA
Science and Technique Laboratory Zaryad, Novosibirsk, Russia
In the Spin Transparency (ST) mode of RHIC, the axes of its Siberian snakes are parallel. The spin tune in the ST mode is zero and the spin motion becomes degenerate: any spin direction repeats every particle turn. In contrast, the lattice of a conventional collider determines a unique stable periodic spin direction, so that the collider operates in the Preferred Spin (PS) mode. Contributions of perturbing magnetic fields to the spin resonance strengths in the PS mode are usually calculated using the spin response function. However, in that form, it is not applicable in the ST mode. This paper presents a response function formalism expanded for the ST mode of operation of conventional colliders with two identical Siberian snakes in the highly-relativistic limit. We present calculations of the spin response function for RHIC in the ST mode.