Improvements of NSLS-II X-ray Diagnostic Beamlines
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43 PARTICLE ACCELERATORS↗
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Results for “eRHIC”
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Niobium-coated copper cavities for the eRHIC crabbing system
Crabbing of hadron bunches in particle colliders requires high kick voltages in the order of MV. The crabbing system of the High Luminosity Large Hadron Collider (HL-LHC) will be using Double-Quarter Wave (DQW) and Radio-Frequency Dipole (RFD) cavities, both compact deflecting cavity designs fabricated from bulk Nb sheets. In the same fashion, the baseline crabbing system for the electron Relativistic Heavy Ion Collider (eRHIC) will consist of a series of DQWcavities. Encouraging cryogenic RF performances of a Nb/Cu Quarter-Wave Resonator (QWR) and the proposal of a niobium-coated copper (Nb/Cu) Wide- OpenedWaveguide (WOW) cavity for deflecting purposes stimulated the necessity to review the possibilities of Nb/Cu cavities for the future crabbing system of eRHIC. This note will study the feasibility of usingWOW cavities for the eRHIC crabbing system and will compare the expected performances of DQW and WOW cavities based on the latest cryogenic RF results.
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An Improved eRHIC Interaction Region Design without High Field Nb3sn Magnets
The Electron-Ion Collider (EIC) is envisioned as the next DOE Nuclear Physics facility. BNL 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-2sec-1. An electron storage ring with an energy range from 5 to 18 GeV will be added in the existing RHIC tunnel. The beams will collide in up to two Interaction Regions (IRs). Balancing conflicting experimental physics and machine accelerator physics demands with realistic eRHIC IR magnet designs requires new concepts and careful attention to detail. We review recent work aimed at reducing IR magnet cost and at avoiding risk associated with using a high-field Nb3Sn actively shielded quadrupole that was present in an earlier design.
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eRHIC Beam Scrubbing
We propose using beam scrubbing to mitigate the electron cloud effect in the eRHIC. The bunch number is adjusted below the heat load limit, then it increases with the reduced secondary electron yield resulted from the beam scrubbing, up to the design bunch number. Since the electron density threshold of beam instability is lower at the injection, a preliminary injection scrubbing should go first, where large chromaticity can be used to keep the beam in the ring for scrubbing. After that, the beam can be ramped to full energy, allowing physics scrubbing. Simulations demonstrated that with beam scrubbing in a reasonable period of time, the eRHIC baseline design is feasible.
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Proton Beam Emittance Growth due to Centroid Fluctuations in Strongly Disrupted Electron Bunches in the Linac-Ring eRHIC
In the energy recovery linac (ERL) based eRHIC design, the electron beam, accelerated in a superconducting ERL, collides with the proton beam circulating in the RHIC ring ones, undergoing a very strong beam-beam interaction with the protons, which warrants careful examination. Following the analysis of the transverse disruption and linear mismatch effects in the electron beam caused by beam-beam collision discussed in [2], we adopt the beam parameters listed in Table I for the eRHIC linac-ring design. After a review of the electron disruption process, we perform long term strong-strong beam-beam simulations with a modification of K. Ohmi’s strong-strong beam-beam code BBSS, with the modification consisting of the regeneration of the electron beam after every collision with the proton beam. With the parameters listed in Table I, a kink instability is observed in the proton beam. By reducing the proton bunch length, thus decreasing the electron disruption parameter, the kink instability is observed to disappear for a proton bunch length σ z,p < 10 cm, or electron disruption parameter d e < 1.5. The effect of random offsets in the electron bunch centroids on the long term stability of the proton beam is studied next, with a proton bunch length σ z,p = 6.3 cm (d e = 0.9), thus below the kink instability threshold. The random offsets of the electron bunch centroids are assumed to be Gaussian distributed, with standard deviation offs, and "delta-correlated" in time (white noise). Studies to take into account finite time-correlation effects and random offsets generated by non-Gaussian random processes will be considered in the future. The effect from fluctuations in the electron bunch population has been studied analytically and will be discussed numerically in a companion paper.
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Design of a tapered final focusing magnet for eRHIC
Presently the electron-ion collider eRHIC is underdesign, which aims to provide a facility with a peak luminosity of 10 34 cm –2 sec –1 . Particularly challenging in terms of magnet design are the IR magnets due to the close proximity of the electron and hadron beams. This paper outlines the design for the so-called Q1 rear side magnet, which is a double aperture quadrupole magnet 7.2 m from the interaction region. Due to space restrictions both magnets are housed in the same iron yoke. The aperture of the hadron quadrupole is relatively small, but requires high gradients. While the required gradient for the electron quadrupole is relatively small, the aperture of this magnet needs to accommodate the beam and allow the synchrotron radiation fan to pass through. To accomplish this both quadrupole magnets have a tapered aperture. Furthermore to keep the gradients constant along the length of the magnets a special winding pattern has been identified, which is described in this paper.
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The eRHIC spin rotator and the beam optics of the 400 MeV transfer line to RCS
The 400 MeV LINAC 1 of the proposed eRHIC collider 1 is the first acceleration stage of the 18 GeV electron accelerator. The second acceleration stage of the electron accelerator is the Rapid Cycling Synchrotron (RCS), which can increase the energy of the electron bunches to 18 GeV and subsequently extract transfer and inject the 18 GeV electron bunches into the 18 GeV electron Storage Ring (SR) to collide with the hadron bunches of the existing (Relativistic Heavy Ion Collider (RHIC)) accelerator. This paper describes the beam optics of the transfer line between the 400 MeV LINAC and the RCS accelerator (LtRCS). The function of the LtRCS line is twofold, first to transfer the electron beam from the exit of the 400 MeV LINAC to the injection point of the RCS 1 and second to rotate the stable spin direction of the polarized electrons from the longitudinal direction to the vertical. A detailed description of the constraints to be satisfied by the LtRCS transfer line will be given. Finally, a section will also be devoted to discuss the spin rotator 2 .
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eRHIC Design Status
The electron-ion collider eRHIC aims at a luminosity around 10³⁴cm⁻²sec⁻¹, using strong cooling of the hadron beam. Since the required cooling techniques are not yet readily available, an initial version with a peak luminosity of 3*10³³cm⁻²sec⁻¹ is being developed that can later be outfitted with strong hadron cooling. We will report on the current design status and the envisioned path towards 10³⁴cm⁻²sec⁻¹ luminosity.
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eRHIC Electron Ring Design Status
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.
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eRHIC Design Overview
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.
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eRHIC Design Update
The future electron-ion collider (EIC) aims at an electron-proton luminosity of 10³³ to 10³⁴ cm⁻² sec⁻¹ and a center-of-mass energy range from 20 to 140 GeV. 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.
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On the effects of detector solenoids on n → 0 in RHIC and eRHIC
Two effects, in RHIC, from STAR solenoid and from a model of sPHENIX detector solenoid, are reviewed based on tracking simulations: a change in the stable spin precession direction n → 0 around the ring, and coupling. The method can be applied, mutatis mutandis , to eSTAR, sPHENIX and BeAST detector solenoids in A- and e-eRHIC.
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An ergodic approach to polarization in eRHIC electron storage ring
Electron polarization in a storage ring is subject to two long term effects: Sokolov-Ternov polarization and depolarization by diffusion, which over a long time scale lead to an equilibrium state. Simulation-wise, this can be highly CPU time and memory consuming. Simulations aimed at determining optimal ring storage energy in an electron-ion collider use to track thousand particle bunches, for a long time - yet still short compared to depolarization time scales, due to HPC limitations. Based on considerations of ergodicity of electron bunch dynamics in the presence of synchrotron radiation, tracking a single particle instead is investigated. This allows substantial saving in teh required HPC volume, “CPU-time×Memory-allocation”. The concept is illustrated with polarization lifetime and equilibrium polarization simulations at the eRHIC electron-ion collider.
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Spin simulations in eRHIC Wien filter
This Technical Note introduces to a simulation of spin dynamics in a Wien filter used as a spin rotator, based on (i) the use of a semi-analytical model for the electrostatic and magnetostatic vectors and (ii) step-wise ray-tracing techniques. It shows that the method reproduces theoretical expectations.
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Polarization Studies for the eRHIC Electron Storage Ring
A hadron/lepton collider with polarized beams has been under consideration by the scientific community since some years, in the U.S. and Europe. Among the various proposals, those by JLAB and BNL with polarized electron and proton beams are currently under closer study in the U.S. In the BNL Ring-Ring design electrons are stored at top energy in a ring to be accommodated in the existing RHIC tunnel. The transversely polarized electron beam is injected into the storage ring at variable top energy, between 5 and 18 GeV. Polarization is brought into the longitudinal direction at the IP by a couple of spin rotators. In addition experimenters call for the simultaneous storage of electron bunches with both spin helicities. In this paper studies of the attainable beam polarization level and lifetime in the storage ring at 18 GeV are presented.
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eRHIC - an Electron-Ion Collider at BNL
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