BNL, Upton, Long Island, New York, USA
Providing Au-Au collisions in the Relativistic Heavy Ion Collider (RHIC) at energies equal or lower than 10 GeV/nucleon is of particular interest to study the location of a critical point in the QCD phase diagram. To mitigate luminosity limitations arising from intra-beam scattering at such low energies, an electron cooling system is being developed. To achieve cooling, the relative velocities of the electrons and protons need to be small with maximized transverse overlap. Recombination rates of ions with electrons in the electron cooler can provide signals that can be used to tune the energies and transverse overlap to the required conditions. In this paper we take a close look at various detection methods for recombination processes that may be used to approach cooling.
BNL, Upton, Long Island, New York, USA
ESRF, Grenoble, France
Collisions with beams of highly asymmetric rigidities (proton-Gold and proton-Aluminum) were provided for the RHIC physics programs in 2015. Magnets were moved for the first time in RHIC prior to the run to accommodate the asymmetric beam trajectories during acceleration and at store. A special ramping scheme was designed to keep the revolution frequencies of the beams in the two rings equal. The unique operational experience of the asymmetric run will be reviewed.
BNL, Upton, Long Island, New York, USA
FZJ, Jülich, Germany
ESRF, Grenoble, France
The Relativistic Heavy Ion Collider (RHIC) has two main operating modes with heavy ions and polarized protons respectively. In addition to a continuous increase in the bunch intensity in all modes, two major new systems were completed recently mitigating the main luminosity limit and leading to significant performance improvements. For heavy ion operation stochastic cooling mitigates the effects of intrabeam scattering, and for polarized proton operation head-on beam-beam compensation mitigated the beam-beam effect. We present the performance increases with these upgrades for heavy ions and polarized protons, as well as an overview of all operating modes past and planned.
BNL, Upton, Long Island, New York, USA
An internal halo target has been installed in the STAR detector at RHIC to extend the energy range towards lower energies and increase the event rates in the search for the critical point in the QCD phase diagram. We discuss geometric considerations that led to the present target layout and present first operational results.
BNL, Upton, Long Island, New York, USA
Lower risk ring-ring alternatives to the BNL linac-ling~[linacring] eRHIC electron ion collider (EIC) are discussed. The baseline from the Ring-Ring Working Group~[ringring] has a peak proton-electron luminosity of ≈§I{1.2e33}{cm-2.s-1}. An option has final focus quadrupoles starting immediately after the detector at 4.5~m, instead of at 32~m in the baseline. This allows the use of lower β*s. It also uses more, 720, lower intensity, bunches, giving reduced IBS emittance growth and requiring only low energy pre-cooling. It has a peak luminosity of ≈§I{7e33}{cm-2.s-1}. An upgrade of this option, requiring magnetic, or coherent, electron cooling, has 1440 bunches and peak luminosity of ≈§I{15e33}{cm-2.s-1}.
BNL, Upton, Long Island, New York, USA
The 15mrad beam crossing angle in the eRHIC ring-ring interaction region requires crab crossing of the 250GeV proton beam to restore the luminosity. Since the product of the RF voltage and the RF frequency of the crab cavities is constant for a given crossing angle, higher frequencies are preferred in order to limit the require voltage. However, the 20cm RMS proton bunch length provides an upper limit of the useable frequencies due to the significant curvature of the RF waveform over this bunch length. To study the effectof realistic crab cavities with a finite wavelength on electron beam-beamdynamics and to determine the potential need for higher harmonic crab cavities to linearize the kick a simulation code has been developed.
BNL, Upton, Long Island, New York, USA
To reduce the technical risk of the future electron-ion collider eRHIC currently under study at BNL, the ring-ring scheme has been revisited over the summer of 2015. The goal of this study was a design that covers the full center-of-mass energy range from 32 to 141 GeV with an initial luminosity around 1033 cm-2 sec-1, upgradeable to 1034 cm-2 sec-1 later on. In this presentation the baseline design will be presented, and future upgrades will be discussed.
BNL, Upton, Long Island, New York, USA
The 2015 ring-ring design study of the electron-ion collider eRHIC aims at an e-p luminosity around 1033 cm-2 sec-1 over a center-of-mass energy range from 32 to 141 GeV, while at the same time providing the required detector geometry and acceptance for the proposed physics program. The latest interaction region design will be presented.
BNL, Upton, Long Island, New York, USA
High electron beam polarization (70-80%) is required in the future electron-ion collider eRHIC over the whole electron beam energy range from 5 GeV to 20 GeV. This paper analyzes important aspects for achieving a high electron polarization level in the ring-ring design option of eRHIC and presents the design of spin rotators required to generate the longitudinal polarization orientation at the interaction point. Experiment considerations require bunch spin patterns with both spins up and down. A highly polarized beam will be produced by a photo-injector, accelerated to full collision energy by an injector accelerator and injected into the storage ring. Beam depolarization time in the storage ring has to be minimized in the presence of spin rotators, detector solenoid and damping wiggler, which establishes specific requirements for the ring lattice.
BNL, Upton, Long Island, New York, USA
During the FY 2013 RHIC polarized proton run, deterioration of the abort kicker system was observed. The reduced kicks resulted in quenching the superconducting quadrupole Q4 downstream of the beam dump. Frequent re-tuning of the modulator wave form temporarily mitigated the effect, which worsened during the course of the run. Beam-induced heating of the kicker ferrites was evenutally identified as the root cause of this behavior. We report our observations and discuss modifications to the kickers.