BNL, Upton, Long Island, New York
MIT, Middleton, Massachusetts
A new high-brightness synchrotron light source (NSLS-II) is under design at BNL. The 3-GeV NSLS-II storage ring has a double-bend achromatic lattice with damping wigglers installed in zero-dispersion straights to reduce the emittance below 1nm. In this note, we present an overview of the impact of collective effects upon the performance of the storage ring. Subjects discussed include Touschek lifetime, intra-beam scattering, instability thresholds due to ring impedance, and use of a third-harmonic Landau cavity.
BNL, Upton, Long Island, New York
Beam-beam effects present one of major factors limiting the luminosity of colliders. In the linac-ring option of eRHIC design, an electron beam accelerated in a superconducting energy recovery linac collides with a proton beam circulating in the RHIC ring. There are some features of beam-beam effects which require careful examination in linac-ring configuration. First, the beam-beam interaction can induce specific head-tail type instability of the proton beam referred to as kink instability. Thus, beam stability conditions should be established to avoid proton beam loss. Also, the electron beam transverse disruption by collisions has to be evaluated to ensure beam quality is good enough for the energy recovery pass. In addition, fluctuations of electron beam current and/or electron beam size, as well as transverse offset, can cause proton beam emittance growth. The tolerances for those factors should be determined and possible countermeasures should be developed to mitigate the emittance growth. In this paper, a soft Gaussian strong-strong simulation is used to study all of mentioned beam-beam interaction features and possible techniques to reduce the emittance growth.
BNL, Upton, Long Island, New York
To achieve the RHIC polarized proton enhanced luminosity goal of 150*1030 cm-2 sec-1 on average in stores at 250 GeV, the luminosity needs to be increased by a factor of 3 compared to what was achieved in 2006. Since the number of bunches is already at its maximum of 111, limited by the injection kickers and the experiments' time resolution, the luminosity can only be increased by either increasing the bunch intensity and/or reducing the beam emittance. This leads to a larger beam-beam tuneshift parameter. Operation during 2006 has shown that the beam-beam interaction is already dominating the luminosity lifetime. To overcome this limitation, a near-integer working point is under study. We will present recent results of these studies.
BNL, Upton, Long Island, New York
After the last successful RHIC Au-Au run in 2004 (Run-4), RHIC experiments now require significantly enhanced luminosity to study very rare events in heavy ion collisions. RHIC has demonstrated its capability to operate routinely above its design average luminosity per store of 2x1026 cm-2 s-1. In Run-4 we already achieved 2.5 times the design luminosity in RHIC. This luminosity was achieved with only 40% of bunches filled, and with β* = 1 m. However, the goal is to reach 4 times the design luminosity, 8x1026 cm-2 s-1, by reducing the beta* value and increasing the number of bunches to the accelerator maximum of 111. In addition, the average time in store should be increased by a factor of 1.1 to about 60% of calendar time. We present an overview of the changes that increased the instantaneous luminosity and luminosity lifetime, raised the reliability, and improved the operational efficiency of RHIC Au-Au operations during Run-7.
BNL, Upton, Long Island, New York
ITEP, Moscow
The Relativistic Heavy Ion Collider~(RHIC) as the first high energy polarized proton collider was designed to provide polarized proton collisions at a maximum beam energy of 250GeV. It has been providing collisions at a beam energy of 100GeV since 2001. Equipped with two full Siberian snakes in each ring, polarization is preserved during the acceleration from injection to 100GeV with careful control of the betatron tunes and the vertical orbit distortions. However, the intrinsic spin resonances beyond 100GeV are about a factor of two stronger than those below 100GeV making it important to examine the impact of these strong intrinsic spin resonances on polarization survival and the tolerance for vertical orbit distortions. Polarized protons were accelerated to the record energy of 250GeV in RHIC with a polarization of 45\% measured at top energy in 2006. The polarization measurement as a function of beam energy also shows some polarization loss around 136GeV, the first strong intrinsic resonance above 100GeV. This paper presents the results and discusses the sensitivity of the polarization survival to orbit distortions.
Jefferson Lab, Newport News, Virginia
IUCF, Bloomington, Indiana
BTG, New York
BNL, Upton, Long Island, New York
ANL, Argonne, Illinois
Experiments on the study of fundamental quark-gluon structure of nucleons require an electron-light ion collider of a center of mass energy from 20 to 65 GeV at luminosity level of 1035 cm-2s-1 with both beams polarized. A CEBAF accelerator based ring-ring collider of 7 GeV electrons/positrons and 150 GeV light ions is envisioned as a possible next step after the 12 GeV CEBAF Upgrade. The developed ring-ring scheme takes advantage of the existing polarized continuous electron beam and SRF linac, the green-field design of the collider rings and the ion accelerator complex with electron cooling. We report results of our design studies of the ring-ring version of an electron-light ion collider of the required luminosity.
BNL, Upton, Long Island, New York
Polarized protons are injected into the Relativistic Heavy Ion Collider (RHIC) just above transition energy. When installation of a cold partial Siberian snake in the AGS required lowering the injection energy by Delta gamma=0.56, the transition energy in RHIC had to be lowered accordingly to ensure proper longitudinal matching. This paper presents lattice modifications implemented to lower the transition energy by ∆ γt=0.8.
BNL, Upton, Long Island, New York
To further improve the the polarized proton (pp) luminosity in the Relativistic Heavy Ion Collider, the beta functions at the two interaction points (IPs) will be reduced from 1.0 m to 0.9m in 2007. In addition, it is planned to increase the bunch intensity from 1.5*1011 to 2.0*1011. To accommodate these changes, the nonlinear chromaticities and the third resonance driving term should be corrected. In 2007, the number of the arc sextupole power supplies will be doubled from 12 to 24, which allows nonlinear chromaticity correction. With the updated field errors in the interaction regions (IRs), detailed dynamic aperture studies are carried out to optimize the nonlinear correction schemes, and increase the available tune space in collision.
BNL, Upton, Long Island, New York
The beam lifetime in most medium-energy synchrotron radiation sources is limited by the Touschek effect, which describes the momentum transfer from the transverse into the longitudinal direction due to binary collisions between electrons. While an analytical formula exists to calculate the resulting lifetime, the actual momentum acceptance necessary to perform this calculation can only be determined by tracking. This is especially the case in the presence of small vertical apertures at insertion devices. In this case, nonlinear betatron coupling leads to beam losses at these vertical aperture restrictions. In addition, a realistic model of the storage ring is necessary for calculation of the equilibrium beam sizes (particularly in the vertical direction) which are important for a self-consistent lifetime calculation.