BNL, Upton, Long Island, New York
Dual partial snake scheme has provided polarized proton beams with 1.5*1011 intensity and 65% polarization for RHIC spin program. To overcome the residual polarization loss due to horizontal resonances in the AGS, a new string of quadrupoles have been added. The horizontal tune can now be set in the spin tune gap generated by the two partial snakes, such that horizontal resonances are avoided. This paper presents the accelerator setup and preliminary results.
BNL, Upton, Long Island, New York
ALBA, Bellaterra (Cerdanyola del Valles)
Since 2001 RHIC has experienced electron cloud effects, which have limited the beam intensity. These include dynamic pressure rises – including pressure instabilities, a reduction of the stability threshold for bunches crossing the transition energy, and possibly slow emittance growth. We report on the main observations in operation and dedicated experiments, as well as the effect of various countermeasures including baking, NEG coated warm pipes, pre-pumped cold pipes, bunch patterns, scrubbing, and anti-grazing rings.
BNL, Upton, Long Island, New York
Snake depolarizing resonances due to the imperfect cancellation of the accumulated perturbations on the spin precession between snakes were observed at the Relativistic Heavy Ion Collider~(RHIC). During the RHIC 2005 and 2006 polarized proton runs, we mapped out the spectrum of odd order snake resonance at Qy=7/10. Here, Qy is the beam vertical betatron tune. We also studied the beam polarization after crossing the 7/10th resonance as a function of resonance crossing rate. This paper reports the measured resonance spectrum as well as the results of resonance crossing.
The work was performed under the US Department of Energy Contract No. DE-AC02-98CH1-886, and with support of RIKEN(Japan) and RenaissanceTechnologies C orp.(USA)
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.
BNL, Upton, Long Island, New York
Gold ions for the 2007 run of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) are accelerated in the Tandem, Booster and AGS prior to injection into RHIC. The setup and performance of this chain of accelerators will be reviewed with a focus on improvements in the quality of beam delivered to RHIC. In particular, more uniform stripping foils between Booster and AGS, and a new bunch merging scheme in AGS promise to provide beam bunches with reduced longitudinal emittance for RHIC.
IUCF, Bloomington, Indiana
BNL, Upton, Long Island, New York
Two partial helical dipole snakes were found to be able to overcome all imperfection and intrinsic spin resonances provided that the vertical betatron tunes were maintained in the spin tune gap near the integer 9. Recent vertical betatron tune scan showed that the two weak resonances at the beginning of the acceleration cycle may be the cause of polarization loss. This result has been confirmed by the vertical polarization profile measurement, and spin tracking simulations. Possible cure of the remaining beam polarization is discussed.
BNL, Upton, Long Island, New York
The AGS synchrotron employs two partial helical snakes* to preserve the polarization of the proton beam during acceleration in the AGS. The effect of the helical snakes on the beam optics is significant at injection energy, with the effect greatly diminishing early in the acceleration cycle. In order to compensate for the effect of the snakes on the beam optics, we have introduced eight compensation quadrupoles in straight sections of the AGS at the proximity of the partial snakes. At injection the strength of these eight quads is set at a high value but ramped down to zero when the effect of the snakes diminishes. Four of the compensation quadrupoles had to be placed in very short straight sections therefore had to be 'thin' with a length of ~30 cm. The 'thin' quadrupoles were laminated and designed to minimize the strength of the dodecoupole harmonic. The thickness of the lamination was also calculated** to keep the ohmic losses generated by the eddy currents in the laminations below an acceptable limit. Comparison of the measured and calculated harmonics will be presented and the ohmic losses due to the eddy currents, as a function of time during rumping will be discussed.
* H. Huang, et al., Proc. EPAC06, (2006), p. 273.** OPERA computer code. Vector Fields Inc.
BNL, Upton, Long Island, New York
ITEP, Moscow
UW-Madison/PD, Madison, Wisconsin
Yale University, Physics Department, New Haven, CT
UCR, Riverside, California
RBRC, Upton, Long Island, New York
Kyoto University, Kyoto
IUCF, Bloomington, Indiana
The spin physics program at the Relativistic Heavy Ion Collider (RHIC) requires knowledge of the proton beam polarization to better than 5%. To achieve this goal, a polarized hydrogen jet target was installed in RHIC where it intersects both beams. The premise is to utilize the precise knowledge of the jet proton polarization to measure the analyzing power in the proton - proton elastic scattering process in the Coulomb Nuclear Interference (CNI) region at the prescribed RHIC proton beam energy, then use the reverse reaction to measure the degree of the beam polarization, and finally confront the results with simultaneous measurements by the fast high statistics polarimeter that measure the p-Carbon elastic scattering process in the CNI region to calibrate the latter. In this presentation, the polarized jet target mechanics, operation, detector systems and the p-Carbon polarimeter are described. The statistical accuracy attained as well as the systematic uncertainties will be discussed. Such techniques may well become the standard for high energy polarized proton beams planned elsewhere in Russia and Japan.