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| MOAA004 | RHIC Operational Status | 358 |
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Funding: Work was performed under the auspices of the U.S. Department of Energy. As the first hadron accelerator and collider consisting of two independent superconducting rings RHIC has operated with a wide range of beam energies and particle species. Machine operation and performance will be reviewed that includes high luminosity gold-on-gold and copper-on-copper collisions at design beam energy (100 GeV/u), asymmetric deuteron-on-gold collisions as well as high energy polarized proton-proton collisions (100 GeV on 100 GeV). Plans for future upgrades of RHIC will also be discussed. |
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| MOPA009 | Global Decoupling on the RHIC Ramp | 659 |
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Funding: Work supported by U.S. DOE under contract No. DE-AC02-98CH10886. The global betatron decoupling on the ramp is an important issue for the operation of the Relativistic Heavy Ion Collider (RHIC). In the polarized proton run, the betatron tunes are required to keep almost constant on the ramp to avoid spin resonance line crossing and the beam polarization loss. Some possible correction schemes on the ramp, like three-ramp correction, the coupling amplitude modulation and the coupling phase modulaxtion, have been found. The principles of these schemes are shortly reviewed and compared. Operational results of their applications on the RHIC ramps are given. |
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| MOPA007 | Polarized Proton Collisions at RHIC | 600 |
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Funding: The work was performed under the auspices of the U.S. Department of Energy and RIKEN Japan. The Relativistic Heavy Ion Collider~(RHIC) provides not only collisions of ions but also collisions of polarized protons. In a circular accelerator, the polarization of polarized proton beam can be partially or fully lost when a spin depolarizing resonance is encountered. To preserve the beam polarization during acceleration, two full Siberian snakes were employed in RHIC to avoid depolarizing resonances. In 2003, polarized proton beams were accelerated to 100~GeV and collided in RHIC. Beams were brought into collisions with longitudinal polarization at the experiments STAR and PHENIX by using spin rotators. RHIC polarized proton run experience demonstrates that optimizing polarization transmission efficiency and improving luminosity performance are significant challenges. Currently, the luminosity lifetime in RHIC is limited by the beam-beam effect. The current state of RHIC polarized proton program, including its dedicated physics run in 2005 and efforts to optimize luminosity production in beam-beam limited conditions are reported. |
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| MPPT046 | Superconducting Helical Snake Magnet for the AGS | 2935 |
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Funding: DOE A superconducting helical magnet has been built for polarized proton acceleration in the Brookhaven AGS. This "partial Snake" magnet will help to reduce the loss of polarization of the beam due to machine resonances. It is a 3 T magnet some 1940 mm in magnetic length in which the dipole field rotates with a pitch of 0.2053 degrees/mm for 1154 mm in the center and a pitch of 0.3920 degrees/mm for 393 mm in each end. The coil cross-section is made of two slotted cylinders containing superconductor. In order to minimize residual offsets and deflections of the beam on its orbit through the Snake, a careful balancing of the coil parameters was necessary. In addition to the main helical coils, a solenoid winding was built on the cold bore tube inside the main coils to compensate for the axial component of the field that is experienced by the beam when it is off-axis in this helical magnet. Also, two dipole corrector magnets were placed on the same tube with the solenoid. A low heat leak cryostat was built so that the magnet can operate in the AGS cooled by several cryocoolers. The design, construction and performance of this unique magnet will be summarized. |
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| TPAP044 | Observations of Snake Resonance in RHIC | 2839 |
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Funding: The work was performed under the auspices of the U.S. Department of Energy. Siberian snakes now become essential in the polarized proton acceleration. With proper configuration of Siberian snakes, the spin precession tune of the beam becomes $\frac{1}{2}$ which avoids all the spin depolarizing resonance. However, the enhancement of the perturbations on the spin motion can still occur when the betatron tune is near some low order fractional numbers, called snake resonances, and the beam can be depolarized when passing through the resonance. The snake resonances have been confirmed in the spin tracking calculations, and observed in RHIC with polarized proton beam. Equipped with two full Siberian snakes in each ring, RHIC provides us a perfect facility for snake resonance studies. This paper presents latest experimental results. New insights are also discussed. |
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| TPAP051 | Principle of Global Decoupling with Coupling Angle Modulation | 3132 |
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Funding: Work supported by U.S. DOE under contract No. DE-AC02-98CH10886. The global betatron decoupling on the ramp is an important issue for the operation of the Relativistic Heavy Ion Collider (RHIC). A new scheme coupling phase modulation is found. It introduces a rotating extra coupling into the coupled machine to detect the residual coupling. The eigentune responses are measured with a high resolution phase lock loop (PLL) system. From the minimum and maximum tune splits, the correction strengths are given. The time period occupied by one coupling phase modulation is less than 10 seconds. So it is a very promising solution for the global decoupling on the ramp. In this article the principle of the coupling phase modulation is given. The simulation with the smooth accelerator model is also done. The practical issues concerning its applications are discussed. |
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| TPAP052 | Possible Phase Loop for the Global Decoupling | 3182 |
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Funding: Work supported by U.S. DOE under contract No. DE-AC02-98CH10886. Besides two eigentunes Q1 and Q2 , two amplitude ratios r1 and r2 and two phase differences ∆ φ1 and ∆ φ2 are introduced for the global coupling observation. Simulations are carried out to check their behaviors in the process of the skew quadrupole strength scans. Some attractive features of the phase differences ∆ φ1,2 have been found, which are possibly useful for the global decoupling phase loop, or future global decoupling feedback. Analytical descriptions to these 6 quantities are described in the Twiss parameters through the linear coupling's action-angle parameterization, or in coupling coefficient through the linear coupling's Hamiltonian perturbation theory. Dedicated beam experiments are carried out at the Relativistic Heavy Ion Collider (RHIC) to check the global coupling observables from the phase lock loop (PLL) system. The six observables are measured under PLL driving oscillations during the 1-D and 2-D skew quadrupole scans. The experimental results are reported and discussions are given. |
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| TPAP055 | Fast IR orbit feedback at RHIC | 3298 |
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Funding: Work performed under the auspices of the US Department of Energy Mechanical low-beta triplet vibrations lead to horizontal jitter of RHIC beams at frequencies around 10 Hz. The resulting beam offsets at the interaction points are considered detrimental to RHIC luminosity performance. To stabilize beam orbits at the interaction points, installation of a fast orbit feedback is foreseen. A prototype of this system is being developed and tested. Recent results are presented. |
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| TPAP043 | Electron Cooling of RHIC | 2741 |
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We report progress on the R&D program for electron-cooling of the Relativistic Heavy Ion Collider (RHIC). This electron cooler is designed to cool 100 GeV/nucleon at storage energy using 54 MeV electrons. The electron source will be a superconducting RF photocathode gun. The accelerator will be a superconducting energy recovery linac. The frequency of the accelerator is set at 703.75 MHz. The maximum electron bunch frequency is 9.38 MHz, with bunch charge of 20 nC. The R&D program has the following components: The photoinjector and its photocathode, the superconducting linac cavity, start-to-end beam dynamics with magnetized electrons, electron cooling calculations including benchmarking experiments and development of a large superconducting solenoid. The photoinjector and linac cavity are being incorporated into an energy recovery linac aimed at demonstrating ampere class current at about 20 MeV. A Zeroth Order Design Report is in an advanced draft state, and can be found on the web at http://www.agsrhichome.bnl.gov/eCool/.
Under contract with the U.S. Department of Energy, Contract Number DE-AC02-98CH10886. |
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| TPAT081 | Observation of Electron-Ion Effects at RHIC Transition | 4087 |
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Funding: Work performed under the auspices of the U.S. Department of Energy. Electron cloud is found to be a serious obstacle on the upgrade path of the Relativistic Heavy Ion Collider (RHIC). At twice the design number of bunches, electron-ion interactions cause significant instability, emittance growth, and beam loss along with vacuum pressure rises when the beam is accelerated across the transition. |
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| TPAT093 | Operations and Performance of RHIC as a Cu-Cu Collider | 4281 |
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Funding: Work performed under the auspices of the U.S. Department of Energy. The 5th year of RHIC operations, started in November 2004 and expected to last till June 2005, consists of a physics run with Cu-Cu collisions at 100 GeV/u followed by one with polarized protons at 100 GeV. We will address here overall performance of the RHIC complex used for the first time as a Cu-Cu collider, and compare it with previous operational experience with Au, PP and asymmetric d-Au collisions. We will also discuss operational improvements, such as a ?* squeeze to 85cm in the high luminosity interaction regions from the design value of 1m, system improvements and machine performance limitations, such as vacuum pressure rise, intra-beam scattering, and beam beam interaction. |
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| TPAT095 | Beam Induced Pressure Rise at RHIC | 4308 |
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Beam induced pressure rise in RHIC warm sections is currently one of the machine intensity and luminosity limits. This pressure rise is mainly due to electron cloud effects. The RHIC warm section electron cloud is associated with longer bunch spacings compared with other machines, and is distributed non-uniformly around the ring. In addition to the countermeasures for normal electron cloud, such as the NEG coated pipe, solenoids, beam scrubbing, bunch gaps, and larger bunch spacing, other studies and beam tests toward the understanding and counteracting RHIC warm electron cloud are of interest. These include the ion desorption studies and the test of anti-grazing ridges. For high bunch intensities and the shortest bunch spacings, pressure rises at certain locations in the cryogenic region have been observed during the past two runs. Beam studies are planned for the current 2005 run and the results will be reported.
Work performed under the auspices of the US Department of Energy. |
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| TPPP022 | The eRHIC Ring-Ring Collider Design | 1766 |
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| The eRHIC ring-ring collider is the main design option of the future lepton-ion collider at Brookhaven National Laboratory. We report the revisions of the ring-ring collider design features to the baseline design presented in the eRHIC Zeroth Design Report (ZDR). These revisions have been made during the past year. They include changes of the interaction region which are required from the modifications in the design of the main detector. They also include changes in the lepton storage ring for high current operations as a result of better understandings of beam-beam interaction effects. The updated collider luminosity and beam parameters also take into account a more accurate picture of current and future operational aspects of RHIC. | ||
| TPPP043 | ERL Based Electron-Ion Collider eRHIC | 2768 |
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Funding: Work performed under Contract Number DE-AC02-98CH10886 with the auspices of the US Department of Energy. We present the designs of a future polarized electron-hadron collider, eRHIC* based on a high current super-conducting energy-recovery linac (ERL) with energy of electrons up to 20 GeV. We plan to operate eRHIC in both dedicated (electron-hadrons only) and parallel(with the main hadron-hadron collisions) modes. The eRHIC has very large tunability range of c.m. energies while maintaining very high luminosity up to 1034 cm-2 s-1 per nucleon. Two of the most attractive features of this scheme are full spin transparency of the ERL at all operational energies and the capability to support up to four interaction points. We present two main layouts of the eRHIC, the expected beam and luminosity parameter, and discuss the potential limitation of its performance. *http://www.agsrhichome.bnl.gov/eRHIC/, Appendix A: Linac-Ring Option. |
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| RPPE009 | Extremely High Current, High-Brightness Energy Recovery Linac | 1150 |
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Funding: Under contract with the U.S. Department of Energy, U.S. DOD Office of Naval Research and Joint Technology Office. Next generation ERL light-sources, high-energy electron coolers, high-power Free-Electron Lasers, powerful Compton X-ray sources and many other accelerators were made possible by the emerging technology of high-power, high-brightness electron beams. In order to get the anticipated performance level of ampere-class currents, many technological barriers are yet to be broken. BNL’s Collider-Accelerator Department is pursuing some of these technologies for its electron cooling of RHIC application, as well as a possible future electron-hadron collider. We will describe work on CW, high-current and high-brightness electron beams. This will include a description of a superconducting, laser-photocathode RF gun and an accelerator cavity capable of producing low emittance (about 1 micron rms normalized) one nano-Coulomb bunches at currents of the order of one ampere average. |
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| RPPT032 | High Current Energy Recovery Linac at BNL | 2242 |
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Funding: Work performed under Contract Number DE-AC02-98CH10886 with the auspices of the U.S. Department of Energy. We present the design and the parameters of a small Energy Recovery Linac (ERL) facility, which is under construction at BNL. This R&D facility has goals to demonstrate CW operation of ERL with average beam current in the range of 0.1 - 1 ampere, combined with very high efficiency of energy recovery. The possibility for future up-grade to a two-pass ERL is being considered. The heart of the facility is a 5-cell 703.75 MHz super-conducting RF linac with HOM damping. Flexible lattice of ERL provides a test-bed for testing issues of transverse and longitudinal instabilities and diagnostics of intense CW e-beam. We present the status and plans for this facility. |
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| FPAE006 | Optimization of AGS Polarized Proton Operation with the Warm Helical Snake | 1003 |
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Funding: US DOE and RIKEN Japan. A normal conducting helical dipole partial Siberian snake (Warm Snake) has been installed in the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL) for overcoming all of imperfection depolarizing resonances and reducing the transverse coupling resonances caused by the solenoidal Siberian snake which had been operated in AGS before the last polarized run. The polarized proton beam has been accelerated successfully with the warm snake and the polarization at extraction of the AGS was increased to 50% as opposed to 40% with the solenoidal snake. The magnetic field and beam trajectory in the warm snake was calculated by using the OPERA-3D/TOSCA software. We present optimization of the warm snake with beam during RUN5. |
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| FPAE014 | Acceleration of Polarized Protons in the AGS with Two Helical Partial Snakes | 1404 |
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Funding: Work supported by U.S. DOE and RIKEN of Japan. The RHIC spin program requires 2*1011 proton/bunch with 70% polarization. As the injector to RHIC, AGS is the bottleneck for preserving polarization: there is not enough space in the ring to install a full snake to overcome the numerous depolarizing resonances. An ac dipole and a partial Siberian snake have been used to preserve beam polarization in the past. The correction with this scheme is not 100% since not all depolarizing resonances can be overcome. Recently, two helical snakes with double pitch design have been built and installed in the AGS. With careful setup of optics at injection and along the ramp, this combination can eliminate all depolarizing resonances encountered during acceleration. This paper presents the accelerator setup and preliminary results. |
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| FPAE029 | Setup and Performance of the RHIC Injector Accelerators for the 2005 Run with Copper Ions | 2068 |
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Funding: Work performed under the auspices of the U.S. Department of Energy. Copper ions for the 2005 run of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory 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. |