BNL, Upton, Long Island, New York, USA
The head-on beam-beam interaction is the dominant luminosity limiting effect in polarized proton operation in RHIC. To mitigate this effect two electron lenses were installed in the two RHIC rings. We summarize the hardware and electron beam commissioning results to date, and report on the first experience with the electron-hadron beam interaction. In 2014 RHIC is operating with gold beams only. In this case the luminosity is not limited by head-on beam-beam interactions and compensation is not necessary. The goals of this year’s commissioning efforts are a test of all instrumentation; the demonstration of electron and gold beam overlap; the demonstration of electron beam parameters that are sufficiently stable to have no negative impact on the gold beam lifetime; and the measurement of the tune footprint compression from the beam overlap. With these demonstrations, and a lattice with a phase advance that has a multiple of 180 degrees between the beam-beam interaction and electron lens locations, head-on beam-beam compensation can be commissioned in the following year with proton beams.
BNL, Upton, Long Island, New York, USA
As the last missing step in phase 1 of the beam energy scan (BES-I), aimed at the search for the critical point in the QCD phase diagram, RHIC collided gold ions at a beam energy of 7.3 GeV/nucleon during the FY 2014 run. While this particular energy is close to the nominal RHIC injection energy of 9.8 GeV/nucleon, it is nevertheless challenging because it happens to be close to the AGS transition energy, which makes longitudinal beam dynamics during transfer from the AGS to RHIC difficult. We report on machine performance, obstacles and solutions during the FY 2014 low energy run.
BNL, Upton, Long Island, New York, USA
After running uranium-uranium and copper-gold collisions in 2012, the high energy heavy ion run of the Relativistic Heavy Ion Collider (RHIC) for Fiscal Year 14 (Run14) is back to gold-gold (Au-Au) collisions at 100 GeV/nucleon. Following the level of performance achieved in Run12, RHIC is still looking to push both instantaneous and integrated luminosity goals. To that end, a new 56 MHz superconducting RF cavity was installed and commissioned, designed to keep ions in one RF bucket and improve luminosity by allowing a smaller beta function at the interaction point (IP) due to a reduced hourglass effect. The following presents an overview of these changes and reviews the performance of the collider.
BNL, Upton, Long Island, New York, USA
In this article, we study the beam-beam interaction in the possible future gold-gold collision with different particle energies in the Relativistic Heavy Ion Collider (RHIC). With different particle energies, the center-of-mass of collision is moving in the longitudinal direction during collision. Since the RF harmonic numbers are different for the two RHIC rings, bunches collide in 110 turns followed by 10 turns without collision. In this study, the stability of particles and the beam emittance growth are calculated through numeric simulations based on a 6-D weak-strong beam-beam interaction model.
BNL, Upton, Long Island, New York, USA
Imperfection and vertical intrinsic depolarizing resonances have been overcome by the two partial Siberian snakes in the AGS. The relatively weak but numerous horizontal resonances are the main source of polarization loss in the AGS. A pair of horizontal quads have been used to overcome these weak resonances. This technique needs very accurate jump timing. Fast roll-over magnet cycle has been used and it improves the polarization transmission efficiency near extraction when acceleration usually is slowing down. Emittance preservation is also important to mitigate polarization loss. Recent experimental results including jump quad timing and emittance preservation are presented in this paper.
BNL, Upton, Long Island, New York, USA
Future RHIC physics program calls for polarized He3 beam. The He3 beam from the new EBIS source has a relative low rigidity which requires delicate control of injection and RF setup in the Booster. The strong depolarization resonance strength in both AGS and AGS Booster requires careful consideration of beam energy range and optics setup. Recently, the He3 beam was accelerated to 11GeV/n in the AGS. The near term goal fo 3*1010 at RHIC requires several RF bunch merges in both AGS and the Booster. The beam test results are presented in this paper.
BNL, Upton, Long Island, New York, USA
PVI, Oxnard, California, USA
To alleviate the problems of unacceptable ohmic heating and of electron clouds, a 50 cm long cathode magnetron mole was fabricated and successfully operated to copper coat an assembly containing a full-size stainless steel cold bore RHIC magnet tubing connected to two types of RHIC bellows, to which two additional RHIC tubing pipes were connected. To increase cathode lifetime, movable magnet package was developed, and thickest possible cathode was made, with rather challenging target to substrate distance of less than 1.5 cm. The magnetron is mounted on a carriage with spring loaded wheels that successfully crossed bellows and adjusted for variations in vacuum tube diameter, while keeping the magnetron centered. Electrical power and cooling water are fed through a motorized spool driven umbilical cabling system, which is enclosed in a flexible braided metal sleeve. Optimized process to ensure excellent adhesion was developed. Coating adhesion of 10 μm Cu surpassed all industrial tests; exceeded maximum capability of a 12 kg pull test fixture. Details of experimental setup for coating two types of bellows and a full-scale magnet tube sandwiched between them will be presented.
TEMF, TU Darmstadt, Darmstadt, Germany
BNL, Upton, Long Island, New York, USA
BNL, Upton, Long Island, New York, USA
PVI, Oxnard, California, USA
An in-situ technique for coating stainless steel vacuum tubes with Cu was developed to mitigate the problems of wall resistivity that leads to unacceptable ohmic heating of superconducting magnets cold bore and electron cloud generation in RHIC that can limit future machine luminosity enhancement. Room temperature RF resistivity of 10 μm Cu coated stainless steel RHIC beam tube has conductivity close to copper tubing. Before coating the RHIC beam pipe with copper, it is imperative to test the Cu coating’s conductivity at cryogenic. A folded quarter wave resonator structure has been designed and built for insertion in a cryogenic system to measure RF resistivity of copper coated RHIC tubing at liquid helium temperatures. The design is based on making the resonator structure out of a superconducting material such that the copper coating is the most lossy material. RHIC tubing samples prepared with different magnetron sputtering deposition modes are to be optimized by iterative processes. Additionally, this device can also be used for the development of better, cheaper SRF cavities and electron guns. The apparatus and its design details will be presented.