BNL, Upton, Long Island, New York, USA
Over the past several years, the installation of the full 3-dimensional stochastic cooling system in RHIC has been completed. The FY12 U-U and Cu-Au collider runs were the first to benefit from the full installation. In the U-U run, stochastic cooling improved the integrated luminosity by a factor of 5. This presentation provides an overview of the design of the stochastic cooling system and reviews the performance of the system during the FY12 heavy ion runs.
BNL, Upton, Long Island, New York, USA
In the 2012 RHIC heavy ion run, we collided uranium-uranium (U-U) ions at 96.4~GeV/nucleon and copper-gold (Cu-Au) ions at 100~GeV/nucleon for the first time in RHIC. The new Electron-Beam Ion Source (EBIS) was used for the first time to provide ions for the RHIC physics program. After adding the horizontal cooling, 3-D stochastic cooling became operational in RHIC for the first time, which greatly enhanced the luminosity. In this article, we first review the improvements and performances in the 2012 RHIC ion runs. Then we discuss the conditions and approaches to achieve the burn-off dominated Uranium beam lifetime at physics stores. And we discuss the asymmetric copper-gold collision due to different IBS and stochastic cooling rates, and the operational solutions to maximize the integrated luminosity.
BNL, Upton, Long Island, New York, USA
Based on the beam emittance measurement from the pickup, the RHIC Stochastic Cooling kicker uses sixteen narrowband high Q cavities (from 5 to 8 GHz) to kick (or to cool) the bunched beam on each of the two transverse planes in the two rings. The cavities are integrated to two pairs of cavity plates and installed in two UHV chambers. The new kicker features scissor like driving mechanism, frictionless flexure joints, water cooled cavity plates, small frequency shift (less than 0.05%) during the operation and maintenance free. Novel mechanical designs, including cavity plate, vacuum, cooling, driving mechanism, and support structure design, are presented. Structural and thermal analyses, using ANSYS, were performed to confirm chamber structural stability and to calculate the cavity plate deformation due to thermal and mechanical load. Good agreement between the calculated cavity plate deflection and the expected plate deformation from the cavity frequency shift measurements has been achieved. Three assemblies utilizing this design (1 for the vertical and 2 for the horizontal plane) were completed for the FY2012 run. Successful performance has been reported.
BNL, Upton, Long Island, New York, USA
The RHIC transverse Stochastic Cooling Pickup uses a pair of high resolution 4-8 GHz frequency band planar loop arrays to measure the Schottky signals from the bunched beams in the two transverse planes of the two rings. Precision alignment between the two 381 mm long array boards was achieved by surveying two specially designed target fixtures outside the vacuum chamber and using a pair of high resolution, motor controlled, and force balanced actuators. Robust mechanical design was achieved by excluding wearable mechanical joints and fragile electronics inside the vacuum chamber. Both mechanical designs and structural analysis results, for the vacuum chamber and for the array board supports, are presented. Two horizontal and two vertical plane pickups have been fabricated and installed in RHIC for the FY2012 run. Successful performance has been reported.
BNL, Upton, Long Island, New York, USA
The signal cables from the beam position monitors (BPMs) in the cryogenic sections of RHIC need to satisfy somewhat conflicting requirements. On the one hand, the cryogenic load due to heat conduction along the cable needs to be small, which led to the use of stainless steel jacketed cables with Tefzel insulation. On the other hand, radio frequency losses need to be reasonably small to reduce heating due to dissipated signal power. As the beam intensity in RHIC increased over the years, and the bunches become shorter, a point is being rapidly approached where these cables will soon become a performance limiting factor. Here we describe an extensive study of this problem including cable loss measurements as a function of temperature and frequency, characterization of the copper center conductor, and Particle Studio and ANSYS simulations.