BNL, Upton, Long Island, New York, USA
RHIC operation as the polarized proton collider presents unique challenges since both luminosity and spin polarization are important. With longitudinally polarized beams at the experiments, the figure of merit is LP4. A lot of upgrades and modifications have been made since last polarized proton operation. A 9 MHz rf system has been installed to improve longitudinal match at injection and to increase luminosity. The beam dumps were upgraded to allow for increased bunch intensities. A vertical survey of RHIC was performed before the run to get better magnet alignment. The orbit control has also been improved this year. Additional efforts were put in to improve source polarization and AGS polarization transfer efficiency. To preserve polarization on the ramp, a new working point was chosen such that the vertical tune is near a third order resonance. The overview of the changes and the operation results are presented in this paper.
BNL, Upton, Long Island, New York, USA
Power Supply checkout is a necessary, pre-beam, time-critical function. At odds are the desire to decrease the amount of time to perform the checkout while at the same time maximizing the number and types of checks that can be performed and analyzing the results quickly (in case any problems exist that must be addressed). Controls and Power Supply Group personnel have worked together to develop tools to accomplish these goals. Power Supply checkouts are now accomplished in a time-frame of hours rather than days, reducing the number of person-hours needed to accomplish the checkout and making the system available more quickly for beam development.
BNL, Upton, Long Island, New York, USA
In order to cool the superconducting magnets in RHIC, its helium refrigerator distributes 4.5 K helium throughout the tunnel via a series of distribution and return lines. The worst case for failure would be a release from the magnet distribution line, which operates at 3.5 to 4.5 atmospheres and contains the energized magnet bus. Should the bus insulation system fail or an electrical connection open, there is the potential for releasing up to 70 MJoules of stored energy. Studies were done to determine release rate of the helium and the resultant reduction in O2 concentration in the RHIC tunnel and service buildings. Equipment and components were also reviewed for reliability and the effects of 10 years of operations. Modifications were made to reduce the likelihood of failure and to reduce the amount of helium gas that could be released into tunnels and service buildings while personnel are present. This paper describes the issues reviewed, the steps taken, and remaining work to be done to reduce the hazards.
BNL, Upton, Long Island, New York, USA
As part of the search for a phase transition or critical point on the QCD phase diagram, an energy scan including 5 different energy settings was performed during the 2010 RHIC heavy ion run. While the top beam energy for heavy ions is at 100 GeV/n and the lowest achieved energy setpoint was significantly below RHICs injection energy of approximately 10 GeV/n, we also provided beams for data taking in a medium energy range above injection energy and below top beam energy. This paper reviews RHIC experience and challenges for RHIC medium energy operations that produced full experimental data sets at beam energies of 31.2 GeV/n and 19.5 GeV/n.
BNL, Upton, Long Island, New York, USA
Two electron lenses are under construction for RHIC to partially compensate the head-on beam-beam effect in order to increase both the peak and average luminosity. The final design of the overall system is reported as well as the status of the component design, acquisition, and manufacturing.
BNL, Upton, Long Island, New York, USA
There are 60 12×150A current leads distributed in 6 RHIC service buildings; each current lead delivers power supply current from room temperature to cryogenic temperature in RHIC. Due to the humid environment, condensation frequently occurs and ice was quickly formed during operation, especially during an extensive storage period. This condition generated warnings and alarms that personal had to respond to, in order to provide temporary solutions, to keep the machine operational. A temperature control system was designed to avoid such occasions. We will discuss design, implementation and some results of this design in this paper.
BNL, Upton, Long Island, New York, USA
RHIC operated at energies below the nominal ion injection energy of E=9.8 GeV/u in 2010. Earlier test runs and magnet measurements indicated that all defocusing sextupole unipolar power supplies should be reversed to provide the proper sign of chromaticity. However, vertical chromaticity at E=3.85 GeV/u with this power supply configuration was still not optimal. This uncertainty inspired a new machine configuration where only half of the defocusing sextupole power supplies were reversed, taking advantage of the flexibility of the RHIC nonlinear chromaticity correction system to mimic bipolar sextupoles. This configuration resulted in a 30 percent luminosity gain and eliminated the need for further polarity changes for later 2010 low energy physics operations. Here we describe the background to this problem, operational experience, and RHIC online model changes to implement this solution.