BNL, Upton, Long Island, New York
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
After having provided collisions of polarized protons at a beam energy of 100 GeV since 2001, the Relativistic Heavy Ion Collider~(RHIC) at BNL reached its design energy of polarized proton collision at 250 GeV. With the help of the two full Siberian snakes in each ring as well as careful orbit correction and working point control, polarization was preserved during acceleration from injection to 250~GeV. During the course of the Physics data taking, the spin rotators on either side of the experiments of STAR and PHENIX were set up to provide collisions with longitudinal polarization at both experiments. Various techniques to increase luminosity like further beta star squeeze and RF system upgrades as well as gymnastics to shorten the bunch length at store were also explored during the run. This paper reports the performance of the run as well as the plan for future performance improvement in RHIC.
BNL, Upton, Long Island, New York
PVI, Oxnard
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
Electron clouds have been observed in many accelerators, including RHIC at BNL. They can limit the machine performance through pressure degradation, beam instabilities or incoherent emittance growth. The formation of electron clouds can be suppressed with beam pipe surfaces that have low secondary electron yield. Also, high wall resistivity in accelerators can result in unacceptably high ohmic heating levels for superconducting magnets. These are concerns RHIC, as its vacuum chamber in the superconducting dipoles is made from relatively high resistivity 316LN stainless steel. The high resistivity can be addressed with a copper (Cu) coating; a reduction in the secondary electron yield can be achieved with a titanium nitride (TiN) or amorphous carbon (a-C) coating. Applying such coatings in an already constructed machine is rather challenging. We sta rted developing a robotic plasma deposition technique for in-situ coating of long, small diameter tubes. The technique entails fabricating a device comprising of staged magnetrons and/or cathodic arcs mounted on a mobile mole for deposition of about 5 μm (a few skin depths) of Cu followed by about 0.1 μm of TiN (or a-C).
BNL, Upton, Long Island, New York
Funding: Department Of Energy
Under certain assumptions and simplifications, we studied a few physics processes of Coherent Electron Cooling using analytical approach. In the modulation process, the effect due to merging the ion beam with the electron beam is studied under single kick approximation. In the FEL amplifier, we studied the amplification of the electron density modulation using 1D analytical approach. Both the electron charge density and the phase space density are derived in the frequency domain. The solutions are then transformed into the space domain through Fast Fourier Transformation (FFT).
BNL, Upton, Long Island, New York
After the success of longitudinal stochastic cooling of bunched heavy ion beam in RHIC, transverse stochastic cooling was installed and commissioned with proton beam. The talk presents the status of this effort and gives an estimate, based on simulation, of the RHIC luminosity with stochastic cooling in all planes.
BNL, Upton, Long Island, New York
The luminosity of the eRHIC ring-ring design is limited by the beam-beam effect exerted on the electron beam. Recent simulation studies have shown that the beam-beam limit can be increased by means of an electron lens that compensates the beam-beam effect experienced by the electron beam. This scheme requires proper design of the electron ring, providing the correct betatron phase advance between interaction point and electron lens. We review the performance of the eRHIC ring-ring version and discuss various parameter sets, based on different cooling schemes for the proton/ion beam.
BNL, Upton, Long Island, New York
In this report we summarize electron-cloud simulations for the RHIC dipole regions at injection and transition to estimate if scrubbing at injection would reduce the electron cloud density at transition. We simulate the horizontal electron cloud distribution in the RHIC dipoles for secondary electron yields (SEY) from 1.1 to 2.0 at injection (with a bunch intensity of 1.3x109) and at transition (with a bunch intensity of 1.2x109). Also, we unveil the sensitivity to rather small changes in bunch intensity from 1.0 x109 to 1.5x109 , when SEY keep at 1.4 and 1.5 both for injection and transition.
BNL, Upton, Long Island, New York
Funding: Work supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the U.S. Department of Energy
Couples bunch longitudinal instability in the presence of high frequency impedance is considered. A frequency domain technique is developed and compared with simulations. The frequency domain technique allows for absolute stability tests and is applied to the problem of longitudinal stability in RHIC with the proposed 56 MHz rf system.