BNL, Upton, Long Island, New York, USA
To search for the critical point in the QCD phase diagram, Au-Au collisions at beam energies between 2.5 and 15 GeV are required. While RHIC has successfully operated at 3.85 and 5.75 GeV, the performance achieved at 2.5 GeV is not sufficient for a meaningful physics program. We report on dedicated beam experiments performed to understand and improve this situation.
BNL, Upton, Long Island, New York, USA
In the 2013 RHIC polarized proton run, it was found that the RHIC bunch intensity has reached a limit due to the head-on beam-beam interaction at 2x1011, as expected by simulations. To overcome this limitation, two electron lenses will be used for compensation. We report on the commissioning of new lattices that reduce beam-beam driven resonance driving terms, and bunch-by-bunch proton diagnostic during 2013 run. The effect of electron beam transport solenoids on the proton orbit was tested. The instrumentation for Blue electron lens was tested and electron beam was propagated from the gun to the collector. A timing system was implemented for the electron beam. Control software, machine protection and synoptic display were developed and tested during commissioning. Both Blue and Yellow electron lens superconducting magnets are installed and their field straightness was measured and corrected in the tunnel using a magnetic needle. The Yellow vacuum system and backscattered electron detectors installation are also completed now.
BNL, Upton, Long Island, New York, USA
In the next 5-10 years, RHIC will be colliding gold ions in the center-of-mass energy range of 5 to 20 GeV, which is below the regular injection energy. Though the machine has already successfully provided collisions at CM-energies of 7.7 and 11.5 GeV, a significantly higher luminosity than so far achieved is required for a meaningful physics program. While an electron cooler is presently being designed to provide the desired luminosity gain, this is a long-term project that is expected to be completed in 2018. As a short-term alternative the STAR collaboration has proposed installation of an internal halo target in the STAR detector beam pipe. To study the generation and control of the beam halo, we have performed dedicated beam experiments aimed at the bunch-by-bunch uniformity, and long as well as short-term stability of collimator loss rates.
BNL, Upton, Long Island, New York, USA
To commission some of the hard and software for the RHIC electron lenses (e-lenses), a test bench was built based on the EBIS test stand at BNL. After several months of operation, the electron gun, collector, high-voltage gun modulator, instrumentation, partial control system, and several software applications have been tested. The nominal DC beam current of 0.85 A was demonstrated and the electron beam transverse profiles were verified to be Gaussian. Some e-lens power supplies and the electronics for current measurement were also evaluated on the test bench. The properties of the cathode and the profile of the beam are measured. In this paper, we will present some experimental results.
BNL, Upton, Long Island, New York, USA
Mechanical analysis of the RHIC beam dump window has shown that present heavy ion beam intensities are close to the tolerable limit, and will likely exceed that limit in future runs. Different approaches to upgrade the abort system for those projected higher intensities have been studied, namely replacing the existing window, and adding a vertical kicker that distributes the individual bunches more evenly across the window, thus reducing the heat load. We present the results of these studies and the present status of the upgrade project.