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
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.
IUCEEM, Bloomington, Indiana, USA
BNL, Upton, Long Island, New York, USA
CERN, Geneva, Switzerland
Independent component analysis (ICA) was applied to the AC dipole based optics measurement at RHIC to extract beta functions as well as phase advances at each BPM. Existence of excessive beta-beat was observed in both rings of RHIC at store energy. A unique global optics correction scheme was then developed and tested successfully during the RHIC polarized proton run in 2013. The feasibility of using closed orbit bump and sextupole for arc beta-beat correction was also demonstrated. The technique and experimental results of optics correction are reported in this paper.
BNL, Upton, Long Island, New York, USA
To minimize the large beam-beam tune spread and to reduce the beam-beam nonlinear resonance driving terms, two electron lenses are being installed in the RHIC tunnel for head-on beam-beam compensation. In this article we discuss the approaches to maximize the proton dynamic aperture by adjusting the phase advances between beam-beam interaction points, and the phase advances between the beam-beam interaction points and the electron lenses, and by choosing different β*s at the beam-beam interaction points.
BNL, Upton, Long Island, New York, USA
Relativistic Heavy Ion Collider (RHIC) has been achieving record luminosities during the last decade. The latest stochastic cooling of the heavy ions like uranium achieved the largest luminosity at RHIC during the last heavy ion run. A betatron squeeze method, already used at LHC CERN, where a betatron wave is created through the arc up to the interaction region is applied at RHIC. When the heavy beam size is reduced due to stochastic cooling a dynamical beta squeeze is possible to apply in RHIC where the existing 80 cm value of beta-star could be reduced to 40 cm. This could be achieved by introducing the betatron wave in both planes throughout the arc before and after the interaction region. Higher values of dispersion and betatron functions in the arc, with a 90 degrees phase difference per FODO cell allow easier higher order chromatic corrections.
BNL, Upton, Long Island, New York, USA
A proposal for the new high luminosity L=1034 s-1 cm-2, polarized electron proton/3He and other un-polarized heavy ions eRHIC based on Electron Recovery Linacs (ERL), assumes a location in the existing tunnel of the operating Relativistic Heavy Ion Collider (RHIC). Requests of the experiments for the interaction region are very challenging: allow detection of neutrons, allow deep virtual scattering for protons-electron collisions, detection of partons with lower momentum, etc. We present an interaction region (IR) design with a vey high focusing where at the collision point IP of 5 cm, and a 10 mrad collision angle between electrons and ions using the crab cavities. We are introducing a combined function magnet for the first element in the high focusing triplet configuration to provide neutron and the lower energy parton detection, and allow at 4.5 cm distance passage of electrons through a no magnetic field region. The 200 T/m gradient quadrupoles provide very small beam size at the IP and allows a passage with a very small magnetic field for electrons.
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.