BNL, Upton, Long Island, New York, USA
In this article we calculate and compare the off-momentum dynamic aperture for lattices with different phase advances per FODO cell in the RHIC heavy ion runs. A lattice with an increased phase advance was adopted in 2008-2011 to reduce transverse emittance growth rates from intra-beam scattering. However, during these runs, a large beam loss was observed with longitudinal RF re-bucketing which increased the momentum spread. With operational transverse stochastic cooling in the 2011 RHIC heavy ion run, the transverse intra-beam scattering emittance growth was eliminated, and the beam loss during stores was determined by the off-momentum aperture and burn-off from luminosity. We investigate the possibilities to increase the off-momentum dynamic aperture that would lead to an increase in the integrated luminosity.
BNL, Upton, Long Island, New York, USA
Electron lenses are foreseen to be installed in RHIC in order to mitigate the head-on beam-beam effects. This would allow operation with higher bunch intensity and result in a significant increase in luminosity. We report on recent strong-strong simulations that were carried out using the RHIC upgrade parameters to assess the impact of coherent beam-beam effects in the presence of head-on compensation.
BNL, Upton, Long Island, New York, USA
In polarized proton operation in RHIC coherent beam-beam modes are routinely observed with beam transfer function measurements in the vertical plane. With the existence of coherent modes a larger space is required in the tune diagram than without them and stable conditions can be compromised for operation with high intensity beams as foreseen for future luminosity upgrades. We report on experiments and simulations carried out to understand the existence of coherent modes in the vertical plane and their absence in the horizontal plane, and investigate possible mitigation strategies.
BNL, Upton, Long Island, New York, USA
In this article we will present the measurement and correction of the off-momentum β*-beat in the RHIC proton run. The beta-beat will be measured with the AC dipole and by shifting RF frequency. We will focus on the correction of the off-momentum beta-beat at the interaction points IP6 and IP8 with the arc chromatic sextupole families. The effects of the off-momentum beta-beat correction on the global chromaticities and dynamic aperture will be estimated through beam experiments and the numerical simulation.
BNL, Upton, Long Island, New York, USA
BNL, Upton, Long Island, New York, USA
CERN, Geneva, Switzerland
The further improvement of RHIC luminosity performance requires more precise understanding of the RHIC modeling. Hence, it is necessary to minimize the beta-beat, deviation of measured beta function from the calculated beta functions based on an model. The correction of beta-beat also opens up the possibility of exploring operating RHIC polarized protons at a working point near integer, a preferred choice for both luminosity as well as beam polarization. The segment-by-segment technique for reducing beta-beat demonstrated in the LHC operation for reducing the beta-beat was first tested in RHIC during its polarized proton operation in 2011. It was then fully implemented during the RHIC polarized proton operation in 2012. This paper reports the commissioning results. Future plan is also presented.
BNL, Upton, Long Island, New York, USA
In polarized proton operation, the RHIC performance is limited by the head-on beam-beam effect. To overcome these limitations two electron lenses are under construction. We give an overview of the progress over the last year. Guns, collectors and the warm electron beam transport solenoids with their associated power supplies have been constructed. The superconducting solenoids that guide the electron beam during the interaction with the proton beam are near completion. A test stand has been set up to verify the performance of gun, collector and some of the instrumentation. The RHIC infrastructure is being prepared for installation, and simulations continue to optimize the performance.
BNL, Upton, Long Island, New York, USA
To compensate for the beam-beam effects from the proton-proton interactions at IP6 and IP8 in the Relativistic Heavy Ion Collider (RHIC), we are fabricating two electron lenses that we plan to install at RHIC IR10. Before installing the e-lenses, we are setting-up the e-lens test bench to test the electron gun, collector, GS1 coil, modulator, partial control system, some instrumentation, and the application software. Some e-lens power supplies, the electronics for current measurement will also be qualified on test bench. The test bench also was designed for measuring the properties of the cathode and the profile of the beam. In this paper, we introduce the layout and elements of the e-lens test bench; and we discuss its present status towards the end of this paper.
BNL, Upton, Long Island, New York, USA
Residual vertical dispersion on the order of ±0.2 m (peak to peak) has been measured at store energies for both polarized proton and heavy ion beams. The hypothesis is that this may have impact on the polarization transmission efficiency during the energy ramp, the beam lifetimes, and, especially for heavy ions, the dynamics aperture. An algorithm to correct global coupling and dispersion simultaneously using skew quads was developed for RHIC. Simulation results together with the measured coupling and dispersion functions before and after correction will be shown for both injection and store together with an assessment of overall collider performance improvement.
BNL, Upton, Long Island, New York, USA
We are designing two electron lenses that will be installed at RHIC IR10 to compensate for the head-on beam-beam effect. To clear accumulated scattered electrons from 100 GeV proton-electron head-on collisions in the e-lens, a clearing split electrode may be constructed. The feasibility of this proposed electrode was demonstrated via the CST Particle Studio and Opera program simulations. By splitting one of the drift tubes in the e-lens and applying ~ 380 V across the two parts, the scattered electrons can be cleared out within several hundred micro-seconds. At the same time we can restrict the unwanted shift of the primary electron-beam that already passed the 2-m interaction region in e-lens, to less than 15um.
DULY Research Inc., Rancho Palos Verdes, California, USA
Fermilab, Batavia, USA
An L-band, 1+2/2-cell PWT gun with a coax coupler has been designed for high vacuum polarized electron source applications by DULY Research Inc. A cold test model was fabricated and is currently undergoing test at Fermilab, where the gun will eventually be hot tested. The aluminum cold test model includes an rf/ vacuum sieve, 2 disks, endplates, 6 supporting rods and a 6” CF flange, clamped together during testing. Fermilab made measurements for the cavity resonant frequency and axial field distribution using bead pull. To measure the resonant frequency of the cavity small diameter probes are placed through the vacuum sieve slot. A larger diameter probe can be used as an active tuner. This paper presents the results of the cold test and compares measurements with simulation results from 3D SLAC code Omega3p. The axial field distributions are in good agreement with each other. Frequency deviation is less than 0.5%, well within the experimental accuracy.