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Stochastic cooling of a high energy collider

Description: Gold beams in RHIC revolve more than a billion times over the course of a data acquisition session or store. During operations with these heavy ions the event rates in the detectors decay as the beams diffuse. A primary cause for this beam diffusion is small angle Coloumb scattering of the particles within the bunches. This intra-beam scattering (IBS) is particularly problematic at high energy because the negative mass effect removes the possibility of even approximate thermal equilibrium. Stochastic cooling can combat IBS. A theory of bunched beam cooling was developed in the early eighties and stochastic cooling systems for the SPS and the Tevatron were explored. Cooling for heavy ions in RHIC was also considered.
Date: September 4, 2011
Creator: Blaskiewicz, M.; Brennan, J.M.; Lee, R.C. & Mernick, K.
Partner: UNT Libraries Government Documents Department

Stochastic cooling in RHIC

Description: The full 6-dimensional [x,x'; y,y'; z,z'] stochastic cooling system for RHIC was completed and operational for the FY12 Uranium-Uranium collider run. Cooling enhances the integrated luminosity of the Uranium collisions by a factor of 5, primarily by reducing the transverse emittances but also by cooling in the longitudinal plane to preserve the bunch length. The components have been deployed incrementally over the past several runs, beginning with longitudinal cooling, then cooling in the vertical planes but multiplexed between the Yellow and Blue rings, next cooling both rings simultaneously in vertical (the horizontal plane was cooled by betatron coupling), and now simultaneous horizontal cooling has been commissioned. The system operated between 5 and 9 GHz and with 3 x 10{sup 8} Uranium ions per bunch and produces a cooling half-time of approximately 20 minutes. The ultimate emittance is determined by the balance between cooling and emittance growth from Intra-Beam Scattering. Specific details of the apparatus and mathematical techniques for calculating its performance have been published elsewhere. Here we report on: the method of operation, results with beam, and comparison of results to simulations.
Date: May 20, 2012
Creator: M., Brennan J.; Blaskiewicz, M. & Mernick, K.
Partner: UNT Libraries Government Documents Department

Near real-time ORM measurements and SVD matrix generation for 10 Hz global orbit feedback in RHIC

Description: To reduce the effect of trajectory perturbations ({approx}10 Hz) due to vibrations of the final focusing quadrupoles at RHIC, global orbit feedback was successfully prototyped during run-10. After upgraded to a system with 36 BPMs and 12 correctors, 10 Hz feedback was tested successfully in Run-11 and is in operational status for physics program. The test and operation of the system has been performed using transfer functions between the beam position monitors and correctors obtained from the online optics model and a correction algorithm based on singular value decomposition (SVD). One of our goals is to self-calibrate the system using SVD matrices derived from orbit response matrix (ORM) measurements acquired real-time using the new FPGA-based signal processing. Comparisons between measurement matrix and model matrix and the generation of SVD matrix for the feedback operation are presented.
Date: March 28, 2011
Creator: Liu, C.; Hulsart, R.; MacKay, W.; Marusic, A.; Mernick, K.; Michnoff, R. et al.
Partner: UNT Libraries Government Documents Department

Off-momentum beta-beat correction in the RHIC proton run

Description: In this article, we will review the techniques to measure the off-momentum {beta}-beat and the correction algorithms with the chromatic arc sextupoles in RHIC. We will focus on the measurement and correction of the off-momentum {beta}*-beat at the interaction points. The off-momentum {beta}* is measured with the quadrupole strength change and a high resolution phase lock loop tune meter. The results of off-momentum {beta}* correction performed in a dedicated beam experiment in the 2012 RHIC 250 GeV polarized proton run are presented.
Date: May 20, 2012
Creator: Y., Luo; Bai, M.; Fischer, W.; Marusic, A.; Mernick, K. & White, S.
Partner: UNT Libraries Government Documents Department

Near real-time response matrix calibration for 10 Hz GOFB

Description: The 10 Hz global orbit feedback (GOFB), for damping the trajectory perturbation ({approx}10 Hz) due to the vibrations of the triplet quadrupoles, is operational. The correction algorithm uses transfer functions between the beam position monitors and correctors obtained from the online optics model and a correction algorithm based on singular value decomposition (SVD). Recently the calibration of the transfer functions was measured using beam position measurements acquired while modulating dedicated correctors. In this report, the feedback results with model matrix and measured matrix are compared.
Date: May 20, 2012
Creator: C., Liu; Hulsart, R.; Marusic, A.; Mernick, K.; Michnoff, R. & Minty, M.
Partner: UNT Libraries Government Documents Department

Improvements for operational baseband tune and coupling measurements and feedback at RHIC

Description: Throughout RHIC Run-9 (polarized protons) and Run-10 (gold), numerous modifications to the Baseband Tune (BBQ) system were made. Hardware and software improvements resulted in improved resolution and control, allowing the system to overcome challenges from competing 60Hz mains harmonics, other spectral content, and other beam issues. Test points from the Analog Front End (AFE) were added and connected to diagnostics that allow us to view signals, such as frequency spectra on a Sr785 dynamic signal analyser (DSA), in real time. Also, additional data can now be logged using a National Instruments DAQ (NI-DAQ). Development time using tune feedback to obtain full-energy beams at RHIC has been significantly reduced from many ramps over a few weeks, to just a few ramps over several hours. For many years BBQ was an expert-only system, but the many improvements allowed BBQ to finally be handed over to the Operations Staff for routine control.
Date: May 2, 2010
Creator: Wilinski, M.; Dawson, C.; Degen, C.; Marusic, A.; Mernick, K.; Minty, M. et al.
Partner: UNT Libraries Government Documents Department

Microwave link phase compensation for longitudinal stochastic cooling in RHIC

Description: A new microwave link has been developed for the longitudinal stochastic cooling system, replacing the fiberoptic link used for the transmission of the beam signal from the pickup to the kicker. This new link reduces the pickup to kicker delay from 2/3 of a turn to 1/6 of a turn, which greatly improves the phase margin of the system and allows operation at higher frequencies. The microwave link also introduces phase modulation on the transmitted signal due to variations in the local oscillators and time of flight. A phase locked loop tracks a pilot tone generated at a frequency outside the bandwidth of the cooling system. Information from the PLL is used to calculate real-time corrections to the cooling system at a 10 kHz rate. The design of the pilot tone system is discussed and results from commissioning are described.
Date: May 2, 2010
Creator: Mernick, K.; Blaskiewicz, M.; Brennan, J.M.; Johnson, B. & Severino, F.
Partner: UNT Libraries Government Documents Department

RHIC spin flipper AC dipole controller

Description: The RHIC Spin Flipper's five high-Q AC dipoles which are driven by a swept frequency waveform require precise control of phase and amplitude during the sweep. This control is achieved using FPGA based feedback controllers. Multiple feedback loops are used to and dynamically tune the magnets. The current implementation and results will be presented. Work on a new spin flipper for RHIC (Relativistic Heavy Ion Collider) incorporating multiple dynamically tuned high-Q AC-dipoles has been developed for RHIC spin-physics experiments. A spin flipper is needed to cancel systematic errors by reversing the spin direction of the two colliding beams multiple times during a store. The spin flipper system consists of four DC-dipole magnets (spin rotators) and five AC-dipole magnets. Multiple AC-dipoles are needed to localize the driven coherent betatron oscillation inside the spin flipper. Operationally the AC-dipoles form two swept frequency bumps that minimize the effect of the AC-dipole dipoles outside of the spin flipper. Both AC bumps operate at the same frequency, but are phase shifted from each other. The AC-dipoles therefore require precise control over amplitude and phase making the implementation of the AC-dipole controller the central challenge.
Date: March 28, 2011
Creator: Oddo, P.; Bai, M.; Dawson, C.; Gassner, D.; Harvey, M.; Hayes, T. et al.
Partner: UNT Libraries Government Documents Department

Conceptual design of a high precision dual directional beam position monitoring system for beam crosstalk cancellation and improved output pulse shapes

Description: The Relativistic Heavy Ions Collider (RHIC) would benefit from improved beam position measurements near the interaction points that see both beams, especially as the tolerances become tighter when reducing the beam sizes to obtain increased luminosity. Two limitations of the present beam position monitors (BPMs) would be mitigated if the proposed approach is successful. The small but unavoidable cross-talk between signals from bunches traveling in opposite directions when using conventional BPMs will be reduced by adopting directional BPMs. Further improvements will be achieved by cancelling residual cross-talk using pairs of such BPMs. Appropriately delayed addition and integration of the signals will also provide pulses with relatively flat maxima that will be easier to digitize by relaxing the presently very stringent timing requirements.
Date: April 15, 2012
Creator: P., Thieberger; Dawson, C.; Fischer, W.; Gassner, D.; Hulsart, R.; Mernick, K. et al.
Partner: UNT Libraries Government Documents Department

Dynamically tuned high-Q AC-dipole implementation

Description: AC-dipole magnets are typically implemented as a parallel LC resonant circuit. To maximize efficiency, it's beneficial to operate at a high Q. This, however, limits the magnet to a narrow frequency range. Current designs therefore operate at a low Q to provide a wider bandwidth at the cost of efficiency. Dynamically tuning a high Q resonant circuit tries to maintain a high efficiency while providing a wide frequency range. The results of ongoing efforts at BNL to implement dynamically tuned high-Q AC dipoles will be presented.
Date: May 2, 2010
Creator: Oddo, P.; Bai, M.; Dawson, W.C.; Meng, W.; Mernick, K.; Pai, C. et al.
Partner: UNT Libraries Government Documents Department

The dipole corrector magnets for the RHIC fast global orbit feedback system

Description: The recently completed RHIC fast global orbit feedback system uses 24 small 'window-frame' horizontal dipole correctors. Space limitations dictated a very compact design. The magnetic design and modelling of these laminated yoke magnets is described as well as the mechanical implementation, coil winding, vacuum impregnation, etc. Test procedures to determine the field quality and frequency response are described. The results of these measurements are presented and discussed. A small fringe field from each magnet, overlapping the opposite RHIC ring, is compensated by a correction winding placed on the opposite ring's magnet and connected in series with the main winding of the first one. Results from measurements of this compensation scheme are shown and discussed.
Date: March 28, 2011
Creator: Thieberger, P.; Arnold, L.; Folz, C.; Hulsart, R.; Jain, A.; Karl, R. et al.
Partner: UNT Libraries Government Documents Department

High Precision Tune and Coupling Feedback and Beam Transfer Function Measurements in RHIC

Description: Precision measurement and control of the betatron tunes and betatron coupling in the Relativistic Heavy Ion Collider (RHIC) are required for establishing and maintaining both good operating conditions and, particularly during the ramp to high beam energies, high proton beam polarization. While the proof-of-principle for simultaneous tune and coupling feedback was successfully demonstrated earlier, routine application of these systems has only become possible recently. Following numerous modifications for improved measurement resolution and feedback control, the time required to establish full-energy beams with the betatron tunes and coupling regulated by feedback was reduced from several weeks to a few hours. A summary of these improvements, select measurements benefitting from the improved resolution and a review of system performance are the subject of this report.
Date: May 23, 2010
Creator: Minty, M.; Curcio, A.; Dawson, C.; Degen, C.; Luo, Y.; Marr, G. et al.
Partner: UNT Libraries Government Documents Department

High precision tune and coupling measurements and tune/coupling feedback in RHIC

Description: Precision measurement and control of the betatron tunes and betatron coupling in RHIC are required for establishing and maintaining both good operating conditions and, particularly during the ramp to high beam energies, high proton beam polarization. While the proof-of-principle for simultaneous tune and coupling feedback was successfully demonstrated earlier, routine application of these systems has only become possible recently. Following numerous modifications for improved measurement resolution and feedback control, the time required to establish full-energy beams with the betatron tunes and coupling regulated by feedback was reduced from several weeks to a few hours. A summary of these improvements, select measurements benefitting from the improved resolution and a review of system performance are the subject of this report.
Date: August 1, 2010
Creator: Minty, M.; Curcio, A.; Dawson, C.; Degen, C.; Luo, Y.; Marr, G. et al.
Partner: UNT Libraries Government Documents Department

Analysis of kicker noise induced beam emittance growth

Description: Over the last few years, physicists have occasionally observed the presence of noise acting on the RHIC beams leading to emittance growth at high beam energies. While the noise was sporadic in the past, it became persistent during the Run-11 setup period. An investigation diagnosed the source as originating from the RHIC dump kicker system. Once identified the issue was quickly resolved. We report in this paper the investigation result, circuit analysis, measured and simulated waveforms, solutions, and future plans.
Date: May 20, 2012
Creator: W., Zhang; Sandberg, J.; Ahrens, L.; Blacker, I.M.; Brennan, M.; Blaskiewicz, M. et al.
Partner: UNT Libraries Government Documents Department

Beam experiments towards high-intensity beams in RHIC

Description: Proton bunch intensities in RHIC are planned to be increased from 2 {center_dot} 10{sup 11} to 3 {center_dot} 10{sup 11} protons per bunch to increase the luminosity, together with head-on beam-beam compensation using electron lenses. To study the feasibility of the intensity increase, beam experiments are being performed. Recent experimental results are presented.
Date: May 20, 2012
Creator: C., Montag; Ahrens, L.; Brennan, J.M.; Blaskiewicz, M.; Drees, A.; Fischer, W. et al.
Partner: UNT Libraries Government Documents Department

RHIC 10 Hz global orbit feedback system

Description: Vibrations of the cryogenic triplet magnets at the Relativistic Heavy Ion Collider (RHIC) are suspected to be causing the horizontal beam perturbations observed at frequencies around 10 Hz. Several solutions to counteract the effect have been considered in the past, including a local beam feedback system at each of the two experimental areas, reinforcing the magnet base support assembly, and a mechanical servo feedback system. However, the local feedback system was insufficient because perturbation amplitudes outside the experimental areas were still problematic, and the mechanical solutions are very expensive. A global 10 Hz orbit feedback system consisting of 36 beam position monitors (BPMs) and 12 small dedicated dipole corrector magnets in each of the two 3.8 km circumference counter-rotating rings has been developed and commissioned in February 2011. A description of the system architecture and results with beam will be discussed.
Date: March 28, 2011
Creator: Michnoff, R.; Arnold, L.; Carboni, L.; Cerniglia, P; Curcio, A.; DeSanto, L. et al.
Partner: UNT Libraries Government Documents Department