beam-beam-effects

Paper	Title	Other Keywords	Page
TUPC040	Measurements of Beam-beam Kick using a Gated Beam-position Monitor under Crabbing Collision at KEKB	positron, electron, betatron, luminosity	1143
	T. Ieiri, H. Fukuma, Y. Funakoshi, M. Masuzawa, K. Ohmi, M. Tobiyama KEK, Ibaraki
	KEKB is a double-ring electron/positron collider with a horizontal crossing-angle. The crab cavities installed in 2007 achieved an effective head-on collision and gained a higher specific luminosity. A gated beam-position monitor is a tool to measure the beam-beam effects. A beam-beam kick curve was measured by comparing the beam position between colliding and non-colliding bunches, while shifting the beam orbit at the interaction point (IP). An effective horizontal beam size at the IP was obtained from a linear part of the beam-beam kick around the central orbit. The estimated beam size agreed with a calculated value including the dynamic effects. It was confirmed that the effective horizontal beam size was reduced by the crabbing collision, as expected from a calculation with a rigid Gaussian model. When a horizontal orbit offset was larger than a beam size, however, we found that the measured beam-beam kick curve deviated from calculated values using the Gaussian model. The result suggests that the beam profile might enlarge horizontally in the peripheral part.
WEPP005	Measurements and Effects of the Magnetic Hysteresis on the LHC Crossing Angle and Separation Bumps	simulation, controls, cryogenics, dipole	2530
	N. J. Sammut, H. Burkhardt, C. Giloux, W. Venturini Delsolaro, S. M. White CERN, Geneva N. J. Sammut University of Malta, Faculty of Engineering, Msida
	The superconducting orbit corrector magnets (MCBC and MCBY) in the Large Hadron Collider (LHC) at CERN will be used to generate parallel separation and crossing angles at the interaction points during the different phases that will bring the LHC beams into collision. However, the field errors generated by the inherent hysteresis in the operation region of the orbit correctors may lead to unwanted orbit perturbations that could have a critical effect on luminosity. This paper presents the results obtained from dedicated cryogenic measurements on the orbit correctors from the simulated results on the impact of the hysteresis on the LHC orbit.
WEPP013	Increasing the Integrated Luminosity of SLHC by Levelling via the Crossing Angle	luminosity, simulation, separation-scheme, dipole	2554
	J.-P. Koutchouk, G. Sterbini CERN, Geneva K. Ohmi KEK, Ibaraki
	With an increase of luminosity by a factor of 10, the luminosity lifetime in an upgraded LHC would be limited to a few hours. Furthermore, schemes relying on stronger focusing and reduced beam current increase (which are intrisically less dangerous for machine protection) are penalized by a very short lifetime of around 2 hours. We show in this paper that the "early separation" scheme and/or crab cavities scheme lend themselves to a very efficient luminosity leveling scheme. It allows constant luminosity over many hours as well as a significant increase of integrated luminosity above the performance announced so far. This is achieved by adjusting the crossing angle rather than the beam size by means of a bump closed inside the experimental straight section, i.e. operationally simple. The initially large crossing angle reduces the beam-beam tune shift, allowing an increased beam current and higher performance for lower pile-up in the detector and lower energy deposition in the triplet. The impact of the required large Piwinski angle is investigated.
THYM01	Simulation of Beam-beam Effects and Tevatron Experience	antiproton, proton, emittance, simulation	2937
	A. Valishev Fermilab, Batavia, Illinois
	Simulations of beam-beam effects in the Tevatron correctly describe reality, have predictive power and have been used to support a change in the Tevatron working point to near the half integer. The simulation models and tools are discussed, and comparisons made with observations and measurements.
	Slides
THPC074	Observation of Coherent Oscillations of Colliding Bunches at the Tevatron	proton, antiproton, collider, pick-up	3158
	A. Valishev, V. Kamerdzhiev, V. A. Lebedev Fermilab, Batavia, Illinois F. A. Emanov BINP SB RAS, Novosibirsk
	Commissioning of the new digital tune monitor (DTM) at the Tevatron made it possible to observe vertical dipole oscillations of individual bunches at any time during an HEP store. Since all the bunches have significantly different collision conditions, this device provides vast possibilities for investigation of coherent beam-beam effects. We present theoretical model and experimental observations of coherent beam-beam modes. Analysis of the DTM data and its agreement with theory are discussed.
THPC080	The VEPP-4M Dynamic Aperture Determination with Beam-beam Effects	dynamic-aperture, simulation, collider, insertion	3170
	A. N. Zhuravlev, V. A. Kiselev, E. B. Levichev, O. I. Meshkov, P. A. Piminov, D. N. Shatilov, V. V. Smaluk BINP SB RAS, Novosibirsk
	To determine experimentally the particle stable area under the influence of beam-beam effects in the electron-positron collider VEPP-4M we measure the beam lifetime with high accuracy as a function of moving aperture. The measurement is performed by a photodiode installed in the collider diagnostic beam line. The experimental setup and the measurement results are described. Comparison with the tracking simulation is presented.
THPC081	RF Wire Compensator of Long-range Beam-beam Effects	coupling, emittance, dynamic-aperture, simulation	3173
	U. Dorda, F. Caspers, T. Kroyer, F. Zimmermann CERN, Geneva
	The dynamic aperture of the proton beam circulating in the Large Hadron Collider (LHC) is expected to be limited by up to 120 long-range beam-beam encounters. In order to perfectly compensate the LHC long-range beam-beam effect for nominal as well as for so-called 'PACMAN' bunches, i.e. bunches at the start or end of a bunch train, the wire compensator strength should be adjusted for each bunch individually. Here an RF-based compensator is proposed as a practical solution for the PACMAN compensation. We show that this approach also allows relaxing the power and precision requirements compared with those of a pulsed DC device, to a level within the state-of-the-art of RF technology. Furthermore it allows the use of a passive circulator in the tunnel close to the beam and thus a significantly reduction of the transmission line length and of the resulting multiple reflection issues. Simulations, issues related to RF phase noise and first experimental results from laboratory models as well as from a wire-compensator prototype installed in the CERN Super Proton Synchrotron (SPS) are presented.