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Simulations and Experiments of Beam-Beam Effects in e+e- Storage Rings

Description: Over the past decade, extensive simulations of beam-beam effects in e{sup +}e{sup -} colliders, based on the particle-in-cell method, were developed to explain many complex experimental observations. Recently, such simulations were used to predict the future luminosity performance of e{sup +}e{sup -} colliders. Some predictions have been proven to be correct in the existing accelerators. In this paper, many effects such as the beam-beam limit, crossing angle, parasitic collisions, betatron spectrum, and the beam-beam lifetime, will be directly compared between simulations and experiments.
Date: May 16, 2005
Creator: Cai, Y.; Seeman, J.; /SLAC; Kozanecki, W.; /DAPNIA, Saclay; Ohmi, K. et al.
Partner: UNT Libraries Government Documents Department

Simulation of the Electron Cloud for Various Configurations of a Damping Ring for the ILC

Description: In the beam pipe of the positron damping ring of the International Linear Collider (ILC), an electron cloud may be first produced by photoelectrons and ionization of residual gases and then increased by the secondary emission process. This paper reports the assessment of electron cloud effects in a number of configuration options for the ILC baseline configuration. Careful estimates were made of the secondary electron yield threshold for electron cloud build-up, and the related single- and coupled-bunch instabilities, as a function of beam current and surface properties for a variety of optics designs. When the configuration for the ILC damping rings was chosen at the end of 2005, the results from these studies were important considerations. On the basis of the theoretical and experimental work, the baseline configuration currently specifies a pair of 6 km damping rings for the positron beam, to mitigate the effects of the electron cloud that could present difficulties in a single 6 km ring.
Date: June 23, 2006
Creator: Pivi, M.; Wang, L.; /SLAC; Ohmi, K.; /KEK, Tsukuba; Wanzenberg, R. et al.
Partner: UNT Libraries Government Documents Department

Potential-Well Distortion, Microwave Instability, and Their Effects with Colliding Beams at KEKB

Description: Microwave instability in the Low Energy Ring of KEKB was studied using a broadband impedance model. The model gave excellent descriptions of longitudinal dynamics for both positive and negative momentum compactions. Moreover, it predicted that the threshold of microwave instability was a factor of two lower than the machine nominal operating bunch current. The prediction was confirmed by a measurement using the Belle detector. Furthermore, we integrated the longitudinal wakefield into the beam-beam simulation and applied it to study the combined effects in KEKB. As a result, the beam-beam simulation became truly three-dimensional with emittance growth in all three dimensions simultaneously as the beam currents increase. In addition, an observed mystery of asymmetry in the horizontal scan could also be explained by our simulations.
Date: April 1, 2009
Creator: Cai, Yunhai; /SLAC; Flanagan, J.; Fukuma, H.; Funakoshi, Y.; Ieiri, T. et al.
Partner: UNT Libraries Government Documents Department

Measurements, Analysis, and Simulation of Microwave Instability in the Low Energy Ring of KEKB

Description: Using a streak camera, we measured the longitudinal profiles of a positron bunch in the Low Energy Ring (LER) of KEKB at various currents. The measured charge densities were used to construct a simple Q=1 broadband impedance model. The model, with three parameters, not only gave an excellent description of longitudinal dynamics for positive momentum compaction factor but also for the negative ones, including bunch shortening below a threshold and bursting modes above the threshold. Furthermore, our study indicated that the threshold of microwave instability was about 0.5 mA in bunch current in the LER. At the nominal operating current 1.0 mA, there was a 20% increase of the energy spread. The results of measurement, analysis, and simulations will be presented in this paper.
Date: May 7, 2009
Creator: Cai, Yunhai; /SLAC; Flanagan, J.; Fukuma, H.; Funakoshi, Y.; Ieiri, T. et al.
Partner: UNT Libraries Government Documents Department

Electron Cloud Build-up Study for DAFNE

Description: After the first experimental observations compatible with the presence of the e-cloud effect in the DAFNE positron ring, a more systematic study has been performed regarding the e-cloud build-up. The measured field map of the magnetic field has been taken into account in the simulation for elements present in the four 10 m long bending sections, representing 40% of the whole positron ring. The obtained simulation results are presented together with the recent experimental observations performed on the vacuum behavior of the positron ring.
Date: May 27, 2005
Creator: Vaccarezza, C.; Cimino, R.; Drago, A.; Zobov, M.; Bellodi, G.; Schulte, D. et al.
Partner: UNT Libraries Government Documents Department

Modeling Incoherent Electron Cloud Effects

Description: Incoherent electron effects could seriously limit the beam lifetime in proton or ion storage rings, such as LHC, SPS, or RHIC, or blow up the vertical emittance of positron beams, e.g., at the B factories or in linear-collider damping rings. Different approaches to modeling these effects each have their own merits and drawbacks. We describe several simulation codes which simplify the descriptions of the beam-electron interaction and of the accelerator structure in various different ways, and present results for a toy model of the SPS. In addition, we present evidence that for positron beams the interplay of incoherent electron-cloud effects and synchrotron radiation can lead to a significant increase in vertical equilibrium emittance. The magnitude of a few incoherent e+e- scattering processes is also estimated. Options for future code development are reviewed.
Date: June 18, 2007
Creator: Vay, Jean-Luc; Benedetto, E.; Fischer, W.; Franchetti, G.; Ohmi, K.; Schulte, D. et al.
Partner: UNT Libraries Government Documents Department

Summary of the LARP Mini-Workshop on Beam-Beam Compensation 2007

Description: The LARP Mini-Workshop on Beam-Beam Compensation 2007 was held at SLAC, 2-4 July 2007. It was attended by 33 participants from 10 institutions in Asia, Europe, and America. 26 presentations were given, while more than one third of the time was allocated to discussions. The workshop web site is Ref. [1]. The workshop's main focus was on long-range and head-on beam-beam compensation, with a view towards application in the LHC. Other topics included the beam-beam performance of previous, existing and future circular colliders; beam-beam simulations; new operating modes, theory, and unexplained phenomena. This summary is also published as Ref. [2].
Date: November 7, 2011
Creator: Fischer, Wolfram; /Brookhaven; Bruning, Oliver S.; Koutchouk, J.P.; Zimmermann, F.; /CERN et al.
Partner: UNT Libraries Government Documents Department

Recommendation for Mitigations of the Electron Cloud Instability in the ILC

Description: Electron cloud has been identified as one of the highest priority issues for the international Linear Collider (ILC) Damping Rings (DR). An electron cloud Working Group (WG) has evaluated the electron cloud effect and instability, and mitigation solutions for the electron cloud formation. Working group deliverables include recommendations for the baseline and alternate solutions to the electron cloud formation in various regions of the ILC Positron DR, which is presently assumed to be the 3.2 km design. Detailed studies of a range of mitigation options including coatings, clearing electrodes, grooves and novel concepts, were carried out over the previous several years by nearly 50 researchers, and the results of the studies form the basis for the recommendation. The recommendations are the result of the working group discussions held at numerous meetings and during a dedicated workshop. In addition, a number of items requiring further investigation were identified during the discussions at the Cornell meeting and studies will be carried out at CesrTA, a test accelerator dedicated to electron cloud studies, and other institutions.
Date: December 13, 2011
Creator: Pivi, M. T. F.; Wang, L.; Demma, T.; Guiducci, S.; Suetsugu, Y.; Shibata, K. et al.
Partner: UNT Libraries Government Documents Department

Study of the beam-beam limit in e{sup +}e{sup -} circular colliders

Description: Beam-beam effects limit the luminosity of circular colliders. Once the bunch population exceeds a threshold, the luminosity increases at a slower rate. This phenomenon is called the beam-beam limit. Onset of the beam-beam limit has been analyzed with various simulation methods based on the weak-strong and strong-strong models. We have observed that an incoherent phenomenon is mainly concerned in the beam-beam limit. The simulation have shown that equilibrium distributions of the two colliding beams are distorted from Gaussians when the luminosity is limited. The beam-beam limit is estimated to be (xi) {approx} 0.1 for a B factory with damping time of several thousand turns.
Date: April 2, 2004
Creator: Ohmi, K.; Tawada, M.; Cai, Y.; Kamada, S.; Oide, K. & Qiang, J.
Partner: UNT Libraries Government Documents Department

Recommendation for Mitigations of the Electron Cloud Instability in the ILC

Description: Electron cloud has been identified as one of the highest priority issues for the international Linear Collider (ILC) Damping Rings (DR). An electron cloud Working Group (WG) has evaluated the electron cloud effect and instability, and mitigation solutions for the electron cloud formation. Working group deliverables include recommendations for the baseline and alternate solutions to the electron cloud formation in various regions of the ILC Positron DR, which is presently assumed to be the 3.2 km design. Detailed studies of a range of mitigation options including coatings, clearing electrodes, grooves and novel concepts, were carried out over the previous several years by nearly 50 researchers, and the results of the studies form the basis for the recommendation. The recommendations are the result of the working group discussions held at numerous meetings and during a dedicated workshop. In addition, a number of items requiring further investigation were identified during the discussions at the Cornell meeting and studies will be carried out at CesrTA, a test accelerator dedicated to electron cloud studies, and other institutions.
Date: September 4, 2011
Creator: Pivi, M. T. F.; Wang, L.; Demma, T.; Guiducci, S.; Suetsugu, Y.; Shibata, K. et al.
Partner: UNT Libraries Government Documents Department

Accelerator Physics Code Web Repository

Description: In the framework of the CARE HHH European Network, we have developed a web-based dynamic accelerator-physics code repository. We describe the design, structure and contents of this repository, illustrate its usage, and discuss our future plans, with emphasis on code benchmarking.
Date: October 24, 2006
Creator: Zimmermann, F.; Basset, R.; Bellodi, G.; Benedetto, E.; Dorda, U.; Giovannozzi, M. et al.
Partner: UNT Libraries Government Documents Department

Recommendation for the Feasibility of more Compact LC Damping Rings

Description: As part of the international Linear Collider (ILC) collaboration, we have compared the electron cloud (EC) effect for different Damping Ring (DR) designs respectively with 6.4 km and 3.2 km circumference and investigated the feasibility of the shorter damping ring with respect to the electron cloud build-up and related beam instabilities. The studies for a 3.2 km ring were carried out with beam parameters of the ILC Low Power option. A reduced damping ring circumference has been proposed for the new ILC baseline design SB2009 [1] and would allow considerable reduction of the number of components, wiggler magnets and costs. We discuss the impact of the proposed operation of the ILC at high repetition rate 10 Hz and address the necessary modifications for the DRs. We also briefly discuss the plans for future studies including the luminosity upgrade option with shorter bunch spacing, the evaluation of mitigation techniques and the integration of the CesrTA results into the Damping Ring design.
Date: June 15, 2010
Creator: Pivi, M.T.F.; Wang, L.; /SLAC; Demma, T.; Guiducci, S.; /Frascati et al.
Partner: UNT Libraries Government Documents Department