SLAC, Menlo Park, California
The Cornell Electron Storage Ring (CESR) has been reconfigured as an ultra low emittance damping ring for use as a test accelerator (CesrTA) for International Linear Collider (ILC) damping ring R&D. One of the primary goals of the CesrTA program are to investigate the interaction of the electron cloud with low emittance positron beam, to explore methods to suppress the electron cloud, and to develop suitable advanced instrumentation required for these experimental studies. This paper report the simulation of the electron-cloud formation in the wiggler and quadrupole magnets using 3D code CLOUDLAND. The transverse distribution of electron cloud in a wiggler magnet is similar to a dipole magnet except in the zero vertical field regions where the electrons have complicated trajectories and therefore a longer lifetime. Fortunately, these electrons are dominantly direct-photo-electrons and can be easily reduced by properly arranging photon absorbers. Simulations show that the electron cloud in a quadrupole magnet can be trapped for long time due to the mirror field effect.
CLASSE, Ithaca, New York
CERN, Geneva
ANL, Argonne
KEK, Ibaraki
SLAC, Menlo Park, California
Over the course of the CesrTA program, the Cornell Electron Storage Ring (CESR) has been instrumented with several retarding field analyzers (RFAs), which measure the local density and energy distribution of the electron cloud. These RFAs have been installed in drifts, dipoles, quadrupoles, and wigglers; and data have been taken in a variety of beam conditions and bunch configurations. This paper will provide an overview of these results, and give a preliminary evaluation of the efficacy of cloud mitigation techniques implemented in the instrumented vacuum chambers.
INFN/LNF, Frascati (Roma)
SLAC, Menlo Park, California
Some collective effects have been studied for the SuperB* high luminosity collider. Estimates of the effect of Intra Beam Scattering on the emittance and energy spread growths have been carried up for both the High Energy (HER, positrons) and the Low Energy (LER, electrons) rings. Electron cloud build up simulations for HER were performed with the ECLOUD code, developed at CERN**, to predict the cloud formation in the arcs, taking into account possible remediation techniques such as clearing electrodes. The new code CMAD, developed at SLAC***, has been used to study the effect of this electron cloud on the beam and assess the thresholds above which the electron cloud instability would set in.
* M. E. Biagini, proceedings of PAC'09.
** F. Zimmermann, CERN, LHC-Project-Report-95, 1997.
*** M. Pivi, proceedings of PAC'09.
KEK, Ibaraki
SLAC, Menlo Park, California
Grooved surfaces are effective to suppress the secondary electron emission, and can be a possible technique to mitigate the electron cloud instability (ECI) in positron/proton storage rings. Various types of triangular grooved surfaces have been studied in a laboratory, and also using an intense positron beam of the KEKB B-factory. The grooves have vertex angles of 20 ~ 30 degrees, and depths of 2.5 mm. In the laboratory, the secondary electron yield (SEY) of sample pieces were measured using an electron beam in a magnetic-free condition. The maximum SEY well below 1.0 was obtained after some extent of electron bombardment for most of grooved surfaces. To test he groove efficacy in magnetic field regions of particle accelerators, insertions with several types of grooved surfaces were installed into a test chamber in a wiggler magnet of KEKB positron ring. In a dipole-like chamber wit magnetic field (0.78 T), the reduction in the electron density around the beam was observed for a grooved section when compared to the case of a flat surface with TiN coating. An R&D effort is underway to optimize and manufacture the grooved surface in accelerator beam pipes for practical use.
KEK, Ibaraki
SLAC, Menlo Park, California
In order to mitigate the electron cloud instability (ECI) in a positron ring, an electron clearing electrode with a very thin structure has been developed. The electrode has been tested with an intense positron beam of the KEKB B-factory using a test chamber. A drastic reduction in the electron density around the beam was demonstrated in a dipole magnetic field (0.78 T). The clearing electrode was then applied to the actual copper beam pipe (94 mm in diameter) with antechambers for wiggler magnets of KEKB. The feed-through was revised to improve reliability, and the length was modified to fit a real magnet. The input power into the electrode was estimated to be approximately 80 W/m. The clear reduction in the electron density was also observed by applying a voltage of +500 V to the electrode. The design of clearing electrodes has now reached a high reliability and it is suitable for accelerator applications.
CLASSE, Ithaca, New York
CERN, Geneva
Carleton University, College of Natural Sciences, Ottawa, Ontario
Purdue University, West Lafayette, Indiana
LBNL, Berkeley, California
Grove City College, Grove City, Pennsylvania
INFN/LNF, Frascati (Roma)
ASCo, Clayton, Victoria
KEK, Ibaraki
Clarkson University, Potsdam, New York
BNL, Upton, Long Island, New York
ANL, Argonne
CalPoly, San Luis Obispo, CA
Cockcroft Institute, Warrington, Cheshire
SLAC, Menlo Park, California
Fermilab, Batavia
Technion, Haifa
Loyola University, Chicago, Illinois
The Cornell Electron Storage Ring (CESR) has been reconfigured as a test accelerator (CesrTA) for a program of electron cloud (EC) research at ultra low emittance. The instrumentation in the ring has been upgraded with local diagnostics for measurement of cloud density and with improved beam diagnostics for the characterization of both the low emittance performance and the beam dynamics of high intensity bunch trains interacting with the cloud. Finally a range of EC mitigation methods have been deployed and tested. Measurements of cloud density and its impact on the beam under a range of conditions will be presented and compared with simulations. The effectiveness of a range of mitigation techniques will also be discussed.
INFN/LNF, Frascati (Roma)
LPSC, Grenoble
SLAC, Menlo Park, California
CERN, Geneva
IN2P3-LAPP, Annecy-le-Vieux
LAL, Orsay
INFN-Pisa, Pisa
CEA, Gif-sur-Yvette
IN2P3 IPNL, Villeurbanne
BINP SB RAS, Novosibirsk
University of Pisa and INFN, Pisa
The SuperB project is an international effort aiming at building in Italy a very high luminosity e+e- (1036 cm-2 sec-1) asymmetric collider at the B mesons cm energy. The accelerator design has been extensively studied and changed during the past year. The present design, - based on the new collision scheme, with large Piwinski angle and the use of 'crab' sextupoles, which has been successfully tested at the DAPHNE Phi-Factory at LNF Frascati, - provides larger flexibility, better dynamic aperture and in the Low Energy Ring spin manipulation sections, needed for having longitudinal polarization of the electron beam at the Interaction Point. The Interaction Region has been further optimized in terms of apertures and reduced backgrounds in the detector. The injector complex design has been also updated. A summary of the design status, including details on lattice and spin manipulation will be presented in this paper.
CLASSE, Ithaca, New York
LBNL, Berkeley, California
ANL, Argonne
CalPoly, San Luis Obispo, CA
SLAC, Menlo Park, California
The Cornell Electron Storage Ring Test Accelerator (CesrTA) program has included extensive measurements of coherent tune shifts for a variety of electron and positron beam energies, bunch current levels, and bunch train configurations. The tune shifts have been shown to result primarily from the interaction of the beam with the space-charge field of the beam-induced low-energy electron cloud in the vacuum chamber. Comparison to several advanced electron cloud simulation program packages has allowed determination of the sensitivity of these measurements to physical parameters such as the synchrotron radiation flux, its interaction with the vacuum chamber wall, the beam emittance and lattice optics, as well as to those of the various contributions to the electron secondary yield model. We report on progress in understanding the cloud buildup and decay mechanisms in magnetic fields and in field-free regions, addressing quantitatively the precise determination of the physical parameters of the modelling. Validation of these models will serve as essential input in the design of damping rings for future high-energy linear colliders.
SLAC, Menlo Park, California
LBNL, Berkeley, California
CLASSE, Ithaca, New York
INFN/LNF, Frascati (Roma)
ANL, Argonne
Cockcroft Institute, Warrington, Cheshire
KEK, Ibaraki
CERN, Geneva
As part of the International Linear Collider (ILC) collaboration, we have compared the electron cloud effect for different Damping Ring designs respectively with 6.4 km and 3.2 km circumference and investigated the feasibility of a shorter damping ring with respect to the electron cloud build-up and related beam instability. These studies 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 and would allow to considerably reduce the number of components, wiggler magnets and costs. We also briefly discuss the plans for future studies including the luminosity upgrade option with shorter bunch spacing, the evaluation of mitigations and the integration of the CesrTA results into the Damping Ring design.