KEK, Ibaraki
A few issues on the path of the luminosity upgrade of KEKB B-Factory is described, including coherent synchrotron radiation, design of the interaction region, crab crossing, and high current operation. These issues will raise more obstacles on the upgrade with the High-Current Scheme. As an alternative, {¥it Nano-Beam Scheme} should be considered as a possible option for the upgrade.
INFN/LNF, Frascati (Roma)
SLAC, Menlo Park, California
CERN, Geneva
BINP SB RAS, Novosibirsk
KEK, Ibaraki
University of Pisa and INFN, Pisa
The SuperB project aims at the construction of an asymmetric (4x7 GeV), very high luminosity, B-Factory on the Roma II (Italy) University campus. The luminosity goal of 1036 cm-2 s-1 can be reached with a new collision scheme with large Piwinski angle and the use of “crab” sextupoles. A crab-waist IR has been successfully tested at the DAPHNE Phi-Factory at LNF-Frascati (Italy) in 2008. The crab waist together with very low beta* will allow for operation with relatively low beam currents and reasonable bunch length, comparable to those of PEP-II and KEKB. In the High Energy Ring, two spin rotators permit bringing longitudinally polarized beams into collision at the IP. The lattice has been designed with a very low intrinsic emittance and is quite compact, less than 2 km long. The tight focusing requires a sophisticated Interaction Region with quadrupoles very close to the IP. A Conceptual Design Report was published in March 2007, and beam dynamics and collective effects R&D studies are in progress in order to publish a Technical Design Report by the end of 2010. A status of the design and simulations is presented in this paper.
KEK, Ibaraki
SLAC, Menlo Park, California
It is well known that the beam-beam interaction has a focusing effect and therefore causes a dynamical beating of beta function around the rings. This effect becomes greatly enhanced when a collider, such as KEKB, is operated near half integer. The beating makes it difficult to interpret the measurement of horizontal beam size. We derived two coupled nonlinear equations and solved them analytically to obtain the beam sizes at the interaction points, taking into account of dynamical beta and emittance. It has been demonstrated its effectiveness using actual measured data at the synchrotron light monitors. It is expected that it will be implemented in the control room.
INFN/LNF, Frascati (Roma)
LAL, Orsay
CERN, Geneva
roma3, Rome
Rome University La Sapienza, Roma
BINP SB RAS, Novosibirsk
KEK, Ibaraki
BINP, Novosibirsk
SLAC, Menlo Park, California
INFN-Roma, Roma
In 2007 DAΦNE was upgraded to operate in a regime of large Piwinski angle, with a novel IR optics, reduced vertical beta at the interaction point, and additional sextupoles providing for crab waist collisions. The specific luminosity was boosted by more than a factor of four, and the peak luminosity was more than doubled with respect to the maximum value obtained with the original collider configuration. The DAΦNE commissioning as well as the first experience with large Piwinski angle and crab waist collisions scheme will be reported.
KEK, Ibaraki
Beam-beam tune shift parameter characterizes the strength of the nonlinear interaction due to the beam-beam collision. The tune shift has been measured in many e+e- colliders and has been an indicator for the collider performance. The record for the tune shift is known as 0.07-0.1 depending on the parameter of the collider, especially the radiation damping rate. We discuss the fundamental limit of the tune shift can be very high (>0.2) depending on the choice of collider parameter, which concerns operating point near the half integer tune, head-on collision and travel focus.
BINP SB RAS, Novosibirsk
INFN/LNF, Frascati (Roma)
KEK, Ibaraki
A novel scheme of crab waist collisions has been successfully tested at the electron-positron collider DAΦNE, Italian Phi-factory. In this paper we compare numerical simulations of the crab waist beam-beam interaction with obtained experimental results. For this purpose we perform weak-strong and quasi strong-strong beam-beam simulations using a realistic DAΦNE lattice model that has proven to reproduce reliably both linear and nonlinear collider optics.
KEK, Ibaraki
Crab cavities were installed at KEKB at the beginning of 2007. The beam operation with the crab cavities is in progress. In this paper, machine performance with crab crossing is described focusing on a specific luminosity and a beam lifetime issue related to the dynamic beam-beam effects.
KEK, Ibaraki
The value calculated by using general-purpose computer code SAD for the accelerator is sometimes different from actual measurements. This is because many kinds of factor cause error, like machine error, so we can’t include such error exactly in SAD. Therefore, on the contrary, we consider the model which includes error by using measurement data and derive Hamiltonian from it.
CLASSE, Ithaca, New York
LBNL, Berkeley, California
ANL, Argonne
CalPoly, San Luis Obispo, CA
KEK, Ibaraki
SLAC, Menlo Park, California
Funding: National Science Foundation award 0734867 Office of Science, U.S. Department of Energy contracts DE-AC02-05CH11231 and DE-AC02-06CH11357
The Cornell Electron Storage Ring Test Accelerator (CesrTA) has commenced operation as a linear collider damping ring test bed following its conversion from an e+e- collider in 2008. A core component of the research program is the measurement of effects of synchrotron-radiation-induced electron cloud formation on beam dynamics. We have studied the interaction of the beam with the cloud in a number of experiments, including measurements of coherent tune shifts and emittance growth in various bunch train configurations, with different bunch currents, beam energies, beam emittance, and bunch lengths, for both positron and electron beams. This paper compares these measurements to modeling results from several advanced cloud simulation algorithms and discusses the implications of these comparisons for our understanding of the physics of electron cloud formation and decay in damping rings of the type proposed for future high-energy linear colliders.
KEK, Ibaraki
POSTECH, Pohang, Kyungbuk
Electron cloud causes a transverse single bunch instability above a threshold of the cloud density. The threshold is determeined by the strength of the beam-electron cloud interaction and Landau damping due to the synchrotron oscillation and/or momentum compaction. We discuss that the threshold is remarkably degraded due to the dispersion, one of the parameter of the circular accelerator optics. The single bunch instability is more serious than previous predictions without considering the dispersion, especially in the case that the horizontal beam size due to the dispersion dominates compare than that due to the emittance.
INFN/LNF, Frascati (Roma)
KEK, Ibaraki
Funding: Work supported in part by the “Ministero degli Affari Esteri, Direzione Generale per la Promozione e la Cooperazione Culturale”
A strong horizontal instability has been observed in the DAΦNE positron ring since 2003. Experimental observations suggest an electron cloud induced coupled bunch instability as a possible explanation. In this communication we present a simulation study of the electron cloud coupled bunch instability for the DAΦNE positron ring, performed with the code PEI-M, and compare the numerical results with experimental observations.
SLAC, Menlo Park, California
KEK, Ibaraki
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 a positive momentum compaction factor but also for the negative ones, including bunch shortening bellow a threshold and bursting modes beyond 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.
CLASSE, Ithaca, New York
LBNL, Berkeley, California
KEK, Ibaraki
ANL, Argonne
Fermilab, Batavia
CalPoly, San Luis Obispo, CA
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
SLAC, Menlo Park, California
Cornell University, Ithaca, New York
Cockcroft Institute, Warrington, Cheshire
Funding: Support provided by the US National Science Foundation, the US Department of Energy, and the Japan/US Cooperation Program.
In March of 2008, the Cornell Electron Storage Ring (CESR) concluded twenty eight years of colliding beam operations for the CLEO high energy physics experiment. We have reconfigured CESR as an ultra low emittance damping ring for use as a test accelerator (CesrTA) for International Linear Collider (ILC) damping ring R&D. The primary goals of the CesrTA program are to achieve a beam emittance approaching that of the ILC Damping Rings with a positron beam, to investigate the interaction of the electron cloud with both low emittance positron and electron beams, to explore methods to suppress the electron cloud, and to develop suitable advanced instrumentation required for these experimental studies (in particular a fast x-ray beam size monitor capable of single pass measurements of individual bunches). We report on progress with the CESR conversion activities, the status and schedule for the experimental program, and the first experimental results that have been obtained.