SLAC, Menlo Park, California
Funding: Work supported by the Director, Office of Science, High Energy Physics, U.S. DOE under Contract No. DE-AC02-76SF00515.
CMAD is a new code modeling the electron cloud effect driven instability by applying an electron-beam interaction at every element of a beam line, reading a MAD description of the accelerator optics as input. CMAD is parallelized and optimized for speed. It is especially suited for the modeling of incoherent electron-cloud effects for which the spatial distribution of electrons is particularly important. This talk will review the physics, describe the design concept, the present status, benchmarking exercises, and example applications.
LBNL, Berkeley, California
LLNL, Livermore, California
SLAC, Menlo Park, California
Funding: This work was supported by the Office of Science, U. S. Department of Energy, under Contract No. DE-AC02-05CH11231.
A new set of resonances for electron cloud dynamics in the presence of a magnetic field has been found. For short beam bunch lengths and low magnetic fields where lb << 2*π/ωc, (lb = bunch duration, ωc = non-relativistic cyclotron frequency) resonances between the bunch frequency and harmonics of the cyclotron frequency cause an increase in the electron cloud density in narrow ranges of magnetic field near the resonances. For ILC parameters the increase in the density is up to a factor of approximately 3, and the spatial distribution of the electrons is broader near resonances, lacking the well-defined density "stripes" of multipactoring found for non-resonant cases. Simulations with the 2D computer code POSINST, as well as a single-particle tracking code, were used to elucidate the physics of the dynamics. The resonances are expected to affect the electron cloud dynamics in the fringe fields of conventional lattice magnets and in wigglers, where the magnetic fields are low. Results of the simulations, the reason for the bunch-length dependence, and details of the dynamics will be discussed.
C.M. Celata is presently also a visitor in Physics, Mathematics, and Astronomy at California Institute of Technology.
CLASSE, Ithaca, New York
LBNL, Berkeley, California
KEK, Ibaraki
SLAC, Menlo Park, California
Funding: Work supported by the National Science Foundation, the US Department of Energy, and the Japan/US Cooperation Program
Wiggler magnets are one of the key components in the ILC Damping Ring. It is critical to the ILCDR GDE to understand electron cloud (EC) growth and patterns, and to develop EC suppression techniques in the wiggler beampipes. The CESR-c superconducting wigglers, closely matching the parameters of the ILCDR wigglers, serve as unique testing vehicles. As part of the CesrTA project, we replaced the copper beampipes of two SCWs with EC diagnostic beampipes, where one of the beampipes is uncoated and the second is coated with a thin TiN film. Each of the EC diagnostic beampipes is equipped with three retarding field analyzers (RFAs) at strategic longitudinal locations in the wiggler field. Each of the RFAs has 12-fold segmentation to measure the horizontal EC density distribution. To maintain sufficient vertical beam aperture and to fit within the SCW warm bore, a thin style of RFA (with a thickness of 2.5 mm) has been developed and deployed. These SCWs with RFA-equipped beampipe have been installed and successfully operated in the re-configured CesrTA vacuum system. This paper describes the design and the construction of the RFA-equipped SCW beampipes and operational experience.
KEK, Ibaraki
SLAC, Menlo Park, California
Funding: The Japan/US Cooperation Program
Beam instability caused by the electron cloud is expected to be a limiting factor in the performance of future advanced positron and proton storage rings. In a wiggler section of the positron ring of the KEK B-factory (KEKB), we have installed a vacuum chamber with an insertion that can be replaced and including different techniques to study the mitigation of the electron-cloud effect in a high magnetic field region. We have installed an insertion with strip-line clearing electrode, an insertion with triangular grooves and an insertion with a smooth surface, and compared them each other under the same conditions. The electrode insertion is composed of a thin tungsten layer formed on a thin alumina ceramic layer. The groove insertion is composed of TiN-coated triangular grooves running longitudinally. In this paper, we report about the tests in the KEKB and about the large reduction in the measured electron cloud density when the clearing electrode and groove sections are installed with respect to the smooth insertion. These experiments are the first ones demonstrating the principle of the clearing electrode and groove insertions in a magnetic field.
SLAC, Menlo Park, California
LAL, Orsay
The Flight Simulator is a tool used for international collaboration in the writing and deployment of online beam dynamics algorithms. Written as an add-on to the Lucretia tracking software, it allows simulation of a beamline in a control system environment identical to that in the control room. This allows the testing and development of monitoring and correction tools by an international collaboration by making the control system transparent to the user. The native beamline representation are those adopted by Lucretia, so, in order to allow third party software, to interface with this system, it was necessary to develop functionality to convert the lattice to a universal representation. Accelerator Markup Language (AML), and its associated Universal Accelerator Parser (UAP), were used for this purpose. This paper describes the use of the UAP to convert the internal beamline representation to AML, and the testing of this conversion routine using the lattice description of the ATF2 final focus experiment at KEK, Japan. Also described are the inclusion of PLACET and SAD based algorithms using appropriate converters, and tests of these on the ATF2 extraction line.
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.
SLAC, Menlo Park, California
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
JAI, Oxford
KEK, Ibaraki
IHEP Beijing, Beijing
LAL, Orsay
Royal Holloway, University of London, Surrey
IN2P3-LAPP, Annecy-le-Vieux
OXFORDphysics, Oxford, Oxon
ATOMKI, Debrecen
CERN, Geneva
DESY, Hamburg
Fermilab, Batavia
Kyungpook National University, Daegu
PAL, Pohang, Kyungbuk
Kyoto ICR, Uji, Kyoto
ICEPP, Tokyo
University of Tokyo, Tokyo
UCL, London
BNL, Upton, Long Island, New York
Tohoku University, Graduate School of Science, Sendai
UMAN, Manchester
Hiroshima University, Graduate School of Science, Higashi-Hiroshima
Cockcroft Institute, Warrington, Cheshire
ATF2 is a final-focus test beam line that attempts to focus the low-emittance beam from the ATF damping ring to a beam size of about 37 nm, and at the same time to demonstrate nm beam stability, using numerous advanced beam diagnostics and feedback tools. The construction is well advanced and beam commissioning of ATF2 has started in the second half of 2008. ATF2 is constructed and commissioned by ATF international collaborations with strong US, Asian and European participation.
CLASSE, Ithaca, New York
LBNL, Berkeley, California
ANL, Argonne
KEK, Ibaraki
SLAC, Menlo Park, California
Funding: Supported by the US National Science Foundation, the US Department of Energy under Contracts No. DE-AC02-06CH11357, DE-AC02-05CH11231, and DE-AC02-76SF00515, and by the Japan/US Cooperation Program.
CESR at Cornell has been operating as a damping ring test accelerator (CesrTA) with beam parameters approaching those anticipated for the ILC damping rings. A core component of the research program is to fully understand electron cloud effects in CesrTA. As a local probe of the electron cloud, several segmented retarding field analyzers (RFAs) have been installed in CesrTA in dipole, drift and wiggler regions. Using these RFAs, the energy spectrum of the time-average electron cloud current density striking the walls has been measured for a variety of bunch train patterns; with bunch populations up to 2x1010 per bunch, beam energies from 2 to 5 GeV, horizontal geometric emittances from roughly 10 to 133 nm, and bunch lengths of about 1 cm; and for both positron and electron beams. The effect of mitigation measures, such as coatings, has also been studied. This paper will compare these measurements with the predictions of simulation programs, and discuss the implications of these comparisons for our understanding of the physics of electron cloud generation and mitigation in ILC-like damping rings.
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.