INFN/LNF, Frascati (Roma), Italy
CLASSE, Ithaca, New York, USA
IHEP Beijing, Beijing, People's Republic of China
SLAC, Menlo Park, California, USA
KEK, Ibaraki, Japan
CLASSE, Ithaca, New York, USA
CMU, Pittsburgh, Pennsylvania, USA
KEK, Ibaraki, Japan
CalPoly, San Luis Obispo, California, USA
The study of electron cloud-related instabilities for the CESR-TA project permits the observation of the interaction of the electron cloud with the stored beam under a variety of accelerator conditions. These measurements are undertaken utilizing automatic and semi-automatic techniques for three basic observations: the measurement of tune shifts of individual bunches along a train, the detection of the coherent self-excited spectrum for each bunch within a train and the pulsed excitation of either the betatron dipole or head-tail mode for each individual bunch within the train, followed by the observation of the damping of its coherent motion. These techniques are employed to study the electron cloud-related interactions in a number of conditions, such as trains of bunches with low emittance and spaced by as little as 4 nsec between bunches. We report on the most recent observations and results.
CLASSE, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
SLAC, Menlo Park, California, USA
Work supported by US Department of Energy grant number DE-FC02-08ER41538
and the National Science Foundation grant number PHY-0734867
SLAC, Menlo Park, California, USA
ANL, Argonne, USA
CLASSE, Ithaca, New York, USA
INFN/LNF, Frascati (Roma), Italy
LBNL, Berkeley, California, USA
KEK, Ibaraki, Japan
Chalmers University of Technology, Chalmers Tekniska Högskola, Gothenburg, Sweden
Electron cloud has been identified as one of the highest priority issues for the ILC Damping Rings (DR). A working group 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 for the electron cloud mitigation in various regions of the ILC Positron DR, which is presently assumed to be the 3.2km 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 assessments of the benefits or risks associated with the various options were based on a systematic ranking scheme. The recommendations are the result of the working group discussions held at numerous meetings and during a dedicated workshop. The mitigation choices will be also presented in a more detailed report later in 2012. In addition, a number of items requiring further investigation were identified and studies will be carried out at CesrTA and other institutions.
CLASSE, Ithaca, New York, USA
CMU, Pittsburgh, Pennsylvania, USA
LBNL, Berkeley, California, USA
Harvard University, Cambridge, Massachusetts, USA
The Cornell Electron Storage Ring has been reconfigured as a test accelerator (CesrTA). Measurements of electron cloud densities have been made at CesrTA using the TE Wave transmission technique. However, interpretation of the data based on single pass transmission is problematic because of the reflections and standing waves produced by discontinuities in the beam pipe - from pumps, bellows, etc. that are normally present in an accelerator vacuum chamber. An alternative model is that of a resonant cavity, formed by the beampipe and its discontinuities. The theory for the measurement of plasma densities in cavities is well established. This paper will apply this theory to electron cloud measurements, present some simplified measurements on waveguide, and apply this model to the interpretation of some of the data taken at CesrTA.
CLASSE, Ithaca, New York, USA
Syracuse University, Syracuse, USA
CERN, Geneva, Switzerland
KEK, Ibaraki, Japan
The Cornell Electron Storage Ring Test Accelerator program includes investigations into the mitigation of electron cloud buildup using a variety of techniques in custom vacuum chambers. The CESR ring accommodates two such chambers equipped with BPM-style pickup detectors shielded against the direct beam-induced signal. The signals provide time-resolved information on cloud development. Results for diamond-like carbon, amorphous carbon, and TiN coatings have been compared to those for an uncoated aluminum chamber. Here we report on extensions to the ECLOUD modeling code which refine its description of a variety of new types of in situ vacuum chamber comparisons. Our results highlight the sensitivity afforded by these measurements to the modeled photoelectron production and secondary yield parameters. We draw conclusions comparing the photoelectron and secondary yield properties of the various vacuum chamber coatings, including conditioning effects as a function of synchrotron radiation dose. We find substantial conditioning effects in both the quantum efficiency for producing photoelectrons and in the secondary yield.
CLASSE, Ithaca, New York, USA
CERN, Geneva, Switzerland
KEK, Ibaraki, Japan
SLAC, Menlo Park, California, USA
Over the course of the past three years, the Cornell Electron Storage Ring (CESR) has been reconfigured to serve as a test facility for next generation particle accelerators. A significant part of this program has been the installation of several diagnostic devices to measure and quantify the electron cloud effect, a potential limiting factor in these machines. In particular, more than 30 Retarding Field Analyzers (RFAs) have been installed in CESR. These devices measure the local electron cloud density and energy distribution, and can be used to evaluate the efficacy of different cloud mitigation techniques. This paper will provide an overview of RFA results obtained at CesrTA over the past year, including measurements taken as function of bunch spacing and wiggler magnetic field. Understanding these results provides a great deal of insight into the behavior of the electron cloud.