A Study of the Effect of Beam-Beam Interactions on CESR Optics
The CESR storage ring facility has begun operation in an energy region which allows high-statistics investigation of charm-quark bound states. Experience during the first two years has shown that the effects of parasitic crossings in the pretzel orbits present an important factor in injection efficiency, in the beam lifetime and in the stored current limits. We compare the results of beam dynamics and tracking calculations which quantify the effects of these parasitic crossings on optics and dynamic aperture for the injected and stored trajectories to observations of beam behavior.
Study of turn-by-turn vertical beam dynamics at low and high energy cesr operation
Presently, the Cornell Electron-Positron Storage Ring (CESR) is operated at two different beam energies: low energy (E=2GeV) for high energy physics (CESR-c), and high energy (E=5.3GeV) for synchrotron radiation production for the Cornell High Energy Synchrotron Source (CHESS). The electron and positron bunches' vertical dynamics at these two energies are vastly different, in part due to the change in the pretzel orbit, the presence of wiggler magnets at low energy, and synchrotron radiation power at two different energies. Using a 32 channel photomultiplier array and a beam position monitor (BPM), vertical beam dynamics were measured on a turn-by-turn basis during CHESS and CESR-c operation as well as dedicated machine studies time. For these studies, electron cloud effects such as vertical tune shift and vertical beam size blow-up along the electron and positron trains are quantified at these two vastly different beam energies.
The Unusual Variability of the Large Magellanic Cloud Planetary Nebula RPJ 053059–683542
We present images and light curves of the bipolar planetary nebula RPJ 053059-683542 that was discovered in the Reid-Parker AAO UKST Hα survey of the Large Magellanic Cloud. The emission from this object appears entirely nebular, with the central star apparently obscured by a central band of absorption that bisects the nebula. The light curves, which were derived from images from the SuperMACHO project at CTIO, showed significant, spatially resolved variability over the period 2002 January through 2005 December. Remarkably, the emission from the two bright lobes of the nebula vary either independently or similarly but with a phase lag of at least 1 yr. The optical spectra show a low level of nebular excitation, and only modest N enrichment. Infrared photometry from the 2MASS and SAGE surveys indicates the presence of a significant quantity of dust. The available data imply that the central star has a close binary companion and that the system has undergone some kind of outburst event that caused the nebular emission to first brighten and then fade. Further monitoring, high-resolution imaging, and detailed IR polarimetry and spectroscopy would uncover the nature of this nebula and the unseen ionizing source.