ANL, Argonne
Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
The Advanced Photon Source (APS) is a third-generation storage-ring-based x-ray source that has been operating for more than 11 years and is enjoying a long period of stable, reliable operation. While APS is presently providing state-of-the-art performance to its large user community, we must clearly plan for improvements and upgrades to stay at the forefront scientifically. Significant improvements should be possible through upgrades of beamline optics, detectors, and end-station equipment, along with local, evolutionary changes to the storage ring itself. However, major accelerator upgrades are also being investigated. One very promising option that has been the subject of considerable research is the use of an energy recovery linac. In this option, APS would transition from a source based on a stored electron beam to one based on a continuously generated high-brightness electron beam from a linac. Such a source promises dramatically improved brightness and transverse coherence compared to third-generation storage rings, as well as distinctly different temporal properties.
ANL, Argonne
Funding: This work was supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
The Advanced Photon Source is filled for five weeks per year in a special bunch (hybrid) pattern of one large 16-mA (74-nC) bunch in a gap of 3 microseconds, and the remaining 86 mA in 8 trains of 7 consecutive bunches, forming a 500-microsecond-long bunch train. We are developing variations of this bunch pattern, which might have 3 large bunches equally spaced in the 3-microsecond gap in a 4-mA, 16-mA, and 8-mA distribution. The 500-microsecond-long bunch train could be changed to 2 or 3 bunch trains of 7 bunches. We report on the difficulties in bringing these into future operations: impedance-driven injection losses, sextupoles in injection section, lifetime and topup injection limit, and beam diagnostics responses to the patterns.
ANL, Argonne
Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC02-06CH11357.
An array of fused-silica, fiber optic bundles has been built to spatially monitor e-beam loss in the APS storage ring (SR). A prototype beam loss position monitor (BLPM) has been installed on unoccupied undulator straight sections. The BLPM allows for 6 fiber bundles, 3 above and 3 below the beam. The center bundles are aligned with the beam axis. Presently, 4 bundles are used, 3 above and one in the center position below the beam. Each bundle is 3 m in length and composed of 61 220-micron-diameter fibers for a total aperture of 2 mm. The first 30 cm of each bundle are aligned parallel to the beam in contact with the vacuum chamber. Light generated by fast electrons within the fibers is thought to come primarily from Cerenkov radiation. The rest of the fiber acts as a light pipe to transmit photons to shielded PMTs. Tests show good signal strength during stored-beam mode from Touschek scattering and deterministic losses that occur during top-up injection and beam dumps. Post-injection loss signals show spatial and temporal dynamics. Simulation work is expected to provide calibration for integrated losses that can be compared with progressive undulator demagnetization.
ANL, Argonne
Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357.
The Advanced Photon Source (APS), a third-generation synchrotron light source, has been in operation for eleven years. The monopulse radio frequency (rf) beam position monitor (BPM) is one of three BPM types now employed in the storage ring at the APS. It is a broadband (10 MHz) system designed to measure single-turn and multi-turn beam positions, but it suffers from an aging data acquisition system. The replacement BPM system retains the existing monopulse receivers and replaces the data acquisition system with high-speed analog-to-digital converters (ADCs) and a field-programmable gate array (FPGA) that performs the signal processing. The new system has been installed and commissioned in a full sector of the APS. This paper presents the results of testing of the beam position monitor which is now fully integrated into the storage ring orbit control and fast feedback systems.
ANL, Argonne
Funding: This work was supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CHlI357.
During an operating period in which a sextupole unknowingly connected with the wrong polarity resulted in reduced beam lifetime, a list of machine physics experiments and simulations were developed to identify possible gradient errors of one or more sextupole magnets. We tried tune dependence on orbit, response matrix measurements at different momenta, sector-wise chromaticity measurements, empirical search with sextupole harmonics, and guidance from tracking simulations. The practicality of each will be discussed.
ANL, Argonne
Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
Optimization of dynamic and momentum aperture is one of the most challenging problems in storage ring design. For storage-ring-based x-ray sources, large dynamic aperture is sought primarily to obtain high injection efficiency, which is important in efficient operation but also in protecting components from radiation damage. X-ray sources require large momentum aperture in order to achieve workable Touschek lifetimes with low emittance beams. The most widely applied method of optimizing these apertures is to minimize the driving terms of various resonances. This approach is highly successful, but since it is based on perturbation theory, it is not guaranteed to give the best result. In addition, the user must somewhat arbitrarily assign weights to the various terms. We have developed several more direct methods of optimizing dynamic and momentum aperture. These have been successfully applied to operational and design problems related to the Advanced Photon Source and possible upgrades.