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 No. DE-AC02-06CH11357.
The response matrix fit is routinely used at APS for linear optics correction. The high accuracy of the method enables us to measure the variation of betatron phase advance around the ring with rf frequency. This variation can be used to calculate local chromaticity. Such measurements were first performed at the APS at the moment when a sextupole was mistakenly connected with the wrong polarity. Local chromaticity calculations clearly pointed to the location of the sextupole error. Results and details of the measurements are reported and discussed.
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.
An energy recovery linac (ERL) is one of the candidates for an upgrade of the Advanced Photon Source (APS). In addition to the APS ring and full-energy linac, our design also includes a large turn-around arc that could accommodate new x-ray beamlines as well. In total, the beam trajectory length would be close to 3 km. The ERL lattice has strong focusing to limit emittance growth, and it includes strong sextupoles to keep beam energy spread under control and minimize beam losses. As in storage rings, trajectory errors in sextupoles will result in lattice perturbations that would affect delivered x-ray beam properties. In storage rings, the response matrix fit method is widely used to measure and correct linear lattice errors. Here, we explore the application of the method to the linear lattice correction and coupling correction of an ERL.
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.
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 storage ring has several bunch fill patterns for user operation. In some fill patterns the single-bunch beam charge is as high as 16 mA. We installed a bunch-to-bunch feedback system that aims to overcome high-charge beam instability and reduce the required chromatic correction. Due to the drive strength limitation, we decided to first commission the feedback system in the vertical plane. We present our preliminary results, some of the issues that we have experienced and resolved, and our plan to expand the system to the horizontal plane.