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Emery, L.

Paper Title Page
MPPE064 Dynamic Aperture Study and Lifetime Improvement at the Advanced Photon Source 3632
 
  • V. Sajaev, L. Emery
    ANL, Argonne, Illinois
 
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

Over past few years, the optics of the Advanced Photon Source storage ring was optimized to provide lower natural emittance. Presently, APS operates at 2.5 nm-rad emittance. The optimization was done at the expense of stronger sextupoles and shorter lifetime. Here we present our work on measurement and understanding the dynamic aperture of APS in low-emittance mode. We found good agreement between the dynamic aperture measurements and that of the model derived from the response matrix analysis. Based on the model, we were able to increase the lifetime significantly by optimizing sextupoles, correcting optics, moving working point, and adjusting rf voltage. The higher lifetime allowed us to decrease operating coupling from 2.5% to 1%.

 
TOAB009 Generation of Short X-Ray Pulses Using Crab Cavities at the Advanced Photon Source 668
 
  • K.C. Harkay, M. Borland, Y.-C. Chae, G. Decker, R.J. Dejus, L. Emery, W. Guo, D. Horan, K.-J. Kim, R. Kustom, D.M. Mills, S.V. Milton, G. Pile, V. Sajaev, S.D. Shastri, G.J. Waldschmidt, M. White, B.X. Yang
    ANL, Argonne, Illinois
  • A. Zholents
    LBNL, Berkeley, California
 
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

There is growing interest within the user community to utilize the pulsed nature of synchrotron radiation from storage ring sources. Conventional third-generation light sources can provide pulses on the order of 100 ps but typically cannot provide pulses of about 1 ps that some users now require to advance their research programs. However, it was recently proposed by A. Zholents et al. to use rf orbit deflection to generate subpicosecond X-ray pulses.* In this scheme, two crab cavities are used to deliver a longitudinally dependent vertical kick to the beam, thus exciting longitudinally correlated vertical motion of the electrons. This makes it possible to spatially separate the radiation coming from different longitudinal parts of the beam. An optical slit can then be used to slice out a short part of the radiation pulse, or an asymetrically cut crystal can be used to compress the radiation in time. In this paper, we present a feasibility study of this method applied to the Advanced Photon Source. We find that the pulse length can be decreased down to a few-picosecond range using superconducting crab cavities.

*A. Zholents et al., NIM A 425, 385 (1999).

 
RPAE002 Coupling Correction of a Circularly Polarizing Undulator at the Advanced Photon Source 805
 
  • L. Emery
    ANL, Argonne, Illinois
 
  Funding: This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

The electromagnetic Circularly Polarizing Undulator (CPU) installed at the Advanced Photon Source (APS) storage ring produces skew quadrupole field errors, which were initially corrected by a small skew quadrupole magnet at one end of the device. Because the storage ring is operated at 1% coupling or less, a correction not located at the source inside the CPU is insufficient, as we have confirmed in simulation. Adding a skew coil at the other end of the CPU allows us to make a complete correction of the coupling source in the undulator. Correction setpoints are determined by APS's general optimizing software with the vertical beam size of a x-ray pinhole image as a readback.

 
RPAE003 Optimization and Modeling Studies for Obtaining High Injection Efficiency at the Advanced Photon Source 871
 
  • L. Emery
    ANL, Argonne, Illinois
 
  Funding: This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

In recent years, the optics of the Advanced Photon Source storage ring has changed to lower equilibrium emittance (2.5 nm-rad) but at the cost of stronger sextupoles and stronger nonlinearities, which have reduced the injection efficiency from 100% in the high emittance mode. Over the years we have developed a series of optimization, measurement and modeling studies of the injection process, which allows us to obtain or maintain low injection losses. For example, the trajectory in the storage ring is optimized with trajectory knobs for maximum injection efficiency. This can be followed by collecting first-turn trajectory data, from which we can fit the initial phase-space coordinates. The model of the "optimized" trajectory would show whether the beam comes too close to a physical aperture in the injection magnets. Another modeling step is the fit and correction of the transfer line optics, which has a significant impact on phase-space matching.

 
RPAE071 Touschek Lifetime and Undulator Damage in the Advanced Photon Source 3835
 
  • M. Borland, L. Emery
    ANL, Argonne, Illinois
 
  Funding: Work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

The Advanced Photon Source (APS) has two insertion devices (IDs) with small-aperture vacuum chambers. The full vertical aperture in these chambers is 5 mm, while the inboard horizontal aperture is 15 mm. These devices suffer significant radiation damage, requiring frequent retuning. We recently hypothesized that the damage resulted from loss of Touschek-scattered particles on the horizontal aperture of the chambers. This results partly from the smallness of the aperture and partly from the pattern of the dispersion and beta functions in the low-emittance APS lattice. The horizontal scrapers were originally at a high-dispersion location, but, in the low-emittance lattice, they are at a fairly low-dispersion location. Similarly, the dispersion at the IDs was originally zero but is now close to the maximum for the lattice. In this paper, we summarize simulations and experiments that support our hypothesis and discuss plans to remedy the problem.

 
RPPP047 Global Optimization of Damping Ring Designs Using a Multi-Objective Evolutionary Algorithm 2962
 
  • L. Emery
    ANL, Argonne, Illinois
 
  Funding: This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

Several damping ring designs for the International Linear Collider have been proposed recently. Some of the specifications, such as circumference and bunch train, are not fixed yet. Designers must make a choice anyway, select a geometry type (dog-bone or circular), an arc cell type (TME or FODO), and optimize linear and nonlinear part of the optics. The design process include straightforward steps (usually the linear optics), and some steps not so straightforward (when nonlinear optics optimization is affected by the linear optics). A first attempt at automating this process for the linear optics is reported. We first recognize that the optics is defined by just a few primary parameters (e.g., phase advance per cell) that determine the rest (e.g., quadrupole strength). In addition to the exact specification of circumference, equilibrium emittance and damping time there are some other quantities which could be optimized that may conflict with each other. A multiobjective genetic optimizer solves this problem by producing a population of best-ranked solutions on a multi-dimensional surface from which one solution can be chosen by the designer. The application of the NSGA-II optimizer to a damping ring of FODO cells is presented.

 
RPPP051 Characterization of a 6-km Damping Ring for the International Linear Collider 3147
 
  • A. Xiao
    Fermilab, Batavia, Illinois
  • L. Emery
    ANL, Argonne, Illinois
 
  Several damping ring designs for the International Linear Collider have been proposed recently. One particular design has a circumference of 6 km (hoping to take advantage of future kicker technology advances), TME arc cells, and 77 m of 2 T wigglers. Several beam dynamics characterizations and optimizations are reported. We used the accelerator code elegant for matching and tracking, and a 100-CPU linux cluster to provide high throughput.