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Gierman, S. M.

Paper Title Page
TUPMS055 SPEAR3 Accelerator Physics Update 1311
  • J. A. Safranek, W. J. Corbett, S. M. Gierman, R. O. Hettel, X. Huang, J. J. Sebek, A. Terebilo
    SLAC, Menlo Park, California
  The SPEAR3 storage ring at Stanford Synchrotron Radiation Laboratory has been delivering photon beams for three years. We will give an overview of recent and ongoing accelerator physics activities, including 500 mA fills, work toward top-off injection, long-term orbit stability characterization & improvement, fast orbit feedback, new chicane optics, low alpha optics & short bunches, low emittance optics, and new insertion devices. The accelerator physics group has a strong program to characterize and improve SPEAR3 performance.  
FRPMS066 Commissioning the Fast Luminosity Dither for PEP-II 4165
  • A. S. Fisher, S. Ecklund, R. C. Field, S. M. Gierman, P. Grossberg, K. E. Krauter, E. S. Miller, M. Petree, N. Spencer, M. K. Sullivan, K. K. Underwood, U. Wienands
    SLAC, Menlo Park, California
  • K. G. Sonnad
    LBNL, Berkeley, California
  Funding: Supported by US DOE under contract DE-AC03-76SF00515.

To maximize luminosity, a feedback system adjusts the relative transverse (x,y) position and vertical angle (y') of the electron and positron beams at the interaction point (IP) of PEP-II. The original system sequentially moved ("dithered") the electrons in four steps per coordinate. Communication with DC corrector magnets and field penetration through copper vacuum chambers led to a full-cycle time of 10 s. Machine tuning can move the beams at the IP and so had to be slowed to wait for the feedback. A new system installed in 2006 simultaneously applies a small sinusoidal dither to all three coordinates at 73, 87 and 103 Hz. Air-core coils around stainless-steel chambers give rapid field penetration. A lock-in amplifier at each frequency detects the magnitude and phase of the luminosity's response. Then corrections for all coordinates are determined using Newton's method, based on convergence from prior steps, and are applied by the same DC correctors used previously but with only one adjustment per cycle for an expected ten-fold increase in speed. We report on the commissioning of this system and on its performance in maintaining peak luminosity and aiding machine tuning.