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Sebek, J. J.

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TUPMS051 Low Alpha Mode for SPEAR3 1308
  • X. Huang, W. J. Corbett, Y. Nosochkov, J. A. Safranek, J. J. Sebek, A. Terebilo
    SLAC, Menlo Park, California
  In the interest of obtaining shorter bunch length for shorter X-ray pulses, we have developed a low-alpha operational mode for SPEAR3. In this mode the momentum compaction factor is reduced by a factor of 21 or more from the usual achromat mode by introducing negative dispersion at the straight sections. We successfully stored 100~mA with the normal fill pattern at a lifetime of 30hrs. The bunch length was measured to be 6.9ps, compared to 17ps in the normal mode. In this paper we report our studies on the lattice design and calibration, orbit stability, higher order alpha measurement, lifetime measurement and its dependence on the sextupoles, injection efficiency and bunch lengths.  
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.  
FRPMS065 Bunch Length Measurements in SPEAR3 4159
  • W. J. Corbett, A. S. Fisher, X. Huang, J. A. Safranek, J. J. Sebek
    SLAC, Menlo Park, California
  • A. H. Lumpkin
    ANL, Argonne, Illinois
  • W. Y. Mok
    Life Imaging Technology, Palo Alto, California
  Funding: Work supported by US Department of Energy Contract DE-AC03-76SF00515 and Office of Basic Energy Sciences, Division of Chemical Sciences.

In the nominal SPEAR3 storage ring optics, the natural radiation pulse length is 40ps fwhm per bunch. Due to the double-bend achromat lattice configuration, it is relatively straightforward to reduce the momentum compaction factor (α) and hence reduce the bunch length by modest values. In this paper we present streak camera measurements of the bunch length in the nominal optics, and with ~α/20 and α/50 optics as a function of single-bunch current. The results demonstrate <10ps fwhm radiation pulses with up 5x108 particles/bunch (~100μ amp). Radiation pulse power, bunch length scaling and broadband impedance estimates are discussed.

FRPMS084 Detection of Instumental Drifts in the PEP II LER BPM System 4261
  • W. Wittmer, A. S. Fisher, D. J. Martin, J. J. Sebek
    SLAC, Menlo Park, California
  Funding: US-DOE

During the last PEP-II run a major goal was to bring the Low-Energy Ring optics as close as possible to the design. Sudden artificial jumps of the orbit, which were regularly observed by a large number of BPMs during routine operation, were interfering with this effort. The source of the majority of these jumps had been traced to the filter-isolator boxes (FIBs) near the BPM buttons. A systematic approach to find and repair the failing units had been developed and implemented. Despite this effort, the instrumental orbit jumps never completely disappeared. To trace the source of this behavior a test setup, using a spare Bergoz MX-BPM processor (kindly provided by SPEAR III at SSRL) was connected in parallel to various PEP-II BPM processors. In the course of these measurements a slow instrumental orbit drift was found which was clearly not induced by a moving positron beam. Based on the size of the system and the limited time before the end of PEP II an accelerator improvement project was initiated to install BERGOZ BPM-MX processors close to all sextupoles.