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Decker, F.-J.

 
Paper Title Page
MOPLS044 Luminosity Variations along Bunch Trains in PEP-II 640
 
  • F.-J. Decker, M. Boyes, W.S. Colocho, A. Novokhatski, M.K. Sullivan, J.L. Turner, S.P. Weathersby, U. Wienands, G. Yocky
    SLAC, Menlo Park, California
 
  In spring of 2005 after a long shut-down, the luminosity of the B-Factory PEP-II decreased along the bunch trains by about 25-30%. There were many reasons studied which could have caused this performance degradation, like a bigger phase transient due to an additional RF station in the Low-Energy-Ring (LER), bad initial vacuum, electron cloud, chromaticity, steering, dispersion in cavities, beam optics, etc. The initial specific luminosity of 4.2 sloped down to 3.2 and even 2.8 for a long train (typical: 130 of 144), later in the run with higher currents and shorter trains (65 of 72) the numbers were more like 3.2 down to 2.6. Finally after steering the interaction region for an unrelated reason (overheated BPM buttons) and the consequential lower luminosity for two weeks, the luminosity slope problem was mysteriously gone. Several parameters got changed and there is still some discussion about which one finally fixed the problem. Among others, likely candidates are: the LER betatron function in x at the interaction point got reduced, making the LER x stronger, dispersion reduction in the cavities, and finding and fixing a partially shorted magnet.  
MOPLS045 Achieving a Luminosity of 1034/cm2/s in the PEP-II B-factory 643
 
  • J. Seeman, J. Browne, Y. Cai, W.S. Colocho, F.-J. Decker, M.H. Donald, S. Ecklund, R.A. Erickson, A.S. Fisher, J.D. Fox, S.A. Heifets, R.H. Iverson, A. Kulikov, A. Novokhatski, V. Pacak, M.T.F. Pivi, C.H. Rivetta, M.C. Ross, P. Schuh, K.G. Sonnad, M. Stanek, M.K. Sullivan, P. Tenenbaum, D. Teytelman, J.L. Turner, D. Van Winkle, M. Weaver, U. Wienands, W. Wittmer, M. Woodley, Y.T. Yan, G. Yocky
    SLAC, Menlo Park, California
  • M.E. Biagini
    INFN/LNF, Frascati (Roma)
  • W. Kozanecki
    CEA, Gif-sur-Yvette
 
  For the PEP-II Operation Staff: PEP-II is an asymmetric e+e- collider operating at the Upsilon 4S and has recently set several performance records. The luminosity has exceeded 1x1034/cm2/s and has delivered an integrated luminosity of 728/pb in one day. PEP-II operates in continuous injection mode for both beams, boosting the integrated luminosity. The peak positron current has reached 2.94 A and 1.74 A of electrons in 1732 bunches. The total integrated luminosity since turn on in 1999 has reached over 333/fb. This paper reviews the present performance issues of PEP-II and also the planned increase of luminosity in the near future to over 2 x 1034/cm2/s. Upgrade details and plans are discussed.  
MOPLS049 Anomalous High Radiation Beam Aborts in the PEP-II B-factory 652
 
  • M.K. Sullivan, Y. Cai, S. DeBarger, F.-J. Decker, S. Ecklund, A.S. Fisher, S.M. Gierman, S.A. Heifets, R.H. Iverson, A. Kulikov, N. Kurita, S.J. Metcalfe, A. Novokhatski, J. Seeman, K.G. Sonnad, D. Teytelman, J.L. Turner, U. Wienands, D. Wright, Y.T. Yan, G. Yocky
    SLAC, Menlo Park, California
 
  The PEP-II B-factory at SLAC has recently experienced unexpected beam losses due to anomalously high radiation levels at the BaBar detector. The problem was finally traced to the occurrence of very high pressure (>100 nTorr) spikes that have a very short duration (few seconds). We describe the events and show analysis predicting where in the vacuum system the events originated and describe what was discovered in the vacuum system.  
MOPLS051 Tracking Down a Fast Instability in the PEP-II LER 658
 
  • U. Wienands, R. Akre, S.C. Curry, S. DeBarger, F.-J. Decker, S. Ecklund, A.S. Fisher, S.A. Heifets, A. Krasnykh, A. Kulikov, A. Novokhatski, J. Seeman, M.K. Sullivan, D. Teytelman, D. Van Winkle, G. Yocky
    SLAC, Menlo Park, California
 
  During Run 5, the beam in the PEP-II Low Energy Ring (LER) became affected by a predominantly vertical instability with very fast growth rate of 10…60/ms - much faster than seen in controlled grow-damp experiments - and varying threshold. The coherent amplitude of the oscillation was limited to approx. 1 mm pk-pk or less and would damp down over a few tens of turns; however, beam loss set in even as the measured amplitude damped, causing a beam abort. This led to the conclusion that the beam was actually blowing up. The presence of a 2 nu_s line in the spectrum suggested a possible head-tail nature of the instability, although chromaticity was not effective in raising the threshold. In this paper we will describe the measurements and data taken to isolate and locate the cause of the instability and, eventually, the discovery and fix of the root cause.  
MOPLS052 Luminosity Improvement at PEP-II Based on Optics Model and Beam-beam Simulation 661
 
  • Y. Cai, W.S. Colocho, F.-J. Decker, Y. Nosochkov, P. Raimondi, J. Seeman, K.G. Sonnad, M.K. Sullivan, J.L. Turner, M. Weaver, U. Wienands, W. Wittmer, M. Woodley, Y.T. Yan, G. Yocky
    SLAC, Menlo Park, California
 
  The model independent analysis (MIA) has been successfully used at PEP-II to understand machine optics and improve the luminosity. However, the rate of success was limited because the improvement of optics does not necessarily lead to increase of luminosity. Recently, we were able to reconstruct MIA model in a full optics code, LEGO, and used it to calculate complete lattice and beam parameters. These parameters were fed to the beam-beam code, BBI, to understand the luminosity histories at PEP-II over the past year. Using these tools, we optimized the luminosity by varying the beam parameters such as emittance. Finally, we implemented an optimized solution with a set of asymmetric horizontal orbit bumps into the machines during a delivery shift with a few percentage gain in luminosity. The solution was retained at PEP-II machines along with the luminosity. Later, these asymmetric bumps also played a vital role in reaching 1x1034cm-2s-1 as the beam currents increased.  
WEOAPA01 Demonstration of Energy Gain Larger than 10GeV in a Plasma Wakefield Accelerator 0
 
  • P. Muggli, S. Deng, T.C. Katsouleas, E. Oz
    USC, Los Angeles, California
  • D. Auerbach, C.E. Clayton, C. Huang, D.K. Johnson, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori, M. Zhou
    UCLA, Los Angeles, California
  • I. Blumenfeld, F.-J. Decker, P. Emma, M.J. Hogan, R. Ischebeck, R.H. Iverson, N.A. Kirby, P. Krejcik, R. Siemann, D.R. Walz
    SLAC, Menlo Park, California
 
  We have recently demonstrating the excitation of accelerating gradients as large as 30 GV/m* using the ultra-short, 28.5 GeV electron bunches now available at the Stanford Linear Accelerator Center. As a result, the electrons in the back of the bunch gained about 3 GeV over the 10 cm-long plasma with a density of ?2.5x1017 e /cm-3. In recent experiments, energy gains in excess of 10 GeV, by far the largest in any plasma accelerators, have been measured over a plasma length of ?30 cm. Moreover, systematic measurements show the scaling of the energy gain with plasma length and density, and show the reproduceability and the stability of the acceleration process. These are key steps toward the application of beam-driven plasma accelerators or plasma wakefield accelerators (PWFA) to doubling the enregy of a future linear collider without doubling its length. We are preparing for experiments to be performed in February-March 2006 aiming at doubling the energy of the 28.5 GeV beam over a plasma length of less than one meter, a distance two thousand times shorter than the accelerator that created the incoming beam. The latest experimental results will be presented.

*M. J. Hogan et al. Phys. Rev. Lett. 95, 054802, 2005.

 
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WEPCH062 Precision Measurement and Improvement of Optics for e+, e- Storage Rings 2065
 
  • Y.T. Yan, Y. Cai, W.S. Colocho, F.-J. Decker, J. Seeman, M.K. Sullivan, J.L. Turner, U. Wienands, M. Woodley, G. Yocky
    SLAC, Menlo Park, California
 
  Through horizontal and vertical excitations, we have been able to make a precision measurement of linear geometric optics parameters with a Model-Independent Analysis (MIA). We have also been able to build up a computer model that matches the real accelerator in linear geometric optics with an SVD-enhanced Least-square fitting process. Recently, with the addition of longitudinal excitation, we are able to build up a computer virtual machine that matches the real accelerators in linear optics including dispersion without additional fitting variables. With this optics-matched virtual machine, we are able to find solutions that make changes of many normal and skew quadrupoles for machine optics improvement. It has made major contributions to improve PEP-II optics and luminosity. Examples from application to PEP-II machines will be presented.