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Decker, F.-J.

Paper Title Page
WEPP041 High-current Effects in the PEP-II Storage Rings 2611
 
  • U. Wienands, W. X. Cheng, W. S. Colocho, S. DeBarger, F.-J. Decker, S. Ecklund, A. S. Fisher, D. Kharakh, A. Krasnykh, A. Novokhatski, M. K. Sullivan
    SLAC, Menlo Park, California
 
  High beam currents, 2A(HER) & 3A(LER), in PEP-II has been a challenge for the vacuum system. For the ~1 cm long bunches peak currents reach 50 A. Thus modest impedances can give rise to voltage spikes and discharges. A weakness was uncovered during Run 6: rf seals at the "flex flanges" that join the HER arc dipole and quadrupole chambers became a source of an increasing number of HER beam aborts. Vacuum activity was seen and thermal sensors on these flanges saw temperature spikes. Inspection of the seals found arcing and melting, prompting us to replace all of these seals with an improved design using Inconel instead of GlidCop fingers. We believe the GlidCop fingers do not maintain elasticity and hence can not follow chamber motion due to thermal effects. The Run 7 startup confirmed the success of this repair. However, high bunch current in the LER caused breakdown in a LER kicker. This limited the LER bunch current to about 1 mA. Inspection revealed damage to one of the recently added Macor pins that help support the electrodes. Failure analysis revealed heating of the pin & post-facto modeling shows high fields coming from a combination of HOM impedance and high peak currents.  
WEPP044 Commissioning the 90° Lattice for the PEP II High Energy Ring 2617
 
  • W. Wittmer, Y. Cai, W. X. Cheng, W. S. Colocho, F.-J. Decker, S. Ecklund, A. S. Fisher, Y. Nosochkov, A. Novokhatski, M. K. Sullivan, U. Wienands, Y. T. Yan, G. Yocky
    SLAC, Menlo Park, California
 
  In order to benefit from further reduction of the vertical IP beta function of the PEP-II HER the bunch length should be reduced. This will be achieved by changing the phase advance from 60 deg to 90 deg in the four arcs not adjacent to the IR region, thus reducing momentum compaction by about 30% and reducing bunch length from a present 12 mm down to 8.5 mm at low beam current. In preparation to implement the 90 deg lattice the main HER quadrupole and sextupole strings and their power supplies have been reconfigured. Compared to the 60 deg lattice it was expected that dynamic aperture and injection will be more difficult. The synchrotron tune initially will be lower but can be brought back by raising the rf voltage. Beam emittance is held at 48 nmr by introducing a significant dispersion beat in the arcs. The lattice was successfully commissioned at currents up to 800mA in August 2007. In this paper we will compare the actual machine with the predicted behaviour, explain the correction strategies used and give an overall assessment of the operation and the benefit of the new lattice configuration.  
THPC007 Permanent Magnet Skew Quadrupoles for the Low Emittance LER Lattice of PEP-II 2987
 
  • F.-J. Decker, S. D. Anderson, D. Kharakh, M. K. Sullivan
    SLAC, Menlo Park, California
 
  The vertical emittance of the low energy ring (LER) in the PEP-II B-Factory was reduced by using skew quadrupoles consisting of permanent magnet material. The advantages over electric quadrupoles or rotating existing normal quadrupoles are discussed. To assure a high field quality a Biot Savart calculation was used to cancel the natural 12-pole component by using different size poles over a few layers. A magnetic measurement confirmed the high quality of the magnets. After installation and adjusting the original 12 skew and 16 normal quadrupoles the emittance contribution from the region close to the interaction point, which was the biggest part in the original design, was considerably reduced.  
THPC008 Constants and Pseudo-constants of Coupled Beam Motion in the PEP-II Rings 2990
 
  • F.-J. Decker, W. S. Colocho, M.-H. Wang, Y. T. Yan, G. Yocky
    SLAC, Menlo Park, California
 
  Constants of beam motion help as cross checks to analyze beam diagnostics and the modeling procedure. Pseudo-constants, like the betatron mismatch parameter or the coupling parameter det C, are constant till certain elements in the beam line change then. This can be used to visually find the non-desired changes, pinpointing errors compared with the model.