Performance of the PEP-II B-Factory Collider at SLAC
PEP-II is an e+e-asymmetric B-Factory Collider located at SLAC operating at the Upsilon 4S resonance (3.1 GeV x 9 GeV). It has reached a luminosity of 9.21×1033/cm2/s and has delivered an integrated luminosity of 710 pb-1in one day. PEP-II has delivered, over the past six years, an integrated luminosity to the BaBar detector of over 262 fb-1. PEP-II operates in continuous injection mode for both beams boosting the integrated luminosity. The peak positron current has reached 2.45 A in 1588 bunches. Steady progress is being made in reaching higher luminosity. The goal over the next several years is to reach a luminosity of 2.1x1034/cm2/s. The accelerator physics issues being addressed in PEP-II to reach this goal include the electron cloud instability, beam-beam effects, parasitic beam-beam effects, high RF beam loading, shorter bunches, loweryinteraction region operation, and coupling control. Figure 1 shows the PEP-II tunnel.
A TURN-BY-TURN, BUNCH-BY-BUNCH DIAGNOSTICS SYSTEM FOR THE PEP-II TRANSVERSE FEEDBACK SYSTEMS ∗
A diagnostics system centered around commercial fast 8-bit digitizer boards has been implemented for the transverse feedback systems at PEP-II. The boards can accumulate bunch-by-bunch position data for 4800 turns (35 ms) in the x plane and the y plane. A dedicated trigger chassis allows to trigger the data acquisition on demand, or on an injection shot to diagnose injection problems, and provides gating signals for grow-damp measurements. Usually, the boards constantly acquire data and a beam abort stops data acquitision, thus preserving the last 4800 turns of position information before a beam abort. Software in a local PC reads out the boards and transfers data to a fileserver. Matlab-based data analysis software allows to present the raw data but also higher-level functions like spectra, modal analysis, spectrograms and others. The system has been instrumental in diagnosing beam instabilities in PEP. This paper will describe the architecture of the system and its applications.
Unidirectional hexagonal rare-earth disilicide nanowires on vicinal Si(100)-2×1
Rare-earth disilicide nanowires grown on vicinal Si(100) with a miscut of 2–2.5° toward the [110] azimuth at 600 °C were studied by scanning tunneling microscopy and compared with those grown on flat Si(001). In contrast to rare-earth disilicide nanowires grown on flat Si(100) surfaces, the nanowires grow unidirectionally along the [01̄1] direction of the vicinal Si(100) surface. Rare-earth disilicide nanowires form bundles composed of single nanowire units on both flat and vicinal surfaces. Yet, on the vicinal surface, the bundle width is comparable to the width of the terrace. The average nanowire length on the vicinal substrate is longer than that on the flat substrate. Scanning tunneling spectroscopy shows that the rare-earth disilicide nanowires have metallic properties.