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.
Measurement of the Luminous-Region Profile at the PEP-II Ip, And Application to e&#177;Bunch-Length Determination
The three-dimensional luminosity distribution at the interaction point (IP) of the SLAC B-Factory is measured continuously, using e<sup>+</sup>e<sup>-</sup>→ e<sup>+</sup>e<sup>-</sup>, μ<sup>+</sup>μ<sup>-</sup>events reconstructed online in the BABAR detector. The centroid of the transverse luminosity profile provides a very precise and reliable monitor of medium- and long-term orbit drifts at the IP. The longitudinal centroid is sensitive to variations in the relative RF phase of the colliding beams, both over time and differentially along the bunch train. The measured horizontal r.m.s. width of the distribution is consistent with a sizeable dynamic-β effect; it is also useful as a benchmark of strong-strong beam-beam simulations. The longitudinal luminosity distribution depends on the e<sup>±</sup>bunch lengths and vertical IP β-functions, which can be different in the high- and low-energy rings. Using independent estimates of the β functions, we analyze the longitudinal shape of the luminosity distribution in the presence of controlled variations in accelerating RF voltage and/or beam current, to extract measurements of the e<sup>+</sup>and e<sup>-</sup>bunch lengths.
PULSE: a high-repetition-rate linac driver for x-ray FELs
We describe a staged concept for a linac-based freeelectron laser providing coherent tuneable VUV and soft X-ray output with pulse lengths down to 10 fs or less. Use of 1.3 GHz cryomodules operated with CW RF will allow flexible pulse patterns at potentially very high repetition rates up to 1 MHz. We consider the options for FELs that may be included in a facility of this type.