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.
Experimental Study of Crossing-Angle and Parasitic-Crossing Effects at the PEP-II E+E-Collider
In a series of dedicated accelerator experiments, we measure the dependence of the PEP-II luminosity performance on small horizontal crossing angles and on the horizontal separation at the first parasitic crossing. The experiment is carried out by varying the IP angle of one of the beams in two different bunch patterns, one with and one without parasitic crossings. The measurements show satisfactory agreement with three-dimensional beam-beam simulations.
IR UPGRADE PLANS FOR THE PEP-II B-FACTORY*
PEP-II, the SLAC, LBNL, LLNL B-factory has achieved a peak luminosity of over 9×10 33 cm -2 s -1 , more than 3 times the design luminosity, and plans to obtain a luminosity of over 1×10 34 cm -2 sec -1 in the next year. In order to push the luminosity performance of PEP-II to even higher levels an upgrade to the interaction region (IR) is being designed. In the present design, the interaction point (IP) is a head-on collision with two strong horizontal dipole magnets located between 21-70 cm from the IP that bring the beams together and separate the beams after the collision. The first parasitic crossing (PC) is 63 cm from the IP in the present by2 bunch spacing. Future improvements to PEP-II performance include lowering the βy * values of both rings. This will increase the βy value at the PCs which increases the beambeam effect at these non-colliding crossings. Introducing a horizontal crossing angle at the IP quickly increases the beam separation at the PCs but recent beam-beam studies indicate that a significant luminosity reduction occurs when a crossing angle is introduced at the IP. We discuss these issues and describe the present interaction region upgrade design.