PEP-II, the "B factory" now being built at the Stanford Linear Accelerator Center, will re-use not only the tunnel of the old Positron-Electron Project but also a substantial amount of PEP's hardware. It also takes advantage of SLAC's famous "two-mile linac," a unique resource that will build upon its nearly three decades of achievement by serving as the injector for PEP-II.
Like any large accelerator, PEP-II is as much a feat of engineering as of science. The luminosity of the PEP-II beams imposes tremendous synchrotron-radiation heat loads that must be disposed of; essentially the vacuum chamber has to double as a heat sink for a powerful x-ray laser. Meanwhile, high-performance electronic control systems, as well as rf "gymnastics," must deal with familiar beam-control issues and also coupled-bunch instabilities caused by the beams "talking to" one another with electromagnetic fields.
The difference in the energies of the colliding beams -- electrons at about 9 GeV colliding with positrons at 3.1 GeV -- causes the center of mass of the collision to move in the laboratory frame of reference. This separates the ephemeral decay products in space (and, equivalently, time), making them easier to track. The collision energy is at a "resonance" called Upsilon (4S) that produces especially copious pairs of B mesons and their antiparticles.
An early tangible example of progress on this challenging machine is the acceleration cavity (shown here in low-power prototype form),
which is designed to shunt the disruptive higher-order cavity modes into external absorbers
while the fundamental mode accelerates the beam. The feasibility of the damping scheme
was demonstrated in a test setup at the Lambertson Beam Electrodynamics
Laboratory here.
Other recent achievements include some of the magnet systems for the low-
energy ring, which are being designed and built in collaboration with the Institute of High
Energy Physics in Beijing.
Return to the AFRD PEP-II page.
Return to the Summary of Programs on the AFRD Homepage.
The administrative information on the AFRD Homepage is applicable to this page.
