Accelerator Update

About the Fermilab Accelerators

Fermilab's Antiproton Source is not an accelerator, but it is vital to the collider physics program. Scientists often refer to the Antiproton Source as a Pbar because the symbol for an antiproton is a "p" with a bar over it.

The components of the Antiproton Source

The Antiproton Source at Fermilab consists of three main components:

Target
The antiproton target is located in the tunnel between the Main Injector ring and the Pbar ring, just outside of the rings themselves. The Main Injector sends 120 GeV protons to a nickel target. (GeV stands for a billion electron volts and represents how much energy a particle carries.) It takes one hundred thousand to one million protons to make a single antiproton. Once produced, the antiprotons are directed to the Debuncher. The target is actually part of the Debuncher system.

Debuncher
The Debuncher is a triangular-shaped synchrotron with a radius of 75 meters. (Synchrotron in this case means that the particles cycle around the machine.) It can accept 8 GeV protons from the Main Injector for beam studies, and 8 GeV antiprotons from the target station. Its primary purpose is to reduce the initial scattering of the antiprotons caused by their creation. There are also systems (beam-cooling systems) that act to make a denser beam.

The Debuncher maintains the beam at a constant energy of 8 GeV. There are three RF systems used in the Debuncher; one for rotating antiproton bunches and thereby cooling the beam, one for maintaining a bunch gap, and the third for diagnostics and beam studies. (RF stands for Radio Frequency, which is the electromagnetic energy used to shape and accelerate particles. A bunch is simply a group of particles.)

Accumulator
The Accumulator is the second synchrotron of the antiproton source and serves as a storage ring. It has also a triangular shape and is housed in the same enclosure as the Debuncher. All of the antiprotons made by the debuncher are stored here at 8 GeV and cooled until needed. (Cooling refers to the physical size of the beam and its momentum spread. When you cool a beam you make it a denser beam by forcing the particles into a smaller area.)

The Accumulator consists of four RF systems: one for moving the antiprotons to the center of the Accumulator beam pipe (the 'core'), one for capturing a portion of the core and moving it towards the extraction orbit, a third for stabilizing and shaping the beam, and the fourth is used for diagnostics. The Accumulator sends an 8 GeV antiproton beam to the Main Injector.