Stochastic Cooling

Stochastic cooling is a form of particle beam cooling. It is used in some particle accelerators and storage rings to control the emittance of the particle beams in the machine. This process uses the electrical signals that the individual charged particles generate in a feedback loop to reduce the tendency of individual particles to move away from the other particles in the beam. It is accurate to think of this as thermodynamic cooling, or the reduction of entropy, in much the same way that a refrigerator or an air conditioner cools its contents.

The technique was invented and applied at the Intersecting Storage Rings, and later the Super Proton Synchrotron, at CERN in Geneva, Switzerland by Simon van der Meer, a physicist from the Netherlands. It was used to collect and cool antiprotons--these particles were injected into the SPS with counter-rotating protons and collided at a particle physics experiment. For this work, van der Meer was awarded the Nobel Prize in Physics in 1984. He shared this prize with Carlo Rubbia of Italy, who conducted the physics experiment that took advantage of this breakthrough. This experiment discovered the W and Z bosons, fundamental particles that carry the weak nuclear force.

Fermi National Accelerator Laboratory continues to use stochastic cooling in its antiproton source. The accumulated antiprotons are used in the Tevatron to collide with protons to create collisions at CDF and the D0 experiment.

Stochastic cooling in the Tevatron at Fermilab was attempted, but was not fully successful. The equipment was subsequently transferred to Brookhaven National Laboratory, where it was successfully used in a longitudinal cooling system in RHIC, operationally used beginning in 2006. Since 2012 RHIC has 3D operational stochastic cooling, i.e. cooling the horizontal, vertical, and longitudinal planes.