Stochastic cooling

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Stochastic cooling is a form of particle beam cooling.^[1] 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.

The technique was invented and applied at the Intersecting Storage Rings,^[2] and later the Super Proton Synchrotron (SPS), at CERN in Geneva, Switzerland, by Simon van der Meer,^[3] a physicist from the Netherlands. It was used to collect and cool antiprotons—these particles were injected into the Proton-Antiproton Collider, a modification of 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 proposed the Proton-Antiproton Collider. This experiment discovered the W and Z bosons, fundamental particles that carry the weak nuclear force.

Before the shutdown of the Tevatron on the 30th of September 2011,^[4] Fermi National Accelerator Laboratory used stochastic cooling in its antiproton source.^[5] The accumulated antiprotons were sent to the Tevatron to collide with protons at two collision points: the 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,^[6] operationally used beginning in 2006. Since 2012 RHIC has 3D operational stochastic cooling,^[7] i.e. cooling the horizontal, vertical, and longitudinal planes.