Stochastic cooling and the accumulation of antiprotons

1. A general outline of the project The large project mentioned in the motivation of this year’s Nobel award in physics includes in addition to the experiments proper described by C. Rubbia, the complex machinery for colliding high-energy protons and antiprotons (Fig. 1). Protons are accelerated to 26 GeV/c in the PS machine and are used to produce p’s in a copper target. An accumulator ring (AA) accepts a batch of these with momenta around 3.5 GeV/c every 2.4 s. After typically a day of accumulation, a large number of the accumulated (~10) are extracted from the AA, reinjected into the PS, accelerated to 26 Gev/c and transferred to the large (2.2 km diameter) SPS ring. Just before, 26 Gev/c protons, also from the PS, have been injected in the opposite direction. Protons and antiprotons are then accelerated to high energy (270 or 310 Gev) and remain stored for many hours. They are bunched (in 3 bunches of about 4 ns duration each) so that collisions take place in six well-defined points around the SPS ring, in two of which experiments are located. The process is of a complexity that could only be mastered by the effort and devotion of several hundreds of people. Only a small part of it can be covered in this lecture, and I have chosen to speak about stochastic cooling, a method that is used to accumulate the antiprotons, and with which I have been closely associated.