[en] In electron-positron storage rings the damping of particle oscillations is achieved by synchrotron radiation. Since this effect is practically absent in heavy-particle accelerators, multiple accumulation of particles is achieved by electron cooling. The method is as follows. A beam of electrons with the same average velocity and direction as that of the heavy particles is injected into one of the straight sections of a heavy-particle storage ring. The Coulomb interaction results in an exchange of energy between two kinds of particles, and if the electron beam is sufficiently monochromatic and has parallel particle trajectories, it will act as a refrigerator and absorb excess energy of the hot gas of heavy particles. In a coordinate system moving with the average particle velocity, this mixture of two intersecting beams is similar to a two-component plasma in which a temperature-equalizing process occurs. Results are given of experiments done in 1974-1975 on electron cooling of a proton beam. Although some of these results have been published, the more important results are included for completeness. Electron cooling makes possible multiple stacking of heavy particles. Studies have shown that by using this technique it is possible to stack intense antiproton beams that produce a luminosity of greater than or equal to 10³¹ cm-² sec-¹ of the proton-antiproton colliding beams