Electromagnetic interaction of colliding beams on storage rings

When the beams cross each other in the intersection region of a storage ring, two distinct effects occur. A particle of one beam may undergo a fundamental interaction with a particle of the other beam. The average number of such events is equal to the product of the machine luminosity and the particle-particle total cross section. In contrast to what happens for these fundamental interactions, a particle of one beam passing through the interaction region will always be influenced by the electric and magnetic fields produced by the entire other beam. Clearly, this classical electromagnetic interaction between the two beams will perturb the motion of the particles circulating in the machine. The basic aspects of this beam-particle force are presented. The effect of this electrical force is quite different in the case of continuous (unbunched) proton beams which cross each other at the angle (as in the ISR at CERN and in ISABELLE at Brookhaven), as compared to the case of electron-positron bunches which collide head on (as in the SPEAR 2 ring and in PETRA and PEP).