Beam-Beam Interaction Effects in the Fermilab Collider

Abstract

Fermi National Accelerator Laboratory's Collider is the first collider to implement a helical orbit separation scheme for colliding protons and antiprotons. Six antiproton bunches collide head-on with six proton bunches at the two high energy physics detector locations in the ring. The orbits are separated in both the horizontal and vertical planes at all other collision points. A study of the dependence of the beam-beam interaction on transverse beam separation is presented. Beam-beam experiments in the Collider determined that the beam-beam interaction is the predominant nonlinear force which drives seventh order resonances in the Collider. These odd-ordered resonances were observed to cause large particle losses in the presence of a transverse beam separation or crossing angle at an interaction point. This observation led to a method of "helical orbit tuning" using electrostatic separators and resulted in a 5% increase in the luminosity during Collider Run IA. Independant tuning of beam separation and crossing angle at head-on collision points now provides a luminosity enhancement in routine Collider operations. Beam-beam experiments were compared with beam-beam simulations to produce an understanding of colliding beam behavior when two particle distributions collide with a transverse beam separation. An experimental measure of particle losses due to resonant excitation at different beam separations showed good agreement with beam-beam simulation results. This comparative agreement extends across a range of beam separations and particle tunes. This investigation lays a foundation for using beam-beam simulations as a predictive tool for defining minimum beam separation criteria for stable Collider operation.