Beam-beam effects of gear changing in ring-ring colliders

Abstract

In ring-ring colliders, the collision frequency determines the bunch structures, e.g., the time between the bunches in both rings should be identical. Because of relatively low relativistic speed of the hadron beam in sub-TeV hadron-hadron-and electron-ions colliders, scanning the hadron beam's energy would require either a change in the circumference of one of the rings, or a switching of the bunch (harmonic) number in a ring. The later would cause so-called gear changing, i.e., the change of the colliding bunches turn by turn. In this article, we study the difficulties in beam dynamics in this gear-changing scheme.

First Direct Observations of Gear-Changing In A Collider

“…While there is potential for ongoing experiments with gear-changing in DESIREE, a better understanding of the beam-beam effect requires an experiment in a machine such as RHIC, or a dedicated facility. A machine with a similar footprint to DESIREE but using electrons, and having dedicated diagnostics would not only be able to perform gear-changing, but would have a beam-beam effect sufficient to reach the predicted instability threshold calculated in [4].…”

“…There is also a problem caused by each beam's abort gap which means that when gearchanging reaches these gaps the beams will not receive any type of beam-beam effect. A theoretical treatment was performed for possible use in RHIC to reduce systematic errors [4]. An experiment to determine the effects of abort gaps was performed using an electron lens to simulate the interactions [5].…”