Supplementary Damping Systems for the International Linear Collider

Indispensable subsystems of the International Linear Collider (ILC) will be the damping rings, which will shrink the emittances of the electron and positron beams. This idea was first proposed by Amaldi [1]. Once the beams enter their respective main linacs, the ultra low emittances should already have been achieved in the damping rings, where the equilibrium emittances are determined by the balancing of radiation damping, quantum excitations, and intrabeam scattering. For the TESLA superconducting linac design, one wants horizontal/vertical normalized emittances of 10/0.03 μrad. Given the long TESLA bunch trains, 2820 particles per bunch with 337 nsec between bunches, the damping ring is driven to a large circumference, 17 km. Also, various schemes require kickers with fast rise and fall times. There are also the challenges of achieving good dynamic aperture and beam stability during the long damping period. Any methods of alleviating some of these difficulties deserve serious study.