Collective effects in the NLC damping ring designs

In this paper, we give an overview of collective effects and related issues in the damping rings for the NLC. The main damping ring will have a maximum average current of 1 A in four bunch trains which are separated by 60-80 ns, allowing the fast kickers to inject and extract individual trains. Each bunch train consists of 75-90 bunches, separated by 1.4 ns, with a maximum bunch population of 1.5×10¹⁰. Because of the large average current, coupled bunch instabilities are a potential problem; these can be driven by the ring impedance or by a collective beam-ion instability. In addition, because the ring has a very small momentum compaction and synchrotron tune, potential well distortion and the microwave instability could be important. Finally, because of the very small beam emittances, the intrabeam scattering is significant. In the next sections, we will describe the present state of our calculations. We begin by describing the vacuum chamber design and RF cavities. We then discuss the longitudinal and transverse coupled bunch instabilities, the potential well distortion and the microwave instability, and finally, mode-coupling, ion effects, and intrabeam scattering