Electron cloud in wigglers

Substantial electron densities may accrue inside the wigglers of future linear-collider damping rings, since the wiggler photon flux can only partially be absorbed by antechambers. In an operating positron ring, at DAFNE, a fast instability with electron-cloud signature has indeed been observed after modifications to the wiggler field. Simulations of electron-cloud build up in wigglers allow us to explore the dependence of the electron density and decay time on the magnet and beam parameters. Without additional countermeasures, the simulated electron densities easily exceed the thresholds of electron-driven single and multi-bunch instabilities. The latter are modelled by separate computer programmes. In this report, simulations of electron build up and instabilities are presented for the damping rings of ILC and CLIC, as well as for DAFNE.