Radiation-triggered breakdown phenomena in high-energy e+e- colliders

The frequency of breakdown phenomena in a HV system under ultrahigh vacuum, can be increased by orders of magnitude by the presence of radiation, either in the form of electromagnetic waves (laser and UV light, synchrotron light, X-rays, γ rays) or charged particles and ions. Both types of radiation are abundant in high-energy e⁺e^- colliders, and studies of the effect of a particular radiation source in this difficult environment are subject to many limitations. Thus, the principal strategy is to reduce the radiation flux incident on critical devices by absorbing the electromagnetic radiation or by trapping the charged particles. However, in the case of the `pretzel´ separation project for CERN´s large electron positron (LEP) collider, this strategy failed. As a result many experiments have been carried out in order to achieve a better understanding of radiation-triggered breakdown phenomena. Observations made in some other e⁺e^- colliders are also reported