On high gradient insulators

Summary form only given. High gradient insulators (HGI) are periodic stacks of insulator-metal-insulator layers with vacuum surface breakdown properties superior to ordinary insulators. HGIs are natural candidates as insulating walls of reduced size vacuum devices. Moreover, since an HGI contains periodically distributed metallic layers it can block electromagnetic radiation in places where pulsed high voltage insulation is required at the same time, i.e. to avoid beam breakup instability in intense beam accelerators. We have been able to develop a relatively simple theoretical model which explains the reasons for the suppression of vacuum breakdown on HGI surfaces. The model is based on the study of the distribution of the electric fields closest to the HGI surface and the trajectories of the secondary electrons in the initial stages of the avalanche. We have also built HGI´s and performed experiments which support our theoretical predictions.