Multipactor coatings for sapphire windows using remote plasma assisted deposition

Abstract

Single crystal sapphire provides several properties advantageous for high power RF windows, including high strength, low loss, and clear visual detection of impurities and material defects. These should allow applications for both high peak and average power operation. In fact, sapphire windows are commonly used in gyrotrons producing more than 500 kW of average power. Their use for peak power applications, however, has been prevented by poor adhesion of sputtered multipactor coatings. Previous efforts to develop high peak power sapphire windows failed when minor processing arcs removed the coating1. This presentation describes adaptation of plasma processes to apply TiN to the crystal sapphire surface. This creates a molecular bond that can survive high temperature furnace operations as well as arcing during high power processing.