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The improvements of the dielectric materials are one of the most important parts for developing the compact and/or higher power insulators. The breakdown of the rf windows, which pass rf power and isolate vacuum, was induced by the multipactor and surface discharge. Both are related to the secondary electron emission (SEE) and surface charigng. The SEE from alumina materials are measured using a scanning electron microscope (SEM). The single-pulse and multi-pulse methods are applied for the SEE coefficients and surface charging measurements, respectively. The TiN coatings for multipactor suppression are also investigated from the view points of SEE and surface charging. Sapphire shows highest surface charging and has higher SEE coefficients with temperature increase. These results lead to the lower threshold of the electrical breakdown observed for the rf windows. It is confirmed that TiN coatings are effective for the decrease in SEE. The multipulse-measurements indicate TiN coatings lower the surface charging probably caused by the lower SEE.

Secondary Electron Emission from Alumina Materials Used for High-Power RF Windows