Measurements of secondary electron emission from dielectric window materials

Dielectric window is an important component of high-power microwave (HPM) devices. However, surface breakdown easily occurs at the vacuum/dielectric interface when HPM pass through the dielectric window. This greatly limits transmission of HPM and makes the window a bottle neck of HPM technology development. Secondary electron emission (SEE) from dielectric window plays an important role in its surface breakdown. This paper studies the total SEE (including true secondary electrons and backscattered electrons) coefficients of several inorganic and organic dielectric materials including polytetrafluoroethylene, polyethylene, alumina ceramic, and machinable ceramic. The measurements are implemented by using pulsed electron beam impacting the materials with energies from 200 eV to 5 keV. In addition, surface desorbed gas property is studied with the quadrupole mass spectrometer. The performances of different materials are evaluated. The obtained results are useful for the selection of HPM window materials.