Secondary electron emission measurements of dielectric window materials

Dielectric window is an important component of high power microwave (HPM) generation device, however, breakdown easily occurs on vacuum/dielectric interface when HPM passes through dielectric window. Surface breakdown limits the generation and transmission of HPM, and becomes the bottle neck of HPM technology development. Secondary electron emission (SEE) plays an important role of dielectric window breakdown, so that the paper studies SEE coefficients of several dielectric window materials including polytetrafluoroethylene (PTFE), polyethylene (PE) and polymethylmethacrylate (PMMA) in vacuum. The measurements are carried out by single pulsed electron beams impacting the materials with energies of 0.6keV up to 5keV. First, we can get the primary current from the single pulse impacting aluminum. Then the secondary currents emitted from the samples are measured by the collector, which is applied to positive bias voltage (+23V) for ensuring the secondary electrons are mostly captured. The SEE coefficients δ increases with pulsed electron beam energies, then reaches the maximum, and finally decreases as beam energy continues growing. The result is that SEE coefficients δ of PTFE is the lowest, PE at the highest.