A silicon disk etched so that it contains a multitude of microscopic and thin window Fanes (micropanes) can potentially transmit a larger average electron beam current density and absorb a smaller fraction of the beam energy than a common metal foil window. The enhanced performance is achieved by a combination of decreased power loss due to the extremely small window thickness (similar to1 mum), and increased conductive cooling due to the small diameter (similar to 50 mum) of the micropanes and the large cross section of the honeycomb structure that supports the micropanes. Beam current densities up to 34 A/cm(2) are permitted within each micropane. When integrated over many micropanes across the face of a window, average current densities up to 1 A/cm(2) are permitted-at least three orders of magnitude larger than the < mA/cm(2) typical of foil windows. The small mass thickness yields high transparency, even for low energy beams. The transmission efficiency for a 100 keV beam is 99.5.