This paper describes the performance of the thin-film windows used in a new sealed-tube electron gun. Measurements include beam current, power, and power density along with window transmission, temperature, electron scattering and window life tests. A number of novel beam diagnostic tools were developed as part of this effort. Results are compared to Monte Carlo computer predictions and show good agreement. Transmitted beam powers in excess of 200 watts have been achieved, with current densities exceeding 30 milliamperes per square centimeter at sixty kilovolts beam energy. Predicted window wearout time exceeds several thousand hours at a current density of two milliamperes per square centimeter and a beam accelerating voltage of 60 kilovolts. This work was carried out under a Cooperative Research and Development Agreement (CRADA) between Lawrence Livermore National Laboratory and American International Technologies, Inc.