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The VEBA high-current, relativistic electron accelerator has been designed and constructed at NRL for application in the study of high-power microwave sources. To meet the requirements of this study, the accelerator was designed for operation in either a short (60 nsec) or long (2.2 Â¿sec) pulse mode. The short-pulse mode has been in operation for nearly two years and has proven to be an extremely reliable design. The design of the long-pulse mode is now complete and component fabrication will soon be underway. The pulse-forming network in the short-pulse mode is an unbalanced, water Blumlein with an output impedance of 9.2Â¿ The Blumlein is pulse charged by a 17 stage Marx generator which has a series capacitance of 29.4 nF. By transmission along a tapered coaxial line, the output pulse is transformed to 20 Â¿ and the voltage developed across a matched load increased to a maximum of 2.5 MV. The proposed conversion to the long-pulse mode will require that the Blumlein and transformer sections be removed and the diode assembly be attached directly to the oversized Marx tank. The direct coupling between the Marx and the Blumlein will then be replaced by two, nested, water capacitors which are shunted by spiral inductors. When coupled in series with the Marx, this output filter will form a three-section, voltage-fed, Guillemin (type A), pulse-forming network with a characteristic impedance of 40 Â¿ and a maximum output voltage of 0.9 MV.