Faraday cups are being used as an important diagnostic tool in the laser community for measuring current densities of electron-beam pumped devices. However, a design standard based on a thorough experimental investigation appears to be lacking. Conflicts certainly exist over cup design and operation limitations, in particular, operation in a vacuum vs gas and gas composition and pressure are foremost concerns. The aim of our work is to develop a Faraday cup for operation at relatively low current densities by first using the simplest concepts and then carefully measuring its characteristics in different operating conditions. A Marx powered vacuum diode delivers ≈375-keV electrons at ≈30 A/cm2 over a 10- × 70-crn area. A magnetic guide field of 2 kG is also used.

© 1989 Optical Society of America

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