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A research approach is described for obtaining kilojoule microwave pulses of microsecond duration at 1.3 GHz from the relativistic klystron amplifier. Achieving kilojoule microwave pulses requires extending electron beam pulse durations and maximizing the microwave extraction efficiency at the fundamental frequency. An electron beam diode has been constructed that delivers peak currents in excess of 5 kA with a monotonically increasing current pulse exceeding durations of 1 [Mu]s at beam kinetic energies above 400 keV. Close attention has been given to minimizing the current losses from the diode. Maximum microwave extraction efficiency at the fundamental frequency has been related to the beam bunching amplitude and output cavity shunt impedance in terms of a simple circuit theory. The circuit theory predictions have been tested by particle-in-cell code calculations of the electron beam interactions with the proposed cavity structures. The successful cavity structures have been constructed and are awaiting testing.

Experiments at the microsecond pulse length have demonstrated that the virtual-cathode oscillator generates narrow-band (0.3% bandwidth) microwave pulses when the virtual cathode is surrounded by a resonant cavity and is driven by an appropriate electron beam. This result is a significant departure from the behavior of a free-running virtual-cathode oscillator where the frequency depends on the (current [density).sup.1/2]. This paper describes the long-pulse experimental results.