PASOTRON™ high-energy microwave source

A unique, high-energy microwave source, called PASOTRON for Plasma-Assisted Slow-wave Oscillator has been developed. Similar to the Backward Wave Oscillator (BWO), the PASOTRON spontaneously generates microwave radiation by efficiently converting electron beam energy into electromagnetic radiation. The PASOTRON, however, utilizes a novel E-gun and plasma-filled slow-wave structure (SWS) to produce and propagate very long, high-power beam pulses which require no axial magnetic fields for transport. The long electron beam pulses are obtained from a Hughes Hollow-Cathode Plasma (HCP) E-gun, which employs a low-pressure glow discharge to provide a stable, high current-density electron source. Electrons from this source are accelerated through a multi-aperture array to produce a large area, high-current beam consisting initially of many individual beamlets. Since the device is operated in the ion focused regime, the plasma filling the SWS, space-charge neutralizes the beam, and the Bennett self-pinch compresses the beamlets and increases the beam´s current density. Experimental results from a PASOTRON tube designed to operate in a TM01 mode at C-band frequencies when driven by a 50-to-100-kV, 50-to-250 A electron beam are reported. Results show output power is in the l-to-4 MW range, for rf pulselengths up to 100 μsec, corresponding to an integrated energy per pulse of up to 300 J. Calculations show the E-beam to microwave-radiation power-conversion efficiency is ∼20%. Instantaneous bandwidth measurements further reveal that for the duration of the long ripulse the PASOTRONs oscillation center frequency maintains a narrow line <3MHz.