EFFICIENCY AND START-OSCILLATION CONDITIONS IN NONUNIFORM BACKWARD-WAVE OSCILLATORS
MICHIGAN UNIV ANN ARBOR ELECTRON PHYSICS LAB
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The effect of several kinds of nonuniformities in the circuit phase velocity and beam potential on the start-oscillation conditions of an O-type BWO were investigated. The nonuniformities include linear, quadratic and exponential circuit phase velocity tapers and linear, quadratic, exponential and sinusoidal voltage gradients. It is shown that under certain conditions the taper may be employed to either reduce the startoscillation current or to suppress backward-wave oscillations in forward-wave amplifiers. Circuit phase velocity tapers for achieving phasefocusing and thus enhancing the efficiency of O-type BWOs are derived. Employing such a circuit taper in an experimental S- band BWO resulted in efficiency improvement factors of 1.2 to 2.0 to 1.0 over a frequency range of 2.0 to 4.0 gc. Efficiency enhancement through utilization of multisegment depressed collectors is investigated. Optimum collector segment voltages for achieving optimum efficiencies under typical operating conditions were determined and are presented. The utilization of prebunched beams in BWOs is considered and the effect on the start-oscillation conditions and efficiency is determined.
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