Effects of tapered tubes on long-pulse microwave emission from intense e-beam gyrotron-backward-wave-oscillators

Experiments are reported on tapered-tube versus uniform-tube, gyrotron-backward-wave-oscillators (4.5-6 GHz) driven by an intense electron beam with parameters: 0.8 MV, 1-4 kA, and pulselength (0.5-1 /spl mu/s). Results show that, compared to a uniform interaction tube, a gyro-BWO with a 10% downtapered tube produces the following effects: 1) highest microwave peak-power (up to about 100 MW in internal tube), a factor of 2 higher than the uniform tube, 2) more reproducible long-pulse (400-500 ns) emission, and 3) the largest inferred-integrated energy (factor of 2.5-3 increase). Experiments show high power microwave spikes with lower power plateaus. Experimental observations are in qualitative agreement with MAGIC code simulations of uniform and tapered-tube gyro-BWO's.<
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