In quasi optical gyrotrons, the angle between the electron beam and radiation beam has considerable influence on the gain, harmonic operation, and efficiency. The authors investigate its effect on the gain mechanism. Two regimes of operation are identified, namely, gain nearly proportional to l/sup 2/ (l is the interaction length) for small angles and gain nearly proportional to l/sup 3/ for large angles. The transition angle separating the two regimes is found and is approximately given by ( lambda /l)/sup 1/2/, where lambda is the wavelength. It is shown that by choosing the parameters appropriately, one can run the gyrotron in the high-gain response.
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