V.L. Bakunin – Junior Research Scientist, Institute of Applied Physics of RAS (N. Novgorod)

E-mail: knightrider7@yandex.ru

M.Yu. Glyavin – Head of Laboratory, Institute of Applied Physics of RAS (N. Novgorod)

E-mail: glyavin@appl.sci-nnov.ru

Yu.V. Novozhilova – Senior Research Scientist, Institute of Applied Physics of RAS (N. Novgorod)

E-mail: julia.novozhilova2009@yandex.ru

A.S. Sedov – Research Scientist, Institute of Applied Physics of RAS (N. Novgorod) E-mail: anton-sedov@mail.ru

The possibility of high-efficiency single-mode regimes in a submegawatt-power 250-GHz gyrotron, which is developed for the DEMO project, is studied. We use two numerical models: i) a stationary single-mode model with non-fixed field structure and electron velocity spread and ii) a non-stationary multimode model in the fixed field approximation. In the first model, an efficiency of about 40% is obtained for a beam current of about 20 A. In the second model, different current and voltage turn-on scenarios are considered. It is shown that for these scenarios a single-mode high-efficiency regime is possible within a fairly broad band of cyclotron frequency mismatch. Stability of such a regime with respect to the excitation of spurious modes is studied.

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