Second-Harmonic Operation of Coaxial Gyrotrons

- Towards a Proof-of-Principle Experiment -

K. A. Avramides, J. L. Vomvoridis, and B. Piosczyk¹

School of Electrical and Computer Engineering, National Technical University of Athens,

Association EURATOM-Hellenic Republic, Zographou GR-15773, Greece

1Forschungszentrum Karlsruhe, IHM, Association EURATOM-FZK, Postfach 3640, D-76021 Karlsruhe, Germany

e-mail: koavr@central.ntua.gr

We discuss the possibility of a proof-of-principle experiment regarding the excitation of a high-order mode interacting with the electrons at the second harmonic of the cyclotron frequency in a coaxial gyrotron cavity with a longitudinally corrugated inner conductor. The experiment will employ the 2 MW – 170 GHz coaxial gyrotron for ITER at Forschungszentrum Karlsruhe, Germany, which is designed to operate with the TE34,19 mode at the fundamental cyclotron frequency. Our study suggests that by using about half the magnetic field and modifying the coaxial cavity to a reasonable extent, the TE34,19 mode (or some other mode of similar eigenvalue) can be excited at 170 GHz as a second-harmonic mode.