Second-harmonic operation of coaxial gyrotrons - towards a proof-of-principle experiment

Abstract

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 employs the 2 MW-170 GHz coaxial gyrotron for ITER at Forschungszentrum Karlsruhe, Germany, which is designed to operate with the TE/sub 34,19/ 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 TE/sub 34,19 /mode (or some other mode of similar eigenvalue) can be excited at 170 GHz as a second-harmonic mode.