A Coaxially Loaded Helical Slow-wave Structure for TWTs

27^th International Conference on Infrared and Millimeter Waves

September 22-26, 2002, San Diego, CA, USA

A 42 GHz, 200 kW Second Harmonic Gyrotron

M. V. Kartikeyan^a, E. Borie^a, B. Piosczyk^a, and M. Thumm^a,b

^{a Forschungszentrum Karlsruhe, Institut für Hochleistungsimpuls- und Mikrowellentechnik (IHM)
Postfach 3640, 76021 Karlsruhe, Germany

^{bUniversität Karlsruhe, Institut für Höchstfrequenztechnik und Elektronik,
Kaiserstr. 12, 76128 Karlsruhe, Germany}

Abstract

The feasibility of second harmonic operation of a 42 GHz, 200 kW gyrotron for a small experimental Tokamak has been studied as a logical extension of our earlier conceptual design of a similar tube operating in the fundamental of the cyclotron harmonic. Mode competition and mode selection are carefully investigated by considering various candidate modes operating in the first and second cyclotron harmonics respectively and the TE_4,2 mode at s=2 is chosen as the operating mode. A suitable cold cavity is considered with quality factor around 650. Self-consistent calculations are carried out and power and efficiencies are computed for a typical set of beam parameters. The results show that for an accelerating voltage of 68 kV and beam current of 18 A, an output power of well over 200 kW, CW and efficiency around 20% in the TE_4,2 mode can be reached under second harmonic operation.}