Design and analysis on a 0.1‐THz second harmonic low‐voltage, low‐current gyrotron with complex cavity

Abstract

This article presents the design and analysis of a complex cavity that will be used in a 10 kW‐level 94 GHz second harmonic low‐current, low‐voltage gyrotron. The mode pair of TE+7.2/TE+7.3 is selected as the operating modes of the complex cavity. In cold‐cavity design, a throat is introduced in the complex cavity to increase the diffractive quality factor, which can make the gyrotron operate at low‐current and low‐voltage conditions. In hot‐cavity analysis, the beam‐wave interaction efficiency affected by different factors has been studied in detail. At the operating point with beam voltage of 32 kV and beam current of 1.5 A, the mode competition has been studied based on the analysis of starting current and a time‐dependent multifrequency code; the transverse velocity spread influence on the efficiency has also been investigated. The results indicate that the operating mode eventually dominates the mode selection, while the competing modes are all at noise level. Meanwhile, the interaction efficiency can keep more than 30% with maintaining the spread below 8%, and the output power can hold at 10 kW‐level when the spread is below 12%.