Design of a 1-THz Fourth-Harmonic Gyrotron Driven by Axis-Encircling Electron Beam

Abstract

In this paper, the design of a 4 th -harmonic gyrotron with 1-kW-level output power at 1 terahertz (THz) is presented. A unique advantage of this design is that, with a well-optimized magnetic-cusp large-orbit electron gun, the designed gyrotron can operate from 1 st harmonic to 4 th harmonic in multiple discrete bands by varying the operating voltage. By carefully balancing the competing modes, the gyrotron can be tuned to operate at six candidate modes, including TE1,2 for fundamental harmonic, TE2,3 and TE2,4 for 2 nd harmonic, TE3,5 and TE3,6 for 3 rd harmonic, and TE4,8 for 4 th harmonic interactions. As the main operating mode, the TE4,8 can generate a peak output power of 1.68 kW, with an efficiency of about 2.1%, and a magnetically controlled frequency tuning range of about 1.8 GHz around 1 THz. The impact of the longitudinal nonuniformity of the cavity at high-harmonic interaction was also studied. It shows a radial tolerance of several micrometers will significantly elevate the start-oscillation current and deteriorate output performance. This design is towards the development of a synthesizing THz source with ultra-wideband tuning capability ranging from the sub-millimeter-wave to 1-THz bands.Index Terms-high harmonic terahertz gyrotron, multi-mode switching, broad-range magnetic tuning.

Intrinsic resonance in gyrotron using non-resonant RF structure

“…Despite the potential challenges in wave coupling that may arise due to nearcutoff operation, the insights provided here are believed to shed light on the underlying mechanism for existing gyrotron devices. The current trend in gyrotron design is shifting toward the development of reflective-type gyro-backward wave oscillators (Rgyro-BWOs), 20,[55][56][57] which combine the high efficiency of the gyromonotron with the advantage of continuous frequency tunability found in gyro-BWOs. However, the underlying mechanism behind the operation of R-gyro-BWOs remains unclear.…”