Advanced Design Studies of Key Components for a Triple-Frequency 42-/84-/95-GHz Gyrotron Output System

This article presents the design, simulation, and optimization of the key components of an advanced output system for a triple-frequency gyrotron operating at 42 GHz (<bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TE</b> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}_{\textbf {6,2}}$</tex-math> </inline-formula>), 84 GHz (<bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TE</b> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}_{\textbf {10,4}}$</tex-math> </inline-formula>), and 95 GHz (<bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TE</b> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}_{\textbf {12,4}}$</tex-math> </inline-formula>). The gyrotron generates the output power up to 200 kW at the desired frequencies with efficiency exceeding 40%, suitable for various applications in thermonuclear fusion reactors, including plasma start-up, current drive, and RF heating. Key components include a nonlinear taper (NLT), a quasi-optical launcher (QOL), a sapphire Brewster window, and a matching optics unit (MOU). The geometry of these components is optimized using the in-house tool package Gyrotron Design Studio (GDS V. 2024). In addition, commercial packages, Launcher Optimization Tool (LOT) and Surf3D, are used for designing QOL. Gaussian mode content factors of the output beams from the launcher are greater than 98% for all frequencies. The sapphire Brewster window enhances beam transport efficiency, while the MOU, featuring two beam-shaping mirrors, ensures optimal beam quality and effective coupling of the Gaussian beam to the corrugated waveguide. This study demonstrates the successful application of advanced design and optimization methods, using both proprietary and commercial simulation tools to achieve a high-performance output system for the triple-frequency gyrotron.