INVESTIGATIONS ON HIGH-POWER SUB-TERAHERTZ GYROTRONS

Abstract

Thermonuclear fusion holds significant potential as a feasible approach for the development of clean and sustainable green energy source to address the ever-expanding global energy demands. However, this ambitious endeavor is accompanied by significant technical obstacles. The initiation of a fusion reaction necessitates extreme temperatures inside the reactor, reaching around 150 million Kelvin. This extreme condition is required for the confinement of plasma and the sustained ignition of fusion reactions. Within the domain of plasma fusion experiments, Electron Cyclotron Resonance Heating and Current Drive (ECRH&CD) have emerged as the most efficient methods for heating magnetically confined plasmas. Gyrotrons have become vital components in experimental tokamaks, primarily because of their ability to generate powerful millimeter and sub-THz waves. These devices play a crucial role in applications related to ECRH&CD. These devices are capable of generating power ranging from several hundred kilowatts to multiple megawatts. The importance of these devices is emphasized by their incorporation into state-of-the-art fusion tokamaks (machines that confine plasma), such as the International Thermonuclear Experimental Reactor (ITER), ASDEX-Upgrade, DIII-D, EAST, KSTAR, and W7-X stellarator. Particularly, W7-X stellarator showcases the implementation of ten gyrotrons, each capable of providing an impressive 1MW of continuous wave (CW) power at a frequency of 140 GHz, specifically for plasma heating. Furthermore, a pioneering endeavor is currently underway to install the first batch of 24CW gyrotrons, each capable of delivering 1MW of power at 170 GHz, to support plasma heating in the ITER tokamak located in Cadarache, France. The ITER project is a significant endeavor with the aim of validating nuclear fusion as a viable commercial, large-scale, and clean energy production method, aspiring to generate a remarkable 500MWof electrical power while ensuring the stable confinement of fusion plasma over extended periods. The necessity of high-power gyrotrons for Electron Cyclotron Resonance Heating (ECRH) in controlled fusion has been thoroughly demonstrated through their development and rigorous testing. An essential realization is that the energy output of a fusion reactor is directly proportional to the number of fusion reactions occurring within its core. Consequently, the fusion community places significant emphasis on achieving larger core sizes, a focal point to enhance energy generation and reduce electricity production costs in future fusion tokamak. As the journey towards commercial fusion power continues, gyrotrons face novel challenges. Future tokamak designs demand gyrotrons capable of operating at higher frequencies and power levels to meet evolving challenges. Additionally, ensuring the reliability and enhanced tritium self-sufficiency of gyrotrons is imperative—a critical aspect for the operation of the futuristic fusion tokamak. The recent development of the DEMOnstration (DEMO) tokamak, representing the first prototype of a commercial