A Novel High Efficiency 1.5 MW, 110 GHz Gyrotron with HE11 Output for Plasma Heating

Electron Cyclotron Resonance Heating (ECRH) has emerged as one of the most important tools for plasma heating and stabilization in magnetically confined fusion devices. In particular, ECRH is the most effective tool for suppressing Neoclassical Tearing Modes (NTM) in both currently operating tokamaks such as DIII-D, General Atomics and future tokamaks such as ITER. Current generation of MW gyrotrons in the 110-170 GHz range have been limited to & lt;50% total efficiency in theory and in practice, only 40-45% efficiency values have been demonstrated. Though there are many causes for low experimentally achieved efficiencies, it has been determined by experimental studies that the After Cavity Interaction (ACI) in megawatt gyrotrons leads to 10- 15% points decrease in total efficiency. In this Phase I work, we propose to design a novel magnetic system, a new cavity and a novel internal mode transformer to mitigate the ACI effect to achieve ~60% efficiency. The novel internal mode launcher will result in direct HE11 output from the gyrotron in a corrugated waveguide thus avoiding the need for a large and expensive Matching Optics Unit (MOU) which is necessary for coupling the output power from current generation of gyrotrons (with TEM00-like output) to the HE11 mode in a corrugated waveguide transmission line. The combination of high efficiency with the simpler and less expensive coupling mechanism will result in a more compact and less expensive gyrotron system for plasma heating. This collaborative project aims to bring together the expertise of Bridge12 Technologies, a start-up company based in Framingham, MA focused in the area of high power, millimeter wave and terahertz source, component design and manufacturing with the well-established expertise and facilities of the SLAC National Accelerator Laboratory in the development of multi-megawatt microwave sources and components. A successful achievement of the goals of this project in the proposed Phase I and a future Phase II will lead to the establishment of an alternative source in the United States for high power gyrotrons