Nobuaki Ohno

Abstract The Large Helical Device (LHD), the largest superconducting helical system in the world, is equipped with advanced heating and diagnostic tools, facilitating plasma control and physics research. Data assimilation was employed for electron temperature control using a real-time Thomson scattering system and real time prediction code. A virtual LHD environment enabled visualization of escaping high-energy tritium ions and demonstrated that these ions impact the rear side of the divertor plate. Pioneering results crucial to plasma control have also been achieved. Real-time wall conditioning using Lithium granule dropping improved bulk ion energy and particle transport while simultaneously enhancing the heavy impurity transport. Progress has also been made in the investigation of turbulence-driven transport. At the confinement bifurcation, ion-scale turbulence decreased, while electron-scale turbulence increased. A change in the anisotropy of turbulent eddies was also observed at the confinement bifurcation. Coexistence of local and non-local turbulence was identified in electron-scale turbulence. Non-local turbulence exhibited the rapid spatial propagation of perturbations throughout the plasma, while local turbulence followed the temperature gradient. A transition between drift-wave turbulence and magnetohydrodynamics (MHD) turbulence was observed with the turbulence minimized at the transition condition. Machine learning analysis was employed to evaluate the temperate and density conditions of this turbulence transition. Then, real-time control of fueling and heating was applied to maintain the turbulence transition condition, improving the energy confinement enhancement factor by 20%. In addition, evidence was obtained for collisionless ion heating by energetic-ion-driven geodesic acoustic modes and MHD bursts. These achievements represent unique contributions to the development of fusion reactors.

Abstract This paper discusses the importance and advancements of visualization technology in fusion science research. First, visualization is an essential process for analyzing experimental and simulation data, aiding in the understanding of complex phenomena such as plasma. It emphasizes that, instead of conventional two-dimensional graphs, virtual reality (VR) technology enables researchers to observe data in three dimensions. This approach leads to a more intuitive understanding of complex phenomena. Additionally, VR technology provides an environment where multiple researchers can simultaneously discuss and analyze plasma physics, making it highly useful for research. Furthermore, VR plays a crucial role in effectively communicating research findings to the general public in an accurate and accessible manner. At the National Institute for Fusion Science, a VR visualization system has been established to efficiently analyze large-scale simulation data using CAVE-type VR devices. The latest technology, such as head-mounted displays (HMDs), has also been introduced. The applications of visualization technology are not limited to fusion science but are expected to expand into other fields as well, making it a promising area of ongoing development. This paper presents key visualization research achievements conducted at the National Institute for Fusion Science. We are also developing new capabilities to display both CAD and simulation data on HMDs as we port the VR software originally designed for large CAVE-type systems. These developments will also be described.