Recent Publications

Establishing a Coherent Qualification Pathway for Fusion Technologies

Amanda Louise Allison

Development and Application of Collective Thomson Scattering Diagnostics for Energetic and Bulk Ion Measurements in the Large Helical Device

Masaki Nishiura, Yuusuke Yamaguchi, Shin Kubo, Kenji Tanaka, Naoki Kenmochi, Ryoma Yanai, Ryosuke Seki, Hideo Nuga, Takashi Shimozuma, Yoshinori Tatematsu, et al.

National Institute for Fusion Science, University of Fukui, Technical University of Denmark, The University of Tokyo, Chubu University

Numerical Optimization of Neon Soft X-ray Emission in a Spherical Plasma Focus Device with Lee Code

M. I. Nayeem, M. A. Malek

Khulna University, International University of Business Agriculture and Technology (IUBAT)

Development of Charge Exchange Spectroscopy in LHD

Mikirou Yoshinuma, Katsumi Ida, Tatsuya Kobayashi

National Institute for Fusion Science, Research Institute for Applied Mechanics, Kyushu University, The Graduate University for Advanced Studies, SOKENDAI

Charge exchange spectroscopy is widely used in fusion plasma research as a method for measuring ion temperature distribution and plasma flow velocity. In the LHD, charge exchange spectroscopy has been applied to observe impurity density distribution, hydrogen/deuterium isotope ratio distribution, and distortion of the ion velocity distribution function using multiple systems that employ high-throughput spectrometers, multi-channel optical fibers, and high-speed image detectors. In the measurement of the hydrogen/deuterium ratio, we succeeded in the analysis by combining it with velocity distribution measurement using a conventional system. In the measurement of the ion velocity distribution function, we were able to grasp the overall situation by combining one with high spatial resolution and a system with high temporal resolution.

An Integrated AHP-SWOT Analysis on the Strategic Transition of Traditional Oil and Gas Companies to Fusion Energy in China

Chao Guo, Ya Yuan, Yongxin Zheng, Bo Wang, Xingang Li

China Petroleum Engineering and Construction Corporation, CNPC Capital Company Limited, Fusion Energy Technology Company Limited

Spectroscopy Using a Schwob-Fraenkel Grazing Incidence Spectrometer

Chihiro Suzuki, Hisamichi Funaba, Naoki Tamura

National Institute for Fusion Science, The Graduate University for Advanced Studies, SOKENDAI, Max-Planck-Institut für Plasmaphysik

This article reviews the technological details of a 2-m Schwob-Fraenkel soft X-ray multichannel spectrometer (SOXMOS) which has been installed in the Large Helical Device (LHD) to study impurity behaviors. Experimental setup of the SOXMOS operated in the duo-multichannel detector mode is described together with the peripheral equipment and remote control systems customized for the LHD. The absolute wavelength is carefully calibrated using the positions of reference lines based on the two different fitting methods. The data acquisition and registration are completely automated, and the secondary physical data resulting from the wavelength calibration and the peak detection are also made available for all the LHD users. The SOXMOS data have been widely used for various research topics relevant to impurity transport as well as atomic physics.

Plasma Disruption Prediction on the Nanchang Spherical Tokamak: A Comparative Study of Models Based on Sliding Window Statistical Features

Li Zhang, Xincheng Xiong, Xiaochang Chen, Sanqiu Liu, Xiaolan Liu

Nanchang University

Criteria for the economic viability of fusion power plants

D. G. Whyte, A. Lo, R. Bielajew, M. Hancock, R. Moeykens, G. Shaw

Rutherford Energy Ventures, Massachusetts Institute of Technology, Santa Fe Institute

Review of High-Power Microwave Transmission System for ECH in LHD

Ryoma Yanai, Shin Kubo, Takashi Shimozuma, Yasuo Yoshimura, Masaki Nishiura, Hiroe Igami, Hiromi Takahashi, Toru Ii Tsujimura, Naoki Kenmochi, Sakuji Kobayashi, et al.

National Institute for Fusion Science, The Graduate University for Advanced Studies, Kyoto Fusioneering Ltd, Chubu University, National Institute for Quantum Science and Technology

Electron cyclotron heating (ECH) is one of the auxiliary heating methods employed in many magnetically confined fusion devices. In the Large Helical Device (LHD), the ECH system - including high-power gyrotrons, transmission lines, and mirror antennas – has played an important role in improving plasma parameters and realizing a variety of plasma experiments. Highly efficient transmission lines capable of withstanding high-power microwaves are essential to deliver high-power microwaves emitted from gyrotrons. In addition, mirror antennas are important for ensuring that the ECH power is absorbed at the intended location. In this paper, the ECH transmission system, focusing on the associated components used in high-power microwave transmission lines and various mirror antennas prepared for the LHD experiment, is reviewed.

A Method of (in)validating the Projected Levelized Cost of Electricity of Fusion Power

Adam Jackson

Real-Time Control System for Electron Cyclotron Heating Injection on LHD

Naoki Kenmochi, Tohru Ii Tsujimura, Yoshinori Mizuno, Masaki Nishiura, Kota Okada, Yasuo Yoshimura, Hiroe Igami, Hiromi Takahashi, Ryoma Yanai, Toshiki Takeuchi, et al.

National Institute for Fusion Science, The Graduate University for Advanced Studies, Kyoto Fusioneering Ltd., The University of Tokyo, Nagoya University

Real-time control of electron cyclotron heating (ECH) is critical for optimizing plasma performance and preventing instabilities in advanced fusion devices. We present a comprehensive real-time ECH control system developed on the Large Helical Device (LHD) that enables real-time adjustment of microwave heating in response to evolving plasma conditions. A field-programmable gate array (FPGA) controller actuates the ECH launchers, enabling millisecond-level adjustments of both injection angle and polarization to maximize absorption as plasma density and temperature profiles change. To compute suitable settings rapidly, a generative adversarial network (GAN) model was trained on thousands of past LHD discharges and ray-tracing simulations of ECH to generate control parameters for the deposition position and polarization. In high-density LHD experiments, another machine-learning-based prediction framework enabled the first active avoidance of radiative collapse. The predictor identified an impending collapse about 65 milliseconds in advance, triggering automated ECH power re-targeting and a cutoff of fueling that stabilized the plasma beyond the conventional density limit. These developments demonstrate how real-time ECH control, together with machine-learning-assisted prediction and inference, can sustain stable, high-performance plasmas, highlighting a pathway toward long-duration, steady-state fusion operations.

Experimental Data Management System for Long-Term Fusion Experiments

Masahiko Emoto, Hideya Nakanishi, Masanobu Yoshida, Ryuichi Sakamoto

National Institute for Fusion Science, National Institutes of Natural Sciences, The Graduate University for Advanced Studies

The LHD experiment started in 1998 at the National Institute for Fusion Science and has continued for nearly 30 years. The experimental data obtained in these experiments are stored as physical data in the Kaiseki Data Server and made available to the public using an open data server. Through the experience of developing and operating this server, this paper discusses the problems that can occur in data management systems in long-term projects such as the LHD experiment and how they can be improved.

STEP Fusion: Overview of the Concept Design for the Spherical Tokamak for Energy Production and Lessons Learnt

Stuart I. Muldrew, Jonathan Keep, Chris Waldon

UK Fusion Energy Ltd