World-Class Measurement System Capable of Long-Term, Multi-Point Simultaneous Measurement of Plasma State Constructed

Mitsubishi Electric Corporation

Kyoto University

National Institute for Fusion Science

Plasma Measurement System Configuration

Mitsubishi Electric Corporation (hereafter, Mitsubishi Electric), Kyoto University (hereafter, Kyoto University) Institute of Advanced Energy, and National Institute for Fusion Science (hereafter, NIFS) have constructed a world-class (※1) microwave plasma measurement system for fusion energy (※2) capable of long-term, multi-point simultaneous measurement of plasma states. Furthermore, the successful demonstration of this system was achieved on the fusion experimental device "Heliotron J" (※3) owned by Kyoto University.

Mitsubishi Electric, Kyoto University, and NIFS will promote the development of plasma measurement technology essential for the social implementation of fusion energy.

Fusion energy is expected to be a next-generation energy source for realizing a decarbonized society. The Japanese government is promoting research and development and industry-academia-government collaboration with a view to power generation demonstrations in the 2030s through the "Fusion Energy Innovation Strategy" (※4) and related policies. For the social implementation of fusion energy, the establishment of highly reliable measurement technology that can grasp plasma states in real-time, which is indispensable for controlling fusion plasma at temperatures exceeding 100 million degrees Celsius, is required. Microwave measurement technology is considered promising as one such technology. Microwave measurement technology is characterized by its ability to install critical equipment away from the plasma, even within a fusion reactor where equipment is susceptible to damage from neutron irradiation. Mitsubishi Electric, Kyoto University, and NIFS have been jointly working on the advancement and device implementation of microwave measurement technology for fusion energy since 2025.

This system uses microwaves from a frequency comb (※5) that simultaneously contain multiple frequency components, enabling the simultaneous acquisition of reflected signals corresponding to multiple measurement points in the plasma. Furthermore, by adopting a dual-comb down-conversion method (※6) in the reception system, which can reduce the load on high-frequency signal processing, long-term measurement over the entire discharge has been made possible. This has achieved world-class performance capable of simultaneous measurement at up to 34 points (※7) over long periods, and demonstration success on "Heliotron J" has been achieved.

This development achievement was presented at the "EPS Plasma Physics Conference 2026" (※8), an international conference held in the UK from June 29 to July 3.

Development Features

1. Achieved world-class measurement performance enabling simultaneous measurement of up to 34 points over long periods

・ When microwaves are incident on plasma, microwaves are scattered and reflected by the plasma's electron density (cutoff density) (※9) corresponding to the frequency. The reflected microwaves undergo a frequency change due to the Doppler effect (※10) according to the rotation speed of the reflection layer. Using microwaves from a frequency comb enables simultaneous measurement of frequency changes at multiple points.

・ This measurement system enables simultaneous measurement of up to 34 points by using a frequency comb with 34 "teeth" (frequency components).

・ Long-term measurement is realized by adopting the dual-comb down-conversion method in the reception system.

Measurement Principle of Microwave Reflectometer

2. Constructed an integrated plasma measurement system and demonstrated it on "Heliotron J"

・ Developed an integrated plasma measurement system from the microwave transmitter of the frequency comb to the transmission and reception system, and constructed it on the fusion plasma experimental device "Heliotron J".

・ Actual measurement results successfully achieved long-term measurement of frequency changes at up to 34 points corresponding to changes in plasma state.

Measurement device constructed on Heliotron J

Multi-point measurement results of frequency changes in plasma over time

34 frequency components (vertical axis) and the temporal changes observed for each frequency component (horizontal axis). Red indicates that the frequency changed in the positive direction relative to the incident frequency, and blue indicates a change in the negative direction relative to the incident frequency.

Role Allocation

Organization Name

Role

Mitsubishi Electric

Development of microwave transmission and reception devices, construction of measurement equipment for "Heliotron J"

Kyoto University

Generation of high-density plasma, elucidation of plasma physical phenomena

National Institute for Fusion Science

Development of the dual-comb down-conversion method, elucidation of plasma physical phenomena

Future Plans and Prospects

We aim to further advance the control technology using microwaves from frequency combs and construct more detailed plasma measurement systems. Furthermore, with a view to power generation demonstrations in the 2030s, we will also consider constructing systems with excellent environmental resistance for adoption in commercial reactors.

About Kyoto University

Kyoto University is one of the oldest research institutions in Japan and Asia. Since its founding in 1897, it has produced numerous Nobel laureates and recipients of other internationally acclaimed awards. It offers a wide range of curricula from humanities and social sciences to natural sciences for undergraduate and graduate students, supported by numerous research institutes, facilities, and administrative offices located throughout Japan and around the world. For more detailed information, please visit the following link: https://www.kyoto-u.ac.jp/ja

About National Institute for Fusion Science

NIFS is engaged in various research challenges necessary for realizing fusion energy in a usable form, including plasma physics, microscopic quantum processes, materials science, and the engineering technologies of the devices that constitute the system. As an inter-university research institute, it provides access to large-scale research facilities such as plasma confinement devices and supercomputers, as well as a variety of research equipment for joint use, and promotes collaborative research with universities and research institutions in Japan and abroad. Along with the advancement of fusion science, it promotes the formation of a broad scientific and technological foundation.

About Mitsubishi Electric Group

Under "Our Philosophy," the Mitsubishi Electric Group places sustainability at the core of its management and values the trust of stakeholders, including society, customers, shareholders, and employees. We pursue "profitability," "capital efficiency," and "growth," while continuously connecting with customers to create new value that solves social issues and strive for sustainable improvement of corporate value. With a history of over 100 years since its founding in 1921, the Group operates in businesses such as social systems, energy systems, defense and space systems, factory automation systems, automotive equipment, building systems, air conditioning and home appliances, digital innovation, and semiconductors/devices. With over 200 group companies worldwide and approximately 150,000 employees, consolidated sales for fiscal year 2025 were 5,894.7 billion yen. For more details, please visit our official website.

※1 As of June 29, 2026, according to research by Mitsubishi Electric, Kyoto University, and NIFS.

※2 Energy released when light atomic nuclei fuse to form different atomic nuclei, the energy that makes the sun shine.

※3 https://heliotronj.iae.kyoto-u.ac.jp/

※4 https://www8.cao.go.jp/cstp/fusion/index.html

※5 Microwaves in which numerous frequency components are arranged at equal intervals, like the teeth of a comb. Contains multiple frequency components simultaneously.

※6 A method that converts high-frequency signals into low-frequency signals that are easier to measure by combining two frequency comb signals with different intervals, enabling simultaneous acquisition of numerous frequency components.

※7 The number of measurement points depends on the plasma's electron density state and varies depending on discharge conditions.

※8 Europe's largest international conference on plasma physics (https://epsplasma2026.com/)

※9 The electron density at the boundary where microwaves are no longer able to penetrate further into the plasma and are reflected. Since it varies with the frequency of the microwaves, it is possible to understand the internal structure of the plasma by changing the frequency.

※10 A phenomenon where the frequency (pitch of sound, etc.) of sound or radio waves is observed to change when the source is moving.

Contact Information

Mitsubishi Electric Corporation, Advanced Technology R&D Center

8-1, Tsukaguchi-Honmachi 8-chome, Amagasaki, Hyogo 661-8661, Japan

FAX 06-6497-7285

https://www.MitsubishiElectric.co.jp/corporate/randd/inquiry/index_at.html

Kyoto University, Institute of Advanced Energy, Public Relations Office

5-1, Gokasho, Uji, Kyoto 611-0011, Japan

TEL 0774-38-3402 FAX 0774-38-3412

https://www.iae.kyoto-u.ac.jp/contactform/

National Institute for Fusion Science, Administration Department, General Affairs and Planning Division, External Cooperation Section

TEL 0572-58-2016

E-mail taigai-kakari@nifs.ac.jp