Development of three-color laser interferometer for high accuracy electron density measurement

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K14694
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 14020:Nuclear fusion-related
• Research Institution: National Institutes for Quantum Science and Technology
• Principal Investigator: Ohtani Yoshiaki 国立研究開発法人量子科学技術研究開発機構, 那珂研究所 先進プラズマ研究部, 主任研究員 (10805823)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 干渉計測 / レーザー計測 / プラズマ計測 / 磁場閉じ込め核融合

Outline of Final Research Achievements

In order to reduce a noise floor in the interferometer and measure the plasma in high accuracy, the three-color laser interferometer which is the improved one of the two-color laser interferometer has been developed. This interferometer consists of three one-color laser interferometers with coaxial laser beams, and be considered as three sets of a two-color laser interferometer. From the two sets of the two-color laser interferometer, the value consisting only of the noise floor can be assessed. The noise floor can be reduced by subtracting the value consisting only of the noise floor from the measurement value obtained with the other two-color laser interferometer.
In the demonstration, a noise floor reduction by 15%, and a 100-Hz noise reduction by 53% were achieved. The 100-Hz noise floor is caused by the vibration noise, which remains because of the non-coaxiality of the three beams.
This result is published in Review of Scientific Instruments.

Free Research Field

プラズマ計測

Academic Significance and Societal Importance of the Research Achievements

本研究により、３波長干渉計は磁場閉じ込め核融合プラズマの密度計測を高精度化することができることを示した。これまで２波長干渉計によって振動ノイズは除去されているものとして評価されてきたが、わずかな光軸のずれが密度計測の精度を悪化させることを明らかにした。また、本干渉計は振動ノイズ成分だけでなく、それ以外の周波数帯のノイズも低減しており、２波長干渉計よりも高精度に計測することが可能である。本成果は、詳細な物理研究のための計測器のみならず、将来的にプラズマの密度制御のための高精度モニタとして、核融合エネルギー研究に貢献できるものと思われる。