Project/Area Number  07680547 
Research Category 
GrantinAid for Scientific Research (C)

Section  一般 
Research Field 
Nuclear fusion studies

Research Institution  National Institute for Fusion Science 
Principal Investigator 
KOMORI Akio National Institute for Fusion Science, Department of Large Helical Device Project, Associate Professor, 大型ヘリカル研究部, 助教授 (50143011)

CoInvestigator(Kenkyūbuntansha) 
SUZUKI Hajime National Institute for Fusion Science, Department of Large Helical Device Projec, 大型ヘリカル研究部, 助手 (20260044)
WATANABE Tsuguhiro National Institute for Fusion Science, Department of Large Helical Device Projec, 大型ヘリカル研究部, 教授 (70023728)

Project Fiscal Year 
1995 – 1996

Project Status 
Completed(Fiscal Year 1996)

Budget Amount *help 
¥2,200,000 (Direct Cost : ¥2,200,000)
Fiscal Year 1996 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 1995 : ¥1,400,000 (Direct Cost : ¥1,400,000)

Keywords  chaos / edge plasma / broadband turbulence / Compact Helical System / correlation dimension / the Lyapunov exponent / wavelet analysis / カオス / 周辺プラズマ / 広帯域不安定性 / コンパクトヘリカルシステム / 相関次元 / リヤプノフ指数 / ウェーブレット変換 
Research Abstract 
Aims of this study are understanding of edge plasma turbulence characterized by a broadband frequency spectrum in the Compact Helical System (CHS) from the chaotic point of view, so that the relation between plasma confinement and turbulent structure in the edge plasma will be better understood. The accurate largest Lyapunov exponent must be calculated for this purpose, which needs a long time series because it is expected to be relatively large in the edge plasma. Thus we have completed a data acquisition system which yields the time series of 1M data points, and tested it on CHS.We have also analyzed the spatial structure of the turbulence by using wavelet analysis. This technique is suitable for the analysis of data records containing pulses or shortlived events, because it is avoidable to average out these temporally localized occurrences by examining large sections of the data record. The Lyapunov exponent is calculated by the algorithm that is easy to implement and has less limitation even for high dimensional attractors. We have tested our implementation of the algorithm by analyzing time series from mathematical systems with known attractors, and have obtained the already tabulated values for the correlation dimension and largest Lyapunov exponent. Our use of 16K data points, obtained with a thermal neutral lithium beam of 1cm diameter with an eightchannel optical detection system, has allowed us to measure the structure for correlation dimensions up to12, and the fractal dimensions of 59 and the positive Lyapunov exponent have been obtained. Thus the broadband turbulence in CHS is essentially determined by relatively small number of variables, and the chaos observed is deterministic and the attractor is strange. The existence of a nonlinear dispersion relation of the turbulence is also suggested by wavelet analysis.
