| Co-Investigator(Kenkyū-buntansha) |
FUJISAWA Akihide National Institute for Fusion Science, Associate professor, 大型ヘリカル研究部, 助教授 (60222262)
IDA Katsumi National Institute for Fusion Science, Professor, 大型ヘリカル研究部, 教授 (00184599)
SANUKI Heiji National Institute for Fusion Science, Associate professor, 大型ヘリカル研究部, 助教授 (80109355)
ITOH Sanae-I Institute for Applied Mechanics, Kyushu University, Professor, 応用力学研究所, 教授 (70127611)
TODA Shinichiro National Institute for Fusion Science, Research associate, 大型ヘリカル研究部, 助手 (60332186)
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| Research Abstract |
In this research project, a possibility of improved confinement in helical plasmas is investigated, putting an emphasis on the mechanism of "electric field bifurcation and turbulence suppression". In addition, a proposal of experimental test by use of CHS device is examined.
In the analysis, we first study the condition that the electric field interface is realized in helical plasmas. The electric field interface, across which the domains with different electric field polarity contact each other, is associated with the strong gradient of radial electric field. This gradient of electric field could reach the level where the microscopic plasma turbulence could be suppressed. This structure has been predicted to exist, and the issue is to investigate whether it is self-sustained in a stationary state and whether such a stationary state is easily accessible or not.
These problems were studied in this project, by exploring a theoretical model together with the transport simulation code which includes the presence of interface. Theoretical model of microscopic turbulence is combined with the study of interface, and a threshold condition is derived. The self-sustaining mechanism is verified to work in heliotron/torsatron type configurations, and the accessibility to such a state is analyzed in the space of controlling parameters. A phase diagram was obtained. Based on the theoretical framework, experimental studies were performed. It was shown that the electric field interface is possible to occur in CHS so as to suppress the microscopic plasma turbulence. The internal transport barrier for electron energy was also found in W7-AS and LHD devices, confirming the validity of the theoretical model.
Through this project, theory for plasma turbulence, transition and structure formation has been progressed substantially.
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