Kyushu University [Naohiro Kasuya (Professor) Research Institute for Applied Mechanics, Division of Nuclear Fusion Dynamics]

Main subject is numerical simulation of structural formation in magnetic confinement fusion plasmas. We are developing the turbulence diagnostic simulator research, which aims to understand what kind of turbulent structures are identified with specific experimental diagnostics by using numerical simulations. We also carry out drift wave turbulence simulations in linear devices and dynamical response simulations in toroidal plasmas.

Research

Research Interests

Numerical simulation of turbulent structural formation in magnetized plasmas
keyword : simulation, turbulence, structural formation, numerical diagnostic
2009.04～2024.03.
Research on electro-static and –magnetic instabilities in magnetized plasmas
keyword : magnetized plasma, instability, mode structure, growth rate
2012.05～2024.03.
Research on particle and heat transport in burning plasmas
keyword : transport, impurity, integrated simulation, burning plasma
2017.04～2024.03.
Numerical diagnostic of plasma fluctuation data
keyword : numerical diagnostic, simulation, data, fluctuation
2011.04～2024.03.

Academic Activities

Reports

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1.	N. Kasuya, T. Ido and A. Shimizu, Diagnostic Simulator and the Future of Turbulent Diagnostics, J. Plasma Fusion Res. 88 (2012) 322.

Papers

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1.	N. Kasuya, M. Nunami, K. Tanaka, and M. Yagi, Numerical diagnostics of fluctuation spectrum in 3D magnetic configurations, NUCLEAR FUSION, 10.1088/1741-4326/aad784, 58, 10, 2018.10, 原著論文"Numerical diagnostics of fluctuation spectrum in 3D magnetic configurations (3次元磁場配位における揺動スペクトルの数値診断)"では、3次元的磁場配位を持つヘリカルプラズマで計測を模した数値診断を行い、計測や解析手法によって観測される揺動スペクトルにどれほどの空間精度が得られるかを評価した結果を報告した。ジャイロ運動論モデルを用いて計算した3次元実配位下でのイオン温度勾配乱流データに対して、位相コントラスト法での密度揺動計測で問題になる計測視線線積分、統計的解析手法の効果について検討し、実験結果との比較を行った。.
2.	Naohiro Kasuya, Makoto Sasaki, Satoshi Abe, Masatoshi Yagi, On the radial eigenmode structure of drift wave instability with inhomogeneous damping in cylindrical plasmas, Journal of the Physical Society of Japan, 10.7566/JPSJ.87.024501, 87, 2, 2018.01, Plasma flows can be driven by turbulent stresses from excited modes in magnetized plasmas. Our recent numerical simulation of resistive drift wave turbulence in a linear device has shown that the radial inhomogeneity of the neutral density affects azimuthal flow generation by changing the phase structure of the most unstable eigenmodes. Eigenmode analyses show that the mode structure has a complex Bessel-type function shape in the central region of the plasma, and the imaginary part arises from the radial inhomogeneity of the damping term caused by ion-neutral collisions. The amplitude of turbulent stress is proportional to the inhomogeneity under a marginally stable condition. Global structural formation is an important factor for determining the plasma turbulent state, and this result clearly shows that several kinds of radial background distributions, the plasma and neutral densities in this case, can influence the global structures..
3.	Naohiro Kasuya, Satoru Sugita, Shigeru Inagaki, Kimitaka Itoh, Masatoshi Yagi, Sanae-I. Itoh, Simulation study of hysteresis in the gradient-flux relation in toroidal plasma turbulence, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/57/4/044010, 57, 4, 2015.04.
4.	Naohiro Kasuya, Satoru Sugita, Shigeru Inagaki, Kimitaka Itoh, Masatoshi Yagi, Sanae-I. Itoh, On violation of local closure of transport relation in high-temperature magnetized plasmas, Physics of Plasmas, 2014.11.
5.	Naohiro Kasuya, Satoru Sugita, Makoto Sasaki, Shigeru Inagaki, Masatoshi Yagi, Kimitaka Itoh, Sanae-I. Itoh, Evaluation of Spatial Variation of Nonlinear Energy Transfer by Use of Turbulence Diagnostic Simulator, Plasma and Fusion Research, DOI: 10.1585/pfr.8.2403070, 8, 2403070-1-2403070-5, 2013.06, Turbulence Diagnostic Simulator is an assembly of simulation codes to clarify the formation mechanism of turbulent structures by numerical diagnostics in magnetically confined plasmas. Global simulations are carried out using a reduced MHD model of drift-interchange mode in helical plasmas, and time series data of 3-D fluctuation fields are produced. It includes localized modes in their rational surfaces, and broad modes spread in the radial direction. Magnitudes of nonlinear couplings from the convective derivative are evaluated in the nonlinear saturated states. The radial profile shows that there exist strong mode excitation near the center, various modes and nonlinear couplings with higher m modes in the middle radius, small number of propagating modes near the edge, which contribute to the pressure profile modification. For the detection of the different features, combination of several diagnostics is necessary..
6.	N. Kasuya, S. Nishimura, M. Yagi, K. Itoh, and S.-I. Itoh, Heavy Ion Beam Probe Measurement in Turbulence Diagnostic Simulator, Plasma Science and Technology, 13, 3, 326, 2011.03, A numerical measurement module simulating a heavy ion beam probe was developed, and numerical measurements of electrostatic potential and density fluctuations are carried out for 3-D turbulent data generated by a global simulation of drift-interchange mode turbulence in helical plasmas. The deviation between measured and local values is estimated. It is found that the characteristic structures can be detected in spite of the screening effect due to the finite spatial resolution..
7.	N. Kasuya, M. Yagi, K. Itoh, and S.-I. Itoh, Selective Formation of Turbulent Structures in Magnetized Cylindrical Plasmas, Physics of Plasmas, 10.1063/1.2912461, 15, 5, 052302, 2008.05, The mechanism of nonlinear structural formation has been studied with a three-field reduced fluid model, which is extended to describe the resistive drift wave turbulence in magnetized cylindrical plasmas. In this model, ion-neutral collisions strongly stabilize the resistive drift wave, and the formed structure depends on the collision frequency. If the collision frequency is small, modulational coupling of unstable modes generates a zonal flow. On the other hand, if the collision frequency is large, a streamer, which is a localized vortex in the azimuthal direction, is formed. The structure is generated by nonlinear wave coupling and is sustained for a much longer duration than the drift wave oscillation period. This is a minimal model for analyzing the turbulent structural formation mechanism by mode coupling in cylindrical plasmas, and the competitive nature of structural formation is revealed. These turbulent structures affect particle transport..
8.	Naohiro Kasuya, K. Itoh, Two-dimensional structure and particle pinch in tokamak H mode, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.94.195002, 94, 19, 2005.05.
9.	Naohiro Kasuya, K. Itoh, Y. Takase, Effect of electrode biasing on the radial electric field structure bifurcation in tokamak plasmas, NUCLEAR FUSION, 43, 4, 244-249, 2003.04.

Presentations

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1.	糟谷直宏, Global Structure and Its Diagnostic Simulation in Magnetized Plasma, 20th International Congress on Plasma Physics, 2022.11, 招待講演"Global Structure and Its Diagnostic Simulation in Magnetized Plasmas (磁化プラズマにおける巨視的構造とその診断シミュレーション)"では、核融合プラズマの輸送現象理解に重要な3次元的揺動構造を統合的に診断するプラットフォームiTDS研究の成果を報告した。これは我々が新たに開発したもので、トカマクをはじめとする様々な磁場配位プラズマに対する3次元シミュレーションデータに対して、複数の計測器を模擬した物理量の抽出を行い、揺動構造形成の効果を定量化できるものである。直線、トカマク、ヘリカル装置の揺動ダイナミクスに対する計測器信号模擬結果を提示した。.
2.	N. Kasuya, M. Nunami, K. Tanaka, C.A. Michael, S. Toda, M. Yagi, Numerical Diagnostic to Investigate Poloidal Asymmetry in Three-Dimensional Magnetic Configurations, 27th IAEA Fusion Energy Conference, 2018.10.
3.	N. Kasuya, M. Nunami K. Tanaka, M. Yagi, Fluctuation Spectrum Analysis Using Turbulence Simulation Data in 3-D Magnetic Configuration, 21st International Stellarator-Heliotron Workshop, 2017.10.
4.	糟谷直宏, 沼波政倫, 矢木雅敏, Numerical Diagnostics of Turbulent Transport in Three-Dimensional Magnetic Configurations, 25th IAEA Fusion Energy Conference, 2016.10.
5.	Naohiro Kasuya, Makoto Sasaki, Shigeru Inagaki, Kimitaka Itoh, Masatoshi Yagi, Sanae-I. Itoh, Numerical Diagnostics of Non-Diffusive Transport Process by Use of Turbulence Diagnostic Simulator, 25th IAEA Fusion Energy Conference, 2014.10.
6.	Naohiro Kasuya, Satoru Sugita, Shigeru Inagaki, Kimitaka Itoh, Masatoshi Yagi, Sanae-I. Itoh, Simulation Study of Hysteresis in the Flux-Gradient Relation in Turbulent Transport, 17th International Congress on Plasma Physics, 2014.09.
7.	Naohiro Kasuya, Makoto Sasaki, Shigeru Inagaki, Kimitaka Itoh, Masatoshi Yagi, Sanae-I. Itoh, Hysteresis and Nonlinearly Excited Mode Structures in Turbulence Simulation of a Toroidal Plasma, 4th APTWG International Workshop, 2014.06.
8.	Naohiro Kasuya, Satoru Sugita, Shigeru Inagaki, Makoto Sasaki, Kimitaka Itoh, Masatoshi Yagi, Sanae-I. Itoh, Identification of Dynamical Response Mechanism in a Turbulent Simulation with Source Modulation, 14th Int. Workshop on H-mode Physics and Transport Barriers, 2013.10.

Membership in Academic Society

Physical Society of Japan
Japan Society of Plasma Science and Nuclear Fusion Research

Educational

Educational Activities

I am promoting the education for numerical simulations of fusion plasmas in IGSES, especially putting emphasis on the development of new methods to accelerate the collaboration to experimental researches. The examples of the topic are plasma turbulence simulations, numerical analyses of turbulence field data and development of the integrated code to simulate burning fusion plasmas.

Social

Professional and Outreach Activities

As the outreach activities, I have been carrying out educational activities of nuclear fusion researches through special lectures at public lectures and technical colleges..

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