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Journal Articles

Electron heat diffusivity in radially-bounded ergodic region of toroidal plasma

Kanno, Ryutaro*; Nunami, Masanori*; Satake, Shinsuke*; Matsuoka, Seikichi; Takamaru, Hisanori*

Nuclear Fusion, 58(1), p.016033_1 - 016033_7, 2018/01

 Times Cited Count:0 Percentile:0.01(Physics, Fluids & Plasmas)

The electron heat transport in a torus plasma which involves a radially-bounded ergodic region, where flux surfaces are partially destroyed by perturbative magnetic fields, is studied. In this paper, we have demonstrated that the radial heat conduction by the particles' parallel motion is reduced by trapped particles.

Journal Articles

Benchmark of the local drift-kinetic models for neoclassical transport simulation in helical plasmas

Huang, B.*; Satake, Shinsuke*; Kanno, Ryutaro*; Sugama, Hideo*; Matsuoka, Seikichi

Physics of Plasmas, 24(2), p.022503_1 - 022503_19, 2017/02

 Times Cited Count:9 Percentile:56.2(Physics, Fluids & Plasmas)

The drift kinetic equation describes the collisional (neoclassical) transport in plasmas. Recently, a novel radially-local approximation of the drift kinetic equation, which is called the zero orbit width (ZOW) model, is proposed. In this work, as a numerical verification of the neoclassical transport based on the ZOW model, we perform a series of benchmarks of the neoclassical transport and the parallel flow in three helical magnetic configurations using various types of radially-local approximation models including the ZOW model. We found that the neoclassical transport of the ZOW model can reproduce that based on the other models when the radial electric field and thus the $$E times B$$ drift is large. Also, it is demonstrated that an unphysical large radial transport, which arises in the neoclassical transport of the other models when the $$E times B$$ drift is small and compared to the magnetic drift, can be mitigated in the ZOW model.

Journal Articles

Development of a drift-kinetic simulation code for estimating collisional transport affected by RMPs and radial electric field

Kanno, Ryutaro*; Nunami, Masanori*; Satake, Shinsuke*; Matsuoka, Seikichi; Takamaru, Hisanori*

Contributions to Plasma Physics, 56(6-8), p.592 - 597, 2016/08

 Times Cited Count:2 Percentile:13.82(Physics, Fluids & Plasmas)

A drift-kinetic $$delta f$$ simulation code is developed for estimating collisional transport in quasi-steady state of toroidal plasma affected by resonant magnetic perturbations and radial electric field. In this paper, validity of the code is confirmed through several test calculations. It is found that radial electron flux is reduced by positive radial-electric field, although radial diffusion of electron is strongly affected by chaotic field-lines under an assumption of zero electric field.

Journal Articles

Radially local approximation of the drift kinetic equation

Sugama, Hideo*; Matsuoka, Seikichi; Satake, Shinsuke*; Kanno, Ryutaro*

Physics of Plasmas, 23(4), p.042502_1 - 042502_11, 2016/04

 Times Cited Count:4 Percentile:26.04(Physics, Fluids & Plasmas)

A novel radially local approximation of the drift kinetic equation is presented. The new drift kinetic equation that includes both $$rm E times B$$ and tangential magnetic drift terms is written in the conservative form and it has favorable properties for numerical simulation that any additional terms for particle and energy sources are unnecessary for obtaining stationary solutions under the radially local approximation. These solutions satisfy the intrinsic ambipolarity condition for neoclassical particle fluxes in the presence of quasisymmetry of the magnetic field strength. Also, another radially local drift kinetic equation is presented, from which the positive definiteness of entropy production due to neoclassical transport and Onsager symmetry of neoclassical transport coefficients are derived while it sacrifices the ambipolarity condition for neoclassical particle fluxes in axisymmetric and quasi-symmetric systems.

Journal Articles

Progress report of Japanese simulation research projects using the high-performance computer system Helios in the International Fusion Energy Research Centre

Ishizawa, Akihiro*; Idomura, Yasuhiro; Imadera, Kenji*; Kasuya, Naohiro*; Kanno, Ryutaro*; Satake, Shinsuke*; Tatsuno, Tomoya*; Nakata, Motoki*; Nunami, Masanori*; Maeyama, Shinya*; et al.

Purazuma, Kaku Yugo Gakkai-Shi, 92(3), p.157 - 210, 2016/03

The high-performance computer system Helios which is located at The Computational Simulation Centre (CSC) in The International Fusion Energy Research Centre (IFERC) started its operation in January 2012 under the Broader Approach (BA) agreement between Japan and the EU. The Helios system has been used for magnetised fusion related simulation studies in the EU and Japan and has kept high average usage rate. As a result, the Helios system has contributed to many research products in a wide range of research areas from core plasma physics to reactor material and reactor engineering. This project review gives a short catalogue of domestic simulation research projects. First, we outline the IFERC-CSC project. After that, shown are objectives of the research projects, numerical schemes used in simulation codes, obtained results and necessary computations in future.

Journal Articles

Spin-orbital short-range order on a honeycomb-based lattice

Nakatsuji, Satoru*; Kuga, Kentaro*; Kimura, Kenta*; Satake, Ryuta*; Katayama, Naoyuki*; Nishibori, Eiji*; Sawa, Hiroshi*; Ishii, Rieko*; Hagiwara, Masayuki*; Bridges, F.*; et al.

Science, 336(6081), p.559 - 563, 2012/05

 Times Cited Count:108 Percentile:95.76(Multidisciplinary Sciences)

Frustrated magnetic materials can remain disordered to the lowest temperatures. Such is the case for Ba$$_3$$CuSb$$_2$$O$$_9$$, which is magnetically anisotropic at the atomic scale but curiously isotropic on mesoscopic length and time scales. We find that the frustration on the triangular lattice is imprinted in a nanostructured honeycomb lattice of Cu$$^{2+}$$ ions that resists a coherent static Jahn-Teller distortion. The resulting two-dimensional random-bond spin-1/2 system on the honeycomb lattice has a broad spectrum of spin-dimer like excitations and low-energy spin degrees of freedom that retain.

Oral presentation

Neoclassical toroidal viscosity calculation method by a particle code based on a local approximation drift-kinetic model

Satake, Shinsuke*; Sugama, Hideo*; Kanno, Ryutaro*; Matsuoka, Seikichi; Idomura, Yasuhiro; Huang, B.*

no journal, , 

The accurate evaluation of the neoclassical toroidal viscosity (NTV) driven by non-axisymmetric external perturbation and/or error field in a tokamak plasma is an important topic in the fusion research, since it can make an influence on the plasma toroidal rotation. This has been widely done so far by analytically and numerically solving the bounce-averaged drift-kinetic equation based on the so-called local approximation, under which the radial drift the particle is neglected. Recently, we have developed two global kinetic simulations based on $$delta f$$ and full-$$f$$ models respectively. It has been shown that the so-called Superbanana-Plateau collisionality regime expected in the bounce-averaged theory, in which the NTV is independent of the collisionality, is not observed in both global kinetic simulations. On the other hand, however, the two global simulations reproduce the similar collisionality dependencies of the NTV. With regard to the discrepancy of the theory and the global kinetic simulations, it has been recently pointed out that the effect of the magnetic field shear on the toroidal precession drift is not retained in the theory. In this study, we perform particle simulations, which is based on the local approximation, for the NTV. We discuss the cause of the discrepancy of the difference between the bounce-averaged local theory and the global kinetic simulations by investigating the effect of shear on the toroidal precession drift using the local particle simulations.

Oral presentation

Comparison of bootstrap current calculation in helical plasmas among different types of approximations in drift-kinetic equation

Huang, B.*; Satake, Shinsuke*; Kanno, Ryutaro*; Matsuoka, Seikichi

no journal, , 

The bootstrap current, or the parallel flow in a toroidal plasma is described by the neoclassical transport theory. In recent studies, it was pointed out that numerical models of the radially-local neoclassical transport, in which the radial drift of particles is entirely neglected, can be classified according to approximations used in the models. In this work, we perform a series of benchmarks of the parallel flow for the LHD, HSX, and W7-X by using three types of the local neoclassical transport simulations models. It is shown that the magnetic drift tangential to a flux surface significantly changes the parallel flow when the radial electric field is weak in a low-collisional LHD plasma. We also find that the effect of the tangential drift becomes small in other magnetic configurations of HSX and W7-X.

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