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Matsuoka, Seikichi*; Sugama, Hideo*; Idomura, Yasuhiro
Physics of Plasmas, 28(6), p.064501_1 - 064501_5, 2021/06
Times Cited Count：4 Percentile：40.28(Physics, Fluids & Plasmas)The improved model collision operator proposed by Sugama et al., which can recover the friction-flow relation of the linearized Landau collision operator, is newly implemented in a global full- f gyrokinetic simulation code, GT5D, and collisional transport simulations of a single ion species plasma in a tokamak are performed over the wide collisionality regime. The improved operator is verified to reproduce the theoretical collisional thermal diffusivity precisely in the high collisionality regime, where the friction-flow relation of higher accuracy is required than in the lower collisional regime. In addition, it is found in all collisionality regimes that the higher accuracy of the collisional thermal diffusivity and the parallel flow coefficient is obtained by the improved operator, demonstrating that collisional processes described by the linearized Landau collision operator is correctly retained.
Matsuoka, Seikichi; Idomura, Yasuhiro; Satake, Shinsuke*
Physics of Plasmas, 25(2), p.022510_1 - 022510_10, 2018/02
Times Cited Count：17 Percentile：73.90(Physics, Fluids & Plasmas)Global full-f gyrokinetic simulations, in which the gyrokinetic equation is solved based on the first principle without the scale separation with respect to the plasma distribution function, is attracting much attention in the plasma transport simulation studies. In this work, in order to apply a global full-f gyrokinetic simulation code GT5D to stellarator plasmas with complicated three-dimensional magnetic field configurations, we extend finite difference scheme of GT5D and develop a new interface code which incorporates the three-dimensional magnetic equilibria provided by a standard equilibrium code, VMEC. A series of benchmark calculations are carried out for the numerical verification of GT5D. It is successfully demonstrated that GT5D well reproduces results of a theoretical analysis and another global neoclassical transport code.
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.
Matsuoka, Seikichi; Idomura, Yasuhiro; Satake, Shinsuke*
Physics of Plasmas, 24(10), p.102522_1 - 102522_9, 2017/10
Times Cited Count：4 Percentile：21.22(Physics, Fluids & Plasmas)In axisymmetric tokamak plasmas, effects of three-dimensional non-axisymmetric magnetic field perturbations caused by error fields etc. have attracted much attention from the view point of the control of the plasma performance and instabilities. Recent studies pointed out that there exists qualitative discrepancy in predicting the collisional viscosity driven by the perturbation between a theoretical bounce-averaged model and a global kinetic simulation. Clarifying the cause of the discrepancy by understanding the underlying mechanism is a key issue to establish a reliable basis for the NTV predictions. In this work, we perform two different kinds of global kinetic simulations for the NTV. As a result, it is first demonstrated that the discrepancy arises owing to the following two mechanisms related to the global particle orbit; (1) the effective magnitude of the perturbation becomes weak due to the loss of the resonant orbit, and (2) the phase mixing along the orbit arises and generates fine scale structures, resulting the damping of the NTV.
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：11 Percentile：53.03(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 
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 drift is small and compared to the magnetic drift, can be mitigated in the ZOW model.
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：11.38(Physics, Fluids & Plasmas)A drift-kinetic 
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.
Idomura, Yasuhiro; Asahi, Yuichi; Ina, Takuya; Matsuoka, Seikichi
Proceedings of 24th International Congress of Theoretical and Applied Mechanics (ICTAM 2016), p.3106 - 3107, 2016/08
Turbulent transport in fusion plasmas is one of key issues in ITER. To address this issue via the five dimensional (5D) gyrokinetic model, a novel computing technique is developed, and strong scaling of the Gyrokinetic Toroidal 5D Eulerian code GT5D is improved up to 
million cores on the K-computer. The computing technique consists of multi-dimensional/multi-layer domain decomposition, overlap of communication and computation, and optimization of computing kernels for multi-core CPUs. The computing power enabled us to study ITER relevant issues such as the plasma size scaling of turbulent transport. Towards the next generation burning plasma turbulence simulations, the physics model is extended including kinetic electrons and multi-species ions, and computing kernels are further optimized for the latest many-core architectures.
Sugama, Hideo*; Matsuoka, Seikichi; Satake, Shinsuke*; Kanno, Ryutaro*
Physics of Plasmas, 23(4), p.042502_1 - 042502_11, 2016/04
Times Cited Count：7 Percentile：36.76(Physics, Fluids & Plasmas)A novel radially local approximation of the drift kinetic equation is presented. The new drift kinetic equation that includes both 
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.
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.
Matsuoka, Seikichi*; Satake, Shinsuke*; Idomura, Yasuhiro; Imamura, Toshiyuki*
Proceedings of Joint International Conference on Mathematics and Computation, Supercomputing in Nuclear Applications and the Monte Carlo Method (M&C + SNA + MC 2015) (CD-ROM), 13 Pages, 2015/04
The quality and performance of a parallel pseudo-random number generator (PRNG), KMATH_RANDOM, are investigated using a Monte Carlo particle simulation code for the plasma transport. The library is based on Mersenne Twister with jump routines and provides a numerical tool which is suitable and easy-to-use on massively parallel supercomputers such as K-computer. The library enables the particle code to increase the parallelization up to several thousand processes without loosing the quality and performance of the PRNG. As a result, the particle code can use large amounts of random numbers, which results in removing unphysical phenomena caused by a numerical noise.
flows in helical plasmasWatanabe, Tomohiko*; Nunami, Masanori*; Sugama, Hideo*; Satake, Shinsuke*; Matsuoka, Seikichi*; Ishizawa, Akihiro*; Maeyama, Shinya; Tanaka, Kenji*
Proceedings of 24th IAEA Fusion Energy Conference (FEC 2012) (CD-ROM), 8 Pages, 2012/10
Matsuoka, Seikichi; Idomura, Yasuhiro; Satake, Shinsuke*
no journal, ,
Effects of non-axisymmetric magnetic field perturbations on plasma transport in tokamaks have attracted much attention from the view point of the control of the plasma performance and instabilities. Recent studies pointed out that there exists qualitative discrepancy in predicting the collisional viscosity driven by the perturbation between a theoretical bounce-averaged model and a global kinetic simulation. Clarifying the cause of the discrepancy by understanding the underlying mechanism is a key issue to establish a reliable basis for the NTV predictions. In this work, we perform two different kinds of global kinetic simulations for the NTV. As a result, it is first demonstrated that the discrepancy arises owing to the following two mechanisms; (1) the effective magnitude of the perturbation becomes weak due to the finite orbit width of the global particle orbit, and (2) the velocity space structures are damped by the phase mixing along the global particle orbit.
Idomura, Yasuhiro; Matsuoka, Seikichi; Ina, Takuya; Garbet, X.*; Brunner, S.*; Villard, L.*; Kawai, Chika*
no journal, ,
This talk reviews outcomes from GT5DISO projects, which was conducted for FY2014-2016. In this project, isotope effects on turbulent transport have been studied using the gyrokinetic toroidal five dimensional full-f Eulerian code GT5D. In FY2014, it was shown that the ion temperature gradient driven (ITG) turbulence with adiabatic electrons does not show isotope effects, and the trapped electron mode (TEM) driven by kinetic trapped electrons is essential for this issue. In FY2015, a new hybrid kinetic electron model was developed in GT5D, and its verification tests for ITG-TEM turbulence simulations were conducted. In FY2016, the kinetic electron model was validated against electron heating modulation experiments, in which the TEM turbulence plays key roles in particle and momentum transport. Finally, we performed isotope scan of ITG-TEM turbulence simulations, which tend to indicate difference of confinement between hydrogen and deuterium plasmas.
Matsuoka, Seikichi; Idomura, Yasuhiro; Satake, Shinsuke*
no journal, ,
Effects of non-axisymmetric magnetic field perturbations on plasma transport in tokamaks have attracted much attention from the view point of the control of the plasma performance and instabilities. Recent studies pointed out that there exists qualitative discrepancy in predicting the collisional viscosity driven by the perturbation between a theoretical bounce-averaged model and a global kinetic simulation. Clarifying the cause of the discrepancy is a key issue to establish a reliable basis for the NTV predictions. In this work, we perform two types of global kinetic simulations for the NTV to investigate the discrepancy from the theoretical model. As a result, it is first demonstrated that the discrepancy arises owing to the following two mechanisms; (1) resonant structures predicted in the bounce-averaged model become weak due to global particle orbit width effects, and (2) the velocity space structures are damped by the phase mixing.
Matsuoka, Seikichi; Idomura, Yasuhiro; Satake, Shinsuke*
no journal, ,
Recently, full-f simulations, in which the gyrokinetic equation is solved based on the first principle to obtain the time development of the total plasma distribution function, attracted much attention in the plasma transport study. Rich physics has been revealed by the simulations in axisymmetric tokamak plasmas such as JT-60 and ITER. However, no such full-f gyrokinetic simulations in three-dimensional magnetic field equilibria such as stellarators and/or helical devices have been reported so far due to their complicated magnetic field geometries which requires more computational resources. In this work, we extend a full-f gyrokinetic simulation code, GT5D, to treat three-dimensional magnetic equilibria by modifying its coordinate system, and develop a new interface between GT5D and VMEC, where VMEC is a widely used numerical tool to construct a three-dimensional magnetic equilibria. In the presentation, we give a presentation of the current status of the code development, numerical scheme used in the code, and simulation results.
Matsuoka, Seikichi; Idomura, Yasuhiro; Satake, Shinsuke*
no journal, ,
Global full-f gyrokinetic simulations, in which the gyrokinetic equation is solved based on the first principle without the scale separation with respect to the plasma distribution function, is attracting much attention in the plasma transport study. The existing global full-f gyrokinetic simulation codes are developed with the aim to explore the transport physics in axisymmetric tokamak plasmas, in which the magnetic field is two-dimensional, and no global full-f gyrokinetic simulation study in stellarator plasmas, where the magnetic field has complicated three-dimensional structures, has been reported so far. In this work, we extend a global full-f gyrokinetic simulation code, GT5D, to incorporate three-dimensional magnetic equilibria by extending the numerical scheme in GT5D. The extended version of GT5D is verified against the zonal flow damping, the collisional (neoclassical) transport, and the ambipolar radial electric field by comparing against an analytical theory and another neoclassical code.
Matsuoka, Seikichi; Idomura, Yasuhiro; Satake, Shinsuke*
no journal, ,
Global full-f gyrokinetic simulations, in which the gyrokinetic equation is solved based on the first principle without the scale separation with respect to the plasma distribution function, attracted much attention in the plasma transport study. Rich physics has been revealed by the simulations in axisymmetric tokamak plasmas such as JT-60 and ITER. However, no full-f simulations in three-dimensional magnetic field equilibria such as stellarators have been reported so far due to their complicated magnetic field geometries. In this work, we extend a full-f gyrokinetic simulation code, GT5D, to treat three-dimensional magnetic equilibria. A new interface code between GT5D and a 3D equilibrium code, VMEC, are developed, in which the geometry and the magnetic field provided by VMEC code is incorporated into GT5D. It is demonstrated that the neoclassical transport physics of GT5D can successfully reproduce results of another neoclassical transport code and a theory.
Matsuoka, Seikichi; Idomura, Yasuhiro; Satake, Shinsuke*
no journal, ,
Global full-f gyrokinetic simulations, in which the gyrokinetic equation is solved based on the first principle without the scale separation with respect to the plasma distribution function, is attracting much attention in the plasma transport study. However, global full-f gyrokinetic simulation studies in three-dimensional plasmas have been reported so far, since the existing global full-f gyrokinetic simulation codes are developed with the aim to explore the transport physics in axisymmetric tokamak plasmas. In this work, we extend a global full-f gyrokinetic simulation code, GT5D, to treat three-dimensional magnetic equilibria by constructing a new coordinate system. A new interface code between GT5D and a 3D equilibrium code, VMEC, are developed, in which outputs provided by VMEC code is incorporated into GT5D. The extended version of GT5D is verified against the collisional (neoclassical) transport by comparing the transport to another neoclassical code and an analytical theory.
Idomura, Yasuhiro; Ina, Takuya*; Obrejan, K.; Asahi, Yuichi*; Matsuoka, Seikichi*; Imamura, Toshiyuki*
no journal, ,
Under the post-K project, we have developed computing techniques of the Gyrokinetic Toroidal 5D full-f Eulerian code GT5D towards the next generation computing platforms based on many core processors. We discuss computational challenges related to complicated intra-processor memory hierarchy and limited inter-node communication performance compared with accelerated computation. The former issue is addressed by optimizing data access patterns of a stencil kernel on each many core architecture, and high performance gains are obtained. The latter issue is resolved by using advanced communication avoiding Krylov methods, which enables an order of magnitude reduction of collective communications and improves arithmetic intensity of main computing kernels. By applying these novel computing techniques, the performance of GT5D is dramatically improved on the latest many core platforms, and excellent strong scaling up to the full system size of the Oakforest-PACS (8,192 KNLs) is achieved.
Matsuoka, Seikichi; Idomura, Yasuhiro; Satake, Shinsuke*
no journal, ,
Global full-f gyrokinetic simulations, in which the gyrokinetic equation is solved based on the first principle without the scale separation with respect to the plasma distribution function, is attracting much attention in the plasma transport study. In this study, we extend a global full-f gyrokinetic simulation code, GT5D, to treat stellarator plasmas with complicated three-dimensiuonal magnetic field equilibria by developing a new interface code which incorporates the three-dimensional equilibria provided by a standard equilibrium code, VMEC, and by extending a finite difference scheme in GT5D. In order to obtain numerical verification of GT5D, we perform a series of benchmark simulations. It is successfully confirmed that GT5D well reproduces results of a theoretical analysis and another neoclassical transport code.
