Full- gyrokinetic simulations of ohmic L-mode plasmas in linear and saturated ohmic confinement regimes

Idomura, Yasuhiro; Dif-Pradalier, G.*; Garbet, X.*; Sarazin, Y.*; Tore Supra Teams*

Physics of Plasmas, 30(4), p.042508_1 - 042508_18, 2023/04

https://doi.org/10.1063/5.0127346

Two time slices in linear and saturated ohmic confinement (LOC and SOC) regimes in a Tore Supra ohmic L-mode discharge are analyzed using nonlinear global full- gyrokinetic simulations, and qualitative features of the LOC-SOC transition are reproduced. The exhaust of carbon impurity ions is caused by fast ion mixing, which is driven by the toroidal field stress. The intrinsic rotation develops in the opposite direction between the LOC and SOC phases, which is characterized by the different features of the mode asymmetry between trapped electron modes in the LOC phase and ion temperature gradient driven modes in the SOC phase, leading to the change of the profile shear stress. The energy fluxes of electrons and deuterium ions are dominant in the LOC and SOC phases, respectively, and the ratio of the energy confinement time between two phases agree with the experimental value.

Dynamics of enhanced neoclassical particle transport of tracer impurity ions in ion temperature gradient driven turbulence

Idomura, Yasuhiro; Obrejan, K.*; Asahi, Yuichi; Honda, Mitsuru*

Physics of Plasmas, 28(1), p.012501_1 - 012501_11, 2021/01

https://doi.org/10.1063/5.0027484

Tracer impurity transport in ion temperature gradient driven (ITG) turbulence is investigated using a global full- gyrokinetic simulation including kinetic electrons, bulk ions, and low to medium tracer impurities, where is the charge number. It is found that in addition to turbulent particle transport, enhanced neoclassical particle transport due to a new synergy effect between turbulent and neoclassical transports makes a significant contribution to tracer impurity transport. Bursty excitation of the ITG mode generates non-ambipolar turbulent particle fluxes of electrons and bulk ions, leading to a fast growth of the radial electric field following the ambipolar condition. The divergence of flows compresses up-down asymmetric density perturbations, which are subject to transport induced by the magnetic drift. The enhanced neoclassical particle transport depends on the ion mass, because the magnitude of up-down asymmetric density perturbation is determined by a competition between the compression effect and the return current given by the parallel streaming motion. This mechanism does not work for the temperature, and thus, selectively enhances only particle transport.

Self-organization of zonal flows and isotropic eddies in toroidal electron temperature gradient driven turbulence

Kawai, Chika*; Idomura, Yasuhiro; Ogawa, Yuichi*; Yamada, Hiroshi*

Physics of Plasmas, 27(8), p.082302_1 - 082302_11, 2020/08

https://doi.org/10.1063/5.0015565

Self-organization in the toroidal electron temperature gradient driven (ETG) turbulence is investigated based on a global gyrokinetic model in a weak magnetic shear configuration. Because of global profile effects, toroidal ETG modes with higher toroidal mode number n are excited at the outer magnetic surfaces, leading to strong linear wave dispersion. The resulting anisotropic wave turbulence boundary and the inverse energy cascade generate the self-organization of zonal flows, which is the unique mechanism in the global gyrokinetic model. The self-organization is confirmed both in the decaying turbulence initialized by random noises and in the toroidal ETG turbulence. It is also shown that the self-organization process generates zonal flows and isotropic eddies depending on a criterion parameter, which is determined by the ion to electron temperature ratio and the turbulence intensity.

Synergy of turbulent and neoclassical transport through poloidal convective cells

Asahi, Yuichi*; Grandgirard, V.*; Sarazin, Y.*; Donnel, P.*; Garbet, X.*; Idomura, Yasuhiro; Dif-Pradalier, G.*; Latu, G.*

Plasma Physics and Controlled Fusion, 61(6), p.065015_1 - 065015_15, 2019/05

https://doi.org/10.1088/1361-6587/ab0972

The role of poloidal convective cells on transport processes is studied with the full-F gyrokinetic code GYSELA. For this purpose, we apply a numerical filter to convective cells and compare the simulation results with and without the filter. The energy flux driven by the magnetic drifts turns out to be reduced by a factor of about 2 once the numerical filter is applied. A careful analysis reveals that the frequency spectrum of the convective cells is well-correlated with that of the turbulent Reynolds stress tensor, giving credit to their turbulence-driven origin. The impact of convective cells can be interpreted as a synergy between turbulence and neoclassical dynamics.

Neoclassical transport benchmark of global full-f gyrokinetic simulation in stellarator configurations

Matsuoka, Seikichi; Idomura, Yasuhiro; Satake, Shinsuke*

Physics of Plasmas, 25(2), p.022510_1 - 022510_10, 2018/02

https://doi.org/10.1063/1.5010071

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.

Global kinetic simulations of neoclassical toroidal viscosity in low-collisional perturbed tokamak plasmas

Matsuoka, Seikichi; Idomura, Yasuhiro; Satake, Shinsuke*

Physics of Plasmas, 24(10), p.102522_1 - 102522_9, 2017/10

https://doi.org/10.1063/1.5008285

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.

Impact of plasma parameter on self-organization of electron temperature gradient driven turbulence

Kawai, Chika*; Idomura, Yasuhiro; Maeyama, Shinya*; Ogawa, Yuichi*

Physics of Plasmas, 24(4), p.042303_1 - 042303_13, 2017/04

AA2017-0111.pdf:7.14MB

https://doi.org/10.1063/1.4980005

Self-organization in the slab electron temperature gradient driven (ETG) turbulence is investigated based on gyrokinetic simulations and the Hasegawa-Mima (HM) equation. The scale and the anisotropy of self-organized turbulent structures vary depending on the Rhines scale and the characteristic scale given by the adiabatic response term in the HM equation. The former is determined by competition between the linear wave dispersion and the nonlinear turbulent cascade, while the latter is given as the scale, at which the turbulent cascade is impeded. These scales are controlled by plasma parameters such as the density and temperature gradient, and the temperature ratio of ion to electron. It is found that depending on the plasma parameters, the ETG turbulence shows either isotropic turbulence or zonal flows, which give significantly different transport levels. Although the modulational instability excites zonal modes regardless of the plasma parameters, the final turbulent structure is determined by the self-organization process.

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

https://doi.org/10.1002/ctpp.201610044

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.

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

https://doi.org/10.1063/1.4945618

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.

The Precise energy spectra measurement of laser-accelerated MeV/n-class high-Z ions and protons using CR-39 detectors

Kanasaki, Masato; Jinno, Satoshi*; Sakaki, Hironao; Kondo, Kiminori; Oda, Keiji*; Yamauchi, Tomoya*; Fukuda, Yuji

Plasma Physics and Controlled Fusion, 58(3), p.034013_1 - 034013_6, 2016/03

https://doi.org/10.1088/0741-3335/58/3/034013

In order to understand the synergetic interplay between the Coulomb explosion of clusters and the background gas dynamics, we have conducted ion acceleration experiments using CO clusters (250 nm in dia.) embedded in background H gas with the J-KAREN laser (1 J, 40 fs, 10 contrast) at JAEA-KPSI. By a careful analysis of etch pit positions on CR-39 and their structures including the etch pit growth behavior analysis with the multi-step etching technique, energy spectra for protons from the background gas and carbon/oxygen ions from the clusters are obtained separately. The maximum energies of protons and carbon/oxygen ions are determined as 1.6 MeV and 1.1 MeV/u, respectively. Based on the experimental results, the acceleration mechanism of the background gas ions induced by Coulomb explosion of clusters is discussed with the help from numerical simulations which employ a particle-in-cell (PIC) method including relaxation and ionization processes of plasma particles.