Article
Physics, Fluids & Plasmas
Mikiya Muto, Kenji Imadera, Yasuaki Kishimoto
Summary: In this study, entropy balances and radial dynamics were investigated in toroidal flux-driven ion-temperature-gradient turbulence using newly derived coupled equations and full-f gyrokinetic simulations. It was found that the fluctuations in entropy production due to collisional dissipation and thermodynamic entropy reduction due to energy input/output were balanced through the generation of heat flux and associated phase mixing in the radial direction. The cross-correlation analysis revealed that collisional dissipation occurs after the formation of fine-scale structures by phase mixing, while thermodynamic entropy production is in-phase with heat flux, except in regions exhibiting heat avalanches where the relationship is violated due to advection-dominated thermodynamic entropy.
PHYSICS OF PLASMAS
(2021)
Article
Physics, Fluids & Plasmas
Amit K. K. Singh, J. Mahapatra, J. Chowdhury, D. Aggarwal, T. Hayward-Schneider, R. Ganesh, E. Lanti, L. Villard
Summary: In this work, linear and nonlinear collisionless electrostatic simulations were conducted to study the standard and short wavelength ion temperature gradient mode (SWITG) in the ADITYA-U tokamak. The simulations showed the coexistence of the SWITG mode and the standard ion temperature gradient (ITG) mode in ADITYA-U due to steep density and temperature gradients. Good agreement was observed in the growth rate and real frequency values between the linear global eigenvalue gyrokinetic code GLOGYSTO and the nonlinear global gyrokinetic particle-in-cell code ORB5. Linear stability analysis revealed the suppression of SWITGs for low values of R-0/L-T, leaving only the standard ITG mode unstable. Nonlinear simulations confirmed the minimal contribution of SWITG mode to thermal ion heat transport due to the zonal flow shearing effect.
Article
Computer Science, Interdisciplinary Applications
PengFei Zhao, Lei Ye, Nong Xiang
Summary: A new method based on time diffusion technique is developed to mitigate numerical instability caused by high frequency electrostatic shear Alfven wave in gyrokinetic simulation of electrostatic turbulence. It fully preserves drift-kinetic electron effects and can be efficiently incorporated with explicit time integration scheme, successfully applied to linear and nonlinear ITG/TEM turbulence simulations, improving numerical stability and enlarging time step size in electrostatic turbulence simulation in tokamaks.
COMPUTER PHYSICS COMMUNICATIONS
(2021)
Article
Physics, Fluids & Plasmas
D. I. Palade
Summary: In this study, the effects of ion temperature gradient (ITG) and trapped electron mode (TEM) turbulence on the transport coefficients of low-Z impurities in fusion plasmas are analyzed using a statistical test-particle approach. It is found that the convection of E x B motion by the polarization drift drives an outward radial pinch via ITG and an inward pinch via TEM turbulence. Opposite radial pinches are driven by turbulent motion along magnetic field-lines. The theoretical framework is validated through comparison with experimental data on the transport of Boron impurities.
Article
Physics, Fluids & Plasmas
Lianjie Ma, Debing Zhang, Limin Yu, Erbing Xue, Xianmei Zhang, Juan Huang, Yong Xiao, Xianzu Gong, Jinping Qian, EAST Team
Summary: The parameter dependence of transition between electrostatic instabilities is examined using gyrokinetic simulation based on a steady-state discharge in the Experimental Advanced Superconducting Tokamak. It is found that the trapped electron mode dominates around the core while the ion temperature gradient mode dominates outside. The study also reveals that TEM is dominant when the electron-ion temperature ratio is higher than 0.5 and decreases as the density gradient decreases.
PLASMA SCIENCE & TECHNOLOGY
(2023)
Article
Physics, Fluids & Plasmas
Kenji Imadera, Yasuaki Kishimoto
Summary: The formation mechanism of internal transport barriers in flux-driven turbulence is studied using the full-f gyrokinetic code GKNET. In the adiabatic electron case with a weak magnetic shear configuration, toroidal momentum injection changes the radial mean electric field through radial force balance, leading to driven ITB formation. In the kinetic electron case with a reversed magnetic shear configuration, robust co-intrinsic rotation is driven near the qmin surface in ITG turbulence and sustains the E-r shear through radial force balance, leading to spontaneous reduction of ion turbulent thermal diffusivity.
PLASMA PHYSICS AND CONTROLLED FUSION
(2023)
Article
Physics, Fluids & Plasmas
Jingchun Li, J. Q. Xu, Y. R. Qu, Z. Lin, J. Q. Dong, X. D. Peng, J. Q. Li
Summary: The effect of island width on the interactions between magnetic island and ion temperature gradient turbulence is investigated using the global gyrokinetic approach. It is observed that the coupling between the island and turbulence is strengthened with larger island width. Vortex flow, sensitive to the island width, triggers a potent E x B shear flow and reduces turbulent transport. The shearing rate is minimum at the O-point and maximum at the X-points of the island, regardless of the island width. The relationship between zonal flow amplitude and island width is nonmonotonic, with medium-sized islands partially suppressing it and large islands enhancing it. Larger islands damage the ITG mode structure, increasing turbulent transport at the X-point and decreasing it at the O-point. However, at very small island widths, the turbulence near the X-point is hardly affected while still suppressed inside the island. The influence of different island sizes on turbulence transport is also discussed.
Article
Physics, Fluids & Plasmas
J. Citrin, S. Maeyama, C. Angioni, N. Bonanomi, C. Bourdelle, F. J. Casson, E. Fable, T. Goerler, P. Mantica, A. Mariani, M. Sertoli, G. Staebler, T. Watanabe
Summary: Previous studies suggested that ETG turbulence could lead to an anti-gyroBohm isotope scaling in JET high-performance hybrid H-mode scenarios. However, a comparison study with higher-fidelity turbulence modeling invalidates this claim and shows that ion-scale turbulence with magnetic field perturbations can match the power balance fluxes within temperature gradient error margins. Multiscale gyrokinetic simulations from two distinct codes also demonstrate the absence of significant ETG heat flux, indicating that simple rules-of-thumb are insufficient criteria for its onset.
Article
Physics, Fluids & Plasmas
M. D. J. Cole, A. Mishchenko, A. Bottino, C. S. Chang
Summary: In this paper, global gyrokinetic simulation of the ion temperature gradient-driven mode-kinetic ballooning mode transition in a toroidal fusion plasma test case was successfully demonstrated using the MV/PT scheme with the particle-in-cell codes XGC and ORB5. The MV/PT scheme combines explicit time integration with mitigation of the electromagnetic gyrokinetic cancelation problem, showing good agreement with results from a conventional continuum code.
PHYSICS OF PLASMAS
(2021)
Article
Physics, Fluids & Plasmas
P. -Y. Li, M. J. Pueschel, P. W. Terry, G. G. Whelan
Summary: The onset of turbulent heat transport at a higher temperature gradient than the critical gradient of linear instability, known as the Dimits shift, is a recurring feature of nonlinear simulations for magnetically confined fusion plasmas. Resonance in the nonlinear coupling between the modes that dominate energy transfer can lead to suppression of turbulence and transport above the linear critical gradient. By incorporating corresponding saturation physics, the standard quasilinear model for rapid heat flux prediction is improved, which can now predict reduced heat flux in the Dimits regime.
Article
Physics, Fluids & Plasmas
M. J. Pueschel, P. -Y. Li, P. W. Terry
Summary: The improved quasilinear model accurately predicts transport in fusion devices, especially in zonal-flow-saturated turbulence regimes. The modification tracks changes in saturation efficiency using frequency mismatch between interacting modes, rapidly increasing the efficacy of nonlinearity. This model also yields significantly improved predictions for trapped-electron-mode transport.
Article
Physics, Fluids & Plasmas
Qingjiang Pan, Darin R. Ernst, David R. Hatch
Summary: This study goes beyond previous models by using an accurate gyrokinetic Fokker-Planck collision operator to demonstrate important corrections in simulating turbulence in magnetically confined fusion plasmas, showing significant improvements in predicting particle and energy loss while reducing computational demands.
Article
Physics, Fluids & Plasmas
S. Toda, M. Nunami, H. Sugama
Summary: This paper presents a transport simulation of turbulent heat transport using reduced transport models. The simulation results are consistent with nonlinear gyrokinetic simulation, and the computational cost is lower.
PLASMA PHYSICS AND CONTROLLED FUSION
(2022)
Article
Engineering, Multidisciplinary
Yasasya Batugedara, Alexander E. Labovsky, Kyle J. Schwiebert
Summary: A new family of turbulence models, LES-C, has been proposed, which reduces modeling error by treating an LES model as a defect solution and then correcting it on the same spatial mesh. In numerical tests, all LES-C models outperform their LES counterparts.
COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING
(2024)
Article
Physics, Fluids & Plasmas
D. S. Oliveira, T. Body, D. Galassi, C. Theiler, E. Laribi, P. Tamain, A. Stegmeir, M. Giacomin, W. Zholobenko, P. Ricci, H. Bufferand, J. A. Boedo, G. Ciraolo, C. Colandrea, D. Coster, H. de Oliveira, G. Fourestey, S. Gorno, F. Imbeaux, F. Jenko, V. Naulin, N. Offeddu, H. Reimerdes, E. Serre, C. K. Tsui, N. Varini, N. Vianello, M. Wiesenberger, C. Wuethrich
Summary: In this study, self-consistent full-size turbulent-transport simulations of the divertor and scrape-off-layer of tokamaks are performed. A dataset called TCV-X21 is built for the validation of edge turbulence models, and three flux-driven 3D fluid-turbulence models are validated using this dataset. The results show that the simulations match the experimental profiles for most observables at the outboard midplane, but have comparatively poorer agreement towards the divertor targets.
Article
Physics, Fluids & Plasmas
E. Narita, M. Honda, S. Maeyama, T-H Watanabe
Summary: A neural-network based model has been developed to accurately forecast the saturation time of turbulent heat fluxes in nonlinear gyrokinetic simulations. The model focuses on wavenumber space images to represent turbulence characteristics and utilizes a convolutional neural network to detect differences between images and classify the phase of turbulence evolution. It can also predict the simulation time with high accuracy and enable the search for an ideal initial condition that leads to rapid simulation saturation.
Article
Physics, Fluids & Plasmas
J. Citrin, S. Maeyama, C. Angioni, N. Bonanomi, C. Bourdelle, F. J. Casson, E. Fable, T. Goerler, P. Mantica, A. Mariani, M. Sertoli, G. Staebler, T. Watanabe
Summary: Previous studies suggested that ETG turbulence could lead to an anti-gyroBohm isotope scaling in JET high-performance hybrid H-mode scenarios. However, a comparison study with higher-fidelity turbulence modeling invalidates this claim and shows that ion-scale turbulence with magnetic field perturbations can match the power balance fluxes within temperature gradient error margins. Multiscale gyrokinetic simulations from two distinct codes also demonstrate the absence of significant ETG heat flux, indicating that simple rules-of-thumb are insufficient criteria for its onset.
Article
Multidisciplinary Sciences
Shinya Maeyama, Tomo-Hiko Watanabe, Motoki Nakata, Masanori Nunami, Yuuichi Asahi, Akihiro Ishizawa
Summary: This study explores the cross-link interaction between electron- and ion-scale turbulences in fusion plasma and its implications. The authors find that electron-scale turbulence disturbs ion-scale micro-instability and reduces large-scale turbulent fluctuations, demonstrating the possibility of reduced heat flux through cross-scale interactions.
NATURE COMMUNICATIONS
(2022)
Article
Physics, Fluids & Plasmas
T. Moritaka, H. Sugama, M. D. J. Cole, R. Hager, S. Ku, C. S. Chang, S. Ishiguro
Summary: This study examines the isotope effects under a radial electric field in a helical magnetic field configuration. The results show that in single-ion-species plasmas, the heat flux exhibits a mass number dependency consistent with gyro-Bohm scaling. However, in multi-ion-species plasmas with a global radial electric field or a heavy hydrogen component, the heat flux shows favorable mass number dependencies that violate gyro-Bohm scaling.
Article
Physics, Fluids & Plasmas
M. Nunami, S. Toda, M. Nakata, H. Sugama
Summary: A novel scheme is developed to predict the turbulent transport of ion heat in magnetic confined plasmas by combining mathematical optimization techniques and first-principle gyrokinetic simulations. The scheme can reduce computational costs and realize predictions for turbulent transport.
PHYSICS OF PLASMAS
(2022)
Article
Physics, Fluids & Plasmas
Mitsuru Honda, Emi Narita, Shinya Maeyama, Tomo-Hiko Watanabe
Summary: A multimodal convolutional neural network model was developed to predict electrostatic turbulent heat fluxes based on images and values generated by nonlinear gyrokinetic simulations. The model successfully predicted times and fluxes with high accuracy for both test data and unknown cases.
CONTRIBUTIONS TO PLASMA PHYSICS
(2023)
Article
Physics, Fluids & Plasmas
T. -h. Watanabe, S. Maeyama, M. Nakata
Summary: Multi-scale gyrokinetic theory and simulations have revealed cross-scale interactions between the trapped electron mode (TEM) and the electron temperature gradient (ETG) turbulence in a toroidal magnetized plasma. The TEM instability growth rate is reduced in the presence of ETG turbulence, which is well represented by effective diffusion. A theoretical model based on stochastic forcing by the ETG turbulence accurately describes the observed turbulent diffusion coefficient in multi-scale turbulence simulations.
Article
Physics, Fluids & Plasmas
T. -H. Watanabe, J. Hiwatari, S. Maeyama
Summary: The study extends the analysis of eigenvalue feedback instability in a magnetosphere-ionosphere (M-I) coupling model to understand the stabilization mechanism of high-frequency shear Alfven modes. It is found that the stabilization of high-frequency modes is attributed to the change of effective impedance due to the non-uniform ionospheric conductivity, rather than the collision-induced flow shear. Low-frequency modes relevant to auroral arc excitation remain unstable. An effective impedance model incorporating the inhomogeneous conductivity profile is also developed as an extension of the height-integrated ionosphere model.
PHYSICS OF PLASMAS
(2023)
Article
Physics, Fluids & Plasmas
M. Niiro, A. Ishizawa, Y. Nakamura, S. Maeyama, T-H Watanabe
Summary: This study investigates the plasma beta dependence of ion temperature gradient (ITG) driven turbulence. It is found that the Shafranov shift cancels out the electromagnetic stabilizing effect on the ITG mode, leading to an unchanged growth rate as beta increases. The turbulent energy transport does not decrease with beta as suggested by the s - alpha model. Additionally, the Shafranov shift significantly increases the critical onset beta value for the kinetic ballooning mode.
PLASMA PHYSICS AND CONTROLLED FUSION
(2023)
Article
Physics, Fluids & Plasmas
M. Honda
Summary: This study investigates the roles of momentum conservation and the self-adjointness of the collision operator in the neoclassical particle flux. The results confirm the importance of considering the electron flux when modeling neoclassical impurity fluxes.
PHYSICS OF PLASMAS
(2023)
Article
Physics, Multidisciplinary
Shaokang Xu, S. Maeyama, T. -H. Watanabe
Summary: Turbulence-driven heavy ion transport in hot magnetized plasma is investigated using gyrokinetic theory and simulations. A finite heavy ion parallel compressibility pinch is discovered, contrary to the conventional understanding. Perturbation theory clarifies the frequency dependence of the pinch, resolving the discrepancy with experimental observations. Additionally, a nonlocal approach predicts strong anisotropy of the pinch on a magnetic surface. The research also reveals the effects of heavy ion mass on the pinch and the possibility of pinch direction reversal in nonlinear trapped electron mode turbulence through inverse cascade.
PHYSICAL REVIEW RESEARCH
(2022)
