Article
Physics, Fluids & Plasmas
Javier H. Nicolau, Gyungjin Choi, Jingyuan Fu, Pengfei Liu, Xishuo Wei, Zhihong Lin
Summary: The helical components of the equilibrium magnetic field have significant impacts on zonal flow, while kinetic electrons can reduce zonal flow residue and increase the frequency of low frequency oscillation. Additionally, linear toroidal coupling of multiple toroidal n-harmonics barely affects zonal flows but can generate long wavelength toroidal harmonics with the same toroidal number as the helical magnetic field.
Article
Physics, Fluids & Plasmas
J. Smoniewski, E. Sanchez, I. Calvo, M. J. Pueschel, J. N. Talmadge
Summary: The linear collisionless damping of zonal flows in quasi-symmetric stellarator equilibria was investigated, revealing the impact of zonal flow oscillations and long-time damping on zonal flow evolution, with the zonal flow residual tending to zero for small radial wave-number. The oscillation frequency and damping rate depend on the bounce-averaged radial particle drift, with calculations accurately reproducing the full-volume long-time residual for moderate k(x).
PHYSICS OF PLASMAS
(2021)
Article
Physics, Fluids & Plasmas
O. D. Guercan, J. Anderson, S. Moradi, A. Biancalani, P. Morel
Summary: This article revisits the phase and amplitude dynamics of the Hasegawa-Wakatani system and finds that a single resonant triad can saturate via phase locking, while non-resonant triads show similar behavior only when one of its legs is a zonal wave number. Additionally, the behavior of the resulting triad pair becomes more complex when an additional triad is included as a reflection.
PHYSICS OF PLASMAS
(2022)
Article
Physics, Fluids & Plasmas
T. Ullmann, B. Schmid, P. Manz, G. E. M. Tovar, M. Ramisch
Summary: This study investigates the influence of background shearing rate on energy transfer between turbulence and zonal flows in different shear regimes, using the k - epsilon model. Linear dependency of Reynolds stress and quadratic dependency of energy transfer on shearing rate are found, along with a redistribution of spectral power towards zonal flow. The increase in relative zonal power is even higher beyond the transition to the strong shear regime.
PHYSICS OF PLASMAS
(2021)
Article
Physics, Fluids & Plasmas
Roscoe White
Summary: Particle resonances in stellarators can generate islands in the region of passing particle orbits. The resonance period must match the period of the equilibrium magnetic field. Resonances form islands on surfaces where the orbital helicity matches the field period. Trapped particles bouncing on these surfaces with matching helicity will experience periodic loss due to drift.
PHYSICS OF PLASMAS
(2022)
Article
Mechanics
Stephane Perrard, Alienor Riviere, Wouter Mostert, Luc Deike
Summary: In this study, the deformation modes and lifetime of a bubble in a turbulent flow are investigated through numerical simulations and theoretical analysis. Two temporal regimes are observed during the bubble deformation process, with the first regime driven by inertial forces and the second regime resulting from a balance between inertial forces and surface tension.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Multidisciplinary Sciences
Ermanno Brosch, Gert Lube, Matteo Cerminara, Tomaso Esposti-Ongaro, Eric C. P. Breard, Josef Dufek, Betty Sovilla, Luke Fullard
Summary: Pyroclastic surges are destructive hazards from volcanoes, with dynamic pressure energy mainly carried by large-scale coherent turbulent structures and gravity waves. Real-world flows exhibit destructiveness through the development of approximately 1-20 successive high-pressure pulses per minute.
NATURE COMMUNICATIONS
(2021)
Article
Mechanics
Alienor Riviere, Wouter Mostert, Stephane Perrard, Luc Deike
Summary: This study investigates the dynamics and statistics of bubble break-up in homogeneous and isotropic turbulence through direct numerical simulations, focusing on the influence of the Weber number on bubble break-up dynamics. The findings reveal that during the transition to stable conditions, bubble break-up occurs through both local and non-local production processes, resulting in a range of bubble sizes.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Astronomy & Astrophysics
T. Gastine, J. Wicht
Summary: The ongoing NASA's Juno mission has placed new constraints on the internal dynamics of Jupiter, revealing a complex internal structure with a dipole-dominated surface magnetic field and a stratification of metallic and molecular hydrogen. The simulations show that in Jupiter's metallic core, magnetic energy is nearly an order of magnitude larger than kinetic energy, while kinetic energy is mainly pumped into zonal flows in the molecular envelope.
Article
Physics, Fluids & Plasmas
P-Y Li, P. W. Terry
Summary: The saturation physics of ion temperature gradient turbulence is explored using a hierarchy of reduced models. The study shows that accurate amplitude prediction requires coupling between unstable mode, stable mode, and zonal flow in the models.
PHYSICS OF PLASMAS
(2022)
Article
Engineering, Electrical & Electronic
Lukas Koelsch, Lena Zellmann, Rishabh Vyas, Martin Pfeifer, Soeren Hohmann
Summary: Zonal pricing is a suitable mechanism for incentivizing grid-supporting behavior in large-scale power systems. Through the creation of individual price zones and appropriate price signals based on local grid conditions, frequency, voltage stability, and Pareto efficiency can be ensured. Using a dynamic network model and distributed continuous-time control laws that require only neighbor-to-neighbor communication, the effectiveness of zonal pricing compared to isolated grid operation is demonstrated.
IEEE TRANSACTIONS ON POWER SYSTEMS
(2022)
Article
Physics, Multidisciplinary
Cody J. Reeves, Igor S. Aranson, Petia M. Vlahovska
Summary: The researchers developed a continuum model for mixtures of clockwise and counterclockwise Quincke spinners in a fluid system, showing the emergence of same-spin phase separation, traffic lanes, sustained turbulent-like motion, and a chirality breaking transition depending on the fluid inertia.
COMMUNICATIONS PHYSICS
(2021)
Article
Mechanics
Xuan Zhang, Robert E. Ecke, Olga Shishkina
Summary: In rapidly rotating turbulent Rayleigh-Benard convection with a small Prandtl number fluid in slender cylindrical containers, a boundary zonal flow (BZF) is found to develop near the sidewall, carrying a disproportionate amount of heat transport for Pr < 1 but decreasing abruptly for larger Pr. The BZF is robust and appears in containers of different aspect ratios and over a broad range of Pr and Ra values.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Kazuki Maeda, Masanobu Date, Kazuyasu Sugiyama, Shu Takagi, Yoichiro Matsumoto
Summary: A series of experiments and modelling were conducted to study the interaction of a pair of spherical bubbles rising in a vertical channel. The results showed that bubbles take two preferential configurations depending on their mutual distance, which helps to elucidate the clustering mechanisms.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
E. Elmakies, O. Shildkrot, N. Kleeorin, A. Levy, I Rogachevskii, A. Eidelman
Summary: This experimental study investigates the turbulent thermal diffusion of small particles in inhomogeneous and anisotropic stably stratified turbulence. The results show that particles accumulate at the minimum of mean fluid temperature.
Article
Physics, Fluids & Plasmas
S. Toda, M. Nunami, H. Sugama
JOURNAL OF PLASMA PHYSICS
(2020)
Article
Physics, Fluids & Plasmas
M. Nunami, M. Nakata, S. Toda, H. Sugama
PHYSICS OF PLASMAS
(2020)
Article
Physics, Fluids & Plasmas
H. Sugama, S. Matsuoka, M. Nunami, S. Satake
Summary: This study presents the Eulerian variational formulation of the gyrokinetic system with electrostatic turbulence in general spatial coordinates. The invariance of the Lagrangian is used to derive the local momentum balance equation, and modifications to the momentum balance with collision and external source terms are investigated. The results obtained are considered useful for global gyrokinetic simulations in non-axisymmetric toroidal systems studying neoclassical and turbulent transport processes.
PHYSICS OF PLASMAS
(2021)
Article
Physics, Fluids & Plasmas
S. Matsuoka, H. Sugama, Y. Idomura
Summary: The study implemented an improved collision operator in a global full-f gyrokinetic simulation and successfully reproduced the neoclassical thermal diffusivity, showing higher accuracy in the higher collisionality regime compared to the original operator. The improved operator effectively addressed the overestimation issues observed in the original operator, demonstrating correct retention of collisional processes described by the exact operator.
PHYSICS OF PLASMAS
(2021)
Article
Physics, Multidisciplinary
Felix Warmer, K. Tanaka, P. Xanthopoulos, M. Nunami, M. Nakata, C. D. Beidler, S. A. Bozhenkov, M. N. A. Beurskens, K. J. Brunner, O. P. Ford, G. Fuchert, H. Funaba, J. Geiger, D. Gradic, K. Ida, H. Igami, S. Kubo, A. Langenberg, H. P. Laqua, S. Lazerson, T. Morisaki, M. Osakabe, N. Pablant, E. Pasch, B. Peterson, S. Satake, R. Seki, T. Shimozuma, H. M. Smith, T. Stange, A. Stechow, H. Sugama, Y. Suzuki, H. Takahashi, T. Tokuzawa, T. Tsujimura, Y. Turkin, R. C. Wolf, I Yamada, R. Yanai, R. Yasuhara, M. Yokoyama, Y. Yoshimura, M. Yoshinuma, D. Zhang
Summary: The magnetic field configuration in modern fusion devices is assessed by comparing experiments with the same heating power between a stellarator and a heliotron. Turbulence plays a key role in the optimized stellarator, while neoclassical processes largely determine the transport in the heliotron device. Gyrokinetic simulations elucidate the underlying mechanisms promoting stronger ion scale turbulence in the stellarator. Similar plasma performances in these experiments suggest that neoclassical and turbulent transport should both be optimized in next step reactor designs.
PHYSICAL REVIEW LETTERS
(2021)
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
H. Sugama, S. Matsuoka, M. Nunami
Summary: Expressions of polarization and magnetization in magnetically confined plasmas are derived, which include full expansions in the gyroradius to treat effects of both equilibrium and microscopic electromagnetic turbulence. Using the obtained expressions, densities and flows of particles are related to those of gyrocenters. To the first order in the normalized gyroradius expansion, the mean part of the particle flow is given by the sum of the gyrocenter flow and the magnetization flow, which corresponds to the so-called magnetization law in drift kinetics, while the turbulent part contains the polarization flow as well.
PHYSICS OF PLASMAS
(2022)
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
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
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, 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)
