T3FF is a gyrofluid code for computation of isothermal three-dimensional electromagnetic edge turbulence in magnetized plasmas with consistent finite Larmor radius (FLR) treatment. The model allows for arbitrary fluctuation amplitudes (“full-f”) and includes second-order accurate FLR effects in the polarization (“full-k”). The presented code version employs a field-aligned flux-tube geometry for simplified circular toroidal geometry on the closed flux surface edge region of a tokamak plasma. The T3FF code is intended for basic physics studies with the most elementary implementation of a full-f three-dimensional electromagnetic drift wave turbulence model with consistent FLR effects, and as basis for later extension up to a thermal six-moment gyrofluid model. Program Title: T3FF CPC Library link to program files: (to be added by Technical Editor) Developer’s repository link: https://git.uibk.ac.at/c7441036/t3ff Code Ocean capsule: (to be added by Technical Editor) Licensing provisions(please choose one): MIT Programming language: C++ Nature of problem: Solves the isothermal electromagnetic full-f gyrofluid model equations for tokamak edge plasma turbulence, with general FLR effects in the polarization, for simple circular toroidal geometry. Solution method: Finite difference solver for the isothermal gyrofluid equations (Adams-Bashforth scheme, Arakawa scheme) with iterative/FFT solvers for evaluation of the gyrofluid polarization and Ampere’s equations and gyro-averaging operators. Additional comments including restrictions and unusual features: Requires OpenMP, FFTW3

Gyrokinetic simulation of electrostatic turbulence in HL-2A ITB plasma

Thermal helium beam measurements of plasma edge turbulence in positive and negative triangularity plasmas on TCV

Information theory approach to plasma turbulence

Abstract Plasma turbulence refers to the chaotic and random fluctuations observed in almost all laboratory and space plasmas, which imparts complex interactions that leads to energy transfer and cascading across different scales. This article presents results of 2D decaying Hall MHD turbulence occurring in space plasmas with varying ion inertial lengths (and plasma density), using a hybrid PIC code called Menura [1]. It models the particle and field interactions that occur in a bulk plasma with unity plasma beta at the kinetic scales, by solving Maxwell’s and fluid equations. The comparison of the temporal variation of magnetic and kinetic energies and their respective dissipation rates to show the evolution of turbulence. The energy spectra of the in-plane components are plotted across wavenumbers to elucidate their spectral scalings. The inertial range scalings for magnetic and kinetic energy spectra are observed as -5/3 and -3/2, respectively, while the sub-inertial range scalings follows -10/3 and -14/3, respectively. Additionally, the presence of small-scale structures is emphasised through the spatial variations in current density and vorticity contours and with the presence of intermittency in the probability distribution functions of the magnetic field and ion velocity increment. This highlights the prominence of hall effect in shaping the turbulent interaction at small-scales with increasing d i 
.

The interstellar scintillation observed in radio pulsars arises from interference between electromagnetic waves scattered by electron density fluctuations in the turbulent interstellar plasma, providing a critical tool for probing the small-scale structure of the ionized interstellar medium and the pulsar system itself. The primary aim of this work is to study long-term scintillation variations for a bright and nearby pulsar, PSR J0814$+$7429, carried out from September 2013 to September 2023 with the LOw-Frequency ARray (LOFAR) High Band Antennae in the frequency range 120 - 170 MHz. We derived the basic scintillation parameters, scintillation bandwidth (Δν_̊m d), and scintillation timescale (Δτ_̊m d) from the two-dimensional (2D) auto-covariance function of the dynamic spectra that are a 2D matrix of pulse intensity as a function of time and frequency. We present a long-term monitoring study of Δν_̊m d and Δτ_̊m d for PSR J0814$+7429$, which shows a strong annual variation in the time series of the Δτ_̊m d. From our modeling of the annual variations of scintillation velocities, the scattering screen is anisotropic and located at 0.23 kpc from the Earth, likely corresponding to the boundary of the Local Bubble.

Abstract Compressible fluctuations represent a key element of turbulence in astrophysical plasmas, where the compression and expansion of turbulent flows play a critical role in regulating energy transfer and dissipation. In this work, we examine how local streamline topology and energy cascade rate self-organize in plasma turbulence at a fixed scale. Using a fully compressible Hall-magnetohydrodynamic simulation, we quantify the subgrid-scale energy transfer and analyze its relationship to streamline structures by means of gradient-tensor geometric invariants of the velocity field. Our results highlight how streamline topology is crucial for diagnosing turbulence, since the direction of the energy transfer rate is found to be shaped by the local streamline topology. Compressible fluctuations, on the contrary, do not show a clear topological selection in the energy transfer since the overall direction of the local cascade rate is found to be determined by the sign of −∇ · u (plasma volumetric compression or expansion).

Abstract We investigate the magnetic ( B ) and electric ( E ) field spectra in the dissipation range of strong turbulence of a collisionless plasma. This investigation, which is relevant to turbulence studies in many astrophysical settings, is enabled by high-resolution measurements from the four-spacecraft Magnetospheric Multiscale (MMS) mission in the Earth’s magnetotail. B and E spectra are derived as a function of the product of the wave number and electron skin depth ( k d e ) using a novel technique that employs time-delay analysis on multiple intervals of B and E . Using the MMS tetrahedral formation with close (several d e ) spacing, velocities of B and E signals can be derived so that native frequency-based spectra can be accurately translated to k spectra. The most important finding is a mathematically significant break in the B spectral index that appears at k d e ≈ 1 . In the subion range, which spans from the ion inertial length ( d ι ) to d e , the B spectral index is −2.35, then steepens to − 3.13 at sub- d e scales. As expected from previously derived frequency spectra, E has a particularly shallow spectral index (−0.67) in the subion range. At scales smaller than d e and/or the electron thermal gyroradius ( ρ e ), the E spectral index steepens to −2.73. Spectral breaks in both B and E in the dissipation range indicate a change in the physical dissipation processes from ion to electron domination at k d e ≈ 1 . We also confirm that at k ρ e > ~ 2 , the energy density of B and E approaches equipartition, suggesting that energy transfer is near complete.

Tomography serves as an advanced diagnostic tool for analyzing plasma fluctuations and turbulence. However, it requires time-consuming calculations, which impede rapid analysis. Integrating a neural network into tomography offers a potential solution. In this work, we present a trial conducted on a tomography system installed on the Plasma Assembly for Nonlinear Turbulence Analysis, a cylindrical plasma device designed for plasma turbulence research. This article reports on the optimization process of a neural network algorithm and on its excellent properties for tomographic reconstruction, including the extraction of plasma fluctuation properties. The neural network-aided tomography is 25 times faster than and provides comparable accuracy to, the standard algorithm, Maximum Likelihood Expectation Maximization.

A common occurrence in nearly collisionless plasmas is the unequal electron–ion temperatures. The pressure–strain interaction provides a mechanism-agnostic pathway for increasing plasma internal energy through spatiotemporally local isotropic compression and volume-preserving deformation, yet its behavior under thermal disequilibrium remains unexplored. We investigate this using five fully kinetic 2.5-dimensional particle-in-cell simulations of undriven decaying turbulence by varying the initial electron-to-ion temperature ratios. By analyzing the species' internal energy density alongside a decomposition of the pressure–strain interaction, with a focus on the volume-preserving deformation that contains normal and shear contributions, we quantify how the initial temperature imbalance modifies the channels through which turbulence increases each species' internal energy density. The cumulative pressure–strain interaction tracks the change in average internal energy density for both electrons and ions, where the total deformation channel dominates energy evolution. We discover that changes to electron internal energy density are governed primarily by the shear deformation power density, concentrated in electron-scale current sheets, while the ion shear and normal deformation components cancel, yielding a much smaller net deformation power density that peaks around, rather than within, those electron-scale current structures. By varying the initial temperature ratio, we find that the amplitudes and localization of deformation change, but preserve these qualitative trends. Together, these results show how thermal disequilibrium could shape species-dependent turbulent “heating rate,” measured via pressure–strain interaction and now approximated via only its shear deformation part, and provide a framework for interpreting energy evolution and conversion in turbulent space plasmas where unequal species temperature is the norm.

Abstract The plasma energy and particle flows in double-null configurations during MAST L-mode discharges are investigated using the 3D plasma turbulence code STORM. The modelling reproduces key phenomena, such as in-out and up-down heat load asymmetries. Turbulent energy transport, driven by ballooning-like instabilities, dominates the radial energy flux across the last closed flux surface, with over 90% entering the scrape-off layer on the low-field side (LFS). In disconnected geometry (the separation between the two X-points in double-null configurations δr sep ≠0), part of that LFS radial flux is transported to the high field side targets via the secondary X-points, causing the in-out power asymmetry to peak in connected geometries (δ r sep = 0). Differences between lower double null (LDN) and upper double-null (UDN) configurations arise due to the upward electron ∇B drift and clock-wise poloidal E × B drift, leading to higher collisionality and stronger turbulence near the separatrix in LDN but a shorter heat flux decay length. Poloidal energy fluxes to different divertors exhibit in-out asymmetries, with more energy flowing to the primary outer divertor in LDN and UDN. Additionally, the clockwise E × B drift in the primary private flux regions (PFRs) redistributes energy between primary inner-outer divertors, reducing the heat load on LDN’s primary outer target while increasing it in UDN. Thus, for the same |δ r sep |, the total heat loads on primary outer targets in LDN and UDN become comparable. These findings provide insights into plasma and energy transport in double-null configurations, with implications for optimizing divertor performance in fusion reactors.

Abstract Event Horizon Telescope (EHT) images of the supermassive black hole M87* depict an asymmetric ring of emission. General relativistic magnetohydrodynamic (GRMHD) models of M87* and its accretion disk predict that the amplitude and location of the ring’s peak brightness asymmetry should fluctuate due to turbulence in the source plasma. We compare the observed distribution of brightness asymmetry amplitudes to the simulated distribution in GRMHD models, across varying black hole spin a * . We show that, for strongly magnetized (MAD) models, three epochs of EHT data marginally disfavor ∣ a * ∣ ≲ 0.2. This is consistent with the Blandford–Znajek model for M87’s jet, which predicts that M87* should have nonzero spin. We show quantitatively how future observations could improve spin constraints and discuss how improved spin constraints could distinguish between differing jet-launching mechanisms and black hole growth scenarios.

Abstract Plasma waves, turbulence, and shocks are commonly observed in the solar wind. In this study, we investigate the interaction between ion-scale waves and shocks using in situ spacecraft observations. We focus on two possible scenarios: the transmission of waves across shocks, and the local generation of waves through kinetic instabilities. We examine two shock events observed by Solar Orbiter: one at Earth’s bow shock, and the other an interplanetary shock located at approximately 0.5 au. Both events exhibit ion-scale wave activity upstream and downstream of the shocks. Based on the relationship between the upstream and downstream wave frequencies and wavevector magnitudes, we find no clear evidence supporting a simple transmission of ion-scale waves across the shock in these events. By analyzing the observed ion velocity distribution functions, we find that the ion-scale waves near shocks are more likely generated locally by ion-driven kinetic instabilities, in contrast to the behavior of MHD-scale turbulence. These results indicate that local plasma conditions play a dominant role in shaping kinetic-scale waves in the vicinity of shocks.

The relaxation of many physical systems is constrained by collisions. However, most space and astrophysical plasmas are nearly collisionless, leaving open questions about the pathways of energy transfer and dissipation. In many turbulent plasmas, the electric field takes on the role of energy transfer leading to dissipation. Using measurements from the Magnetospheric Multiscale Mission, we study the statistical properties of the electric field spectrum in the kinetic range of strong turbulence generated by magnetic reconnection in the Earth's magnetotail. From the inertial to the kinetic range (often called the dissipation range) of scales, we find that turbulent fluctuations develop increasingly non-Gaussian features. The kinetic range contains two regimes with distinct behaviors in the power spectrum and measures of non-Gaussianity. In the subelectron kinetic regime (smaller than the electron gyroradius), the turbulence becomes isotropic and exhibits energy equipartition between the electric field and magnetic field. Our analyses indicate (1)a growing presence of intermittent structures that are expected to lead to enhanced energy dissipation, (2)changes in the electric field dynamics at the transitions between turbulence regimes, and (3)an asymptotic relaxation to a state of energy equipartition in the electromagnetic field in the subelectron kinetic range, where the energy transfer between the magnetic and electric fields appears to be near complete. These results reveal the importance of the electric field in mediating turbulence dissipation and relaxation in collisionless plasmas.

Abstract An international team from several laboratories and universities has made key advances over the last few years in the control of plasma transport and edge instabilities with applied 3D fields in the KSTAR tokamak to optimize long pulse operation scenarios. This overview begins with the optimization of both core and edge resonant magnetic perturbations (RMPs) to improve fast ion confinement to avoid excessive limiter heat loads due to fast ion losses and successful modeling of the experimental results. Integrated and advanced plasma control techniques with machine learning (ML) and adaptive control were then used to optimize the 3D field spectrum in real-time to control edge localized modes (ELMs) while avoiding core locked modes that could disrupt the plasma. Accelerating the offline model of 3D fields with a surrogate ML model can optimize ELM suppression in the edge while limiting the impact of the applied RMP fields deeper in the plasma core in real-time. In addition, the impact of the 3D fields on the divertor heat load has been modeled and compared with experimental measurements. An analysis of a multi-machine database including KSTAR has been performed to better understand the metrics for the observed RMP thresholds for ELM suppression and the resulting plasma performance. Predictive modeling of the operational space for ELM suppression and density pumpout due to RMP has shown the importance of magnetic islands in the plasma edge and their impact on plasma turbulence. This research has culminated in the development of successful long pulse operational scenarios on KSTAR while attempting to overcome challenges of the new tungsten divertor.

Abstract Coherent structures created through turbulent cascades play a key role in energy dissipation and particle acceleration. In this work, we investigate both current and vorticity sheets in 3D particle-in-cell simulations of decaying relativistic turbulence in pair plasma by training a self-organizing map to recognize these structures. We subsequently carry out an extensive statistical analysis to reveal their geometric and structural properties. This analysis is systematically applied across a range of magnetizations ( σ ) and fluctuating-to-mean magnetic field strengths ( δB 0 / B 0 ) to assess how these parameters influence the resulting structures. We find that the structures’ geometric properties form power-law distributions in their probability density functions, with the exception of the structure width, which generally exhibits an exponential distribution peaking around two electron skin depths. The measurements show a weak dependence on σ but a strong dependence on δB 0 / B 0 . Finally, we investigate the spatial relationship between current sheets and vorticity sheets. We find that most current sheets are directly associated with at least one vorticity sheet neighbor and are often situated between two vorticity sheets. These findings provide a detailed statistical framework for understanding the formation and organization of coherent structures in relativistic magnetized turbulence, allowing for their incorporation into updated theoretical models for structure-based energy dissipation and particle acceleration processes crucial for interpreting high-energy astrophysical observations.

The role of zonal flow (ZF) in the turbulence saturation of trapped electron modes (TEM) in magnetically confined plasmas is revisited. In this study, we examine ZF excitation and saturation mechanisms in TEM turbulence using detailed free-energy transfer diagnostics from nonlinear gyrokinetic simulations. When the ion channel becomes subdominant, electrons shift to transferring energy to the zonal component, which results in zonal flows always playing a significant though subdominant role, in the case of the temperature gradient driven TEM. The velocity-space structure of energy transfer reveals that trapped electrons directly couple to ZF. Regarding the saturation physics, the zonal flow advection, drift-wave-drift-wave interactions, and stable modes at the pump waves are compared. When ZF saturation is weak, drift-wave-drift-wave interactions play a larger role in maintaining turbulence saturation. The findings elucidate the roles of nonzonal to zonal flow coupling, stable modes, and nonzonal wave-wave interactions, and provide a basis for improving reduced models of turbulent transport.

Abstract The interaction between a turbulent plasma flow, such as the solar or stellar wind, and a magnetic field acting as an obstacle is a common phenomenon in space and astrophysical plasmas. The Earth's magnetosphere is formed precisely as a result of this interaction, and there is extensive evidence suggesting that the geomagnetic tail behaves like a turbulent wake behind an obstacle. Unlike an ordinary wake, the geomagnetic tail is divided into a plasma sheet, filled with dense, turbulent plasma, and tail lobes filled with rarefied, quasi-laminar plasma. The interaction between the turbulent plasma sheet and the inner magnetosphere is crucial for understanding key magnetospheric processes such as geomagnetic storms and substorms. Meanwhile, variations in solar wind density, velocity, and the interplanetary magnetic field (IMF) simultaneously affect plasma conditions in both the plasma sheet and the inner magnetosphere, although through different and not yet fully understood mechanisms. In this work, data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission are used to analyze the influence of the IMF and solar wind dynamic pressure on eddy diffusion within the plasma sheet. 
Our results indicate that eddy diffusion coefficients increase with a southward orientation of the IMF and can intensify by more than an order of magnitude under high values of the solar wind dynamic pressure. Both of these factors contribute to an increase in the plasma beta parameter within the plasma sheet, leading to a shift of the transition zone between turbulent and quasi-laminar plasmas towards Earth.

Magnetically confined fusion plasmas exhibit predator-prey-like cyclic oscillations through the self-regulating interaction between drift-wave turbulence and zonal flow. To elucidate the detailed mechanism and causality underlying this phenomenon, we construct a simple stochastic predator-prey model that incorporates intrinsic fluctuations and analyze its statistical properties from an information-theoretic perspective. We first show that the model exhibits persistent fluctuating cyclic oscillations called quasicycles due to amplification of intrinsic noise. This result suggests the possibility that the previously observed periodic oscillations in a toroidal plasma are not limit cycles, but quasicycles, and that such quasicycles may be widely observed under various conditions. For this model, we further prove that information of the zonal flow is propagated to turbulence. This result suggests that turbulence behavior may be predictable to a certain extent based on zonal flow characteristics.

Abstract It has been hypothesized that Meteor Radio Afterglows (MRAs) occur due to resonant transition radiation (RTR) where suprathermal electrons emit as they pass through electron density inhomogeneities in a turbulent plasma. Meteor trails are thought to produce suprathermal electrons through anion oxidation, which can be identified through meteor persistent trains. Meteor plasma turbulence can be identified through a non‐specular echo from a meteor radar. We present the first radar observations of a MRA that was also observed to produce a non‐specular echo and a persistent train, which indicate the presence of both plasma turbulence and anion oxidation. The observations were made using the Long Wavelength Array station at Sevilleta (LWA‐SV) and the Spread spectrum Interferometric Multi‐static Meteor radar Observing Network in New Mexico (SIMONe‐NM), the Widefield Persistent Train Camera version 2 (WiPT2) and the Global Meteor Network (GMN). Analysis reveals that while the MRA was spatially coincident a range‐spread, non‐specular echo, the brightest MRA emission came from a portion of the trail 8 km higher than the brightest radar scatter. We find that changes in the mean free path and collision frequency may be responsible for the higher altitude emission despite weaker plasma turbulence there. We also present evidence from the SIMONe‐NM head echo that the MRA and non‐specular echo were coincident with fragmentation of the meteoroid, which may have some role to play in both phenomena.