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1. Intermittency and Dissipative Structures Arising from Relativistic Magnetized Turbulence

   https://doi.org/10.3847/1538-4357/ad284c  

   Davis, Zachary; Comisso, Luca; Giannios, Dimitrios (March 2024, The Astrophysical Journal)

   Abstract Kinetic simulations of relativistic turbulence have significantly advanced our understanding of turbulent particle acceleration. Recent progress has highlighted the need for an updated acceleration theory that can account for particle acceleration within the plasma’s coherent structures. Here, we investigate how intermittency modeling connects statistical fluctuations in turbulence to regions of high-energy dissipation. This connection is established by employing a generalized She–Leveque model to characterize the exponentsζ_pfor the structure functions $S^p\propto l^{{\zeta }_p}$. The fitting of the scaling exponents provides us with a measure of the codimension of the dissipative structures, for which we subsequently determine the filling fraction. We perform our analysis for a range of magnetizationsσand relative fluctuation amplitudesδB₀/B₀. We find that increasing values ofσandδB₀/B₀allow the turbulent cascade to break sheetlike structures into smaller regions of dissipation that resemble chains of flux ropes. However, as their dissipation measure increases, the dissipative regions become less volume filling. With this work, we aim to inform future turbulent acceleration theories that incorporate particle energization from interactions with coherent structures within relativistic turbulence. 

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2. Electron and Proton Energization in 3D Reconnecting Current Sheets in Semirelativistic Plasma with Guide Magnetic Field

   https://doi.org/10.3847/2041-8213/ad2fa5  

   Werner, Gregory R; Uzdensky, Dmitri A (March 2024, The Astrophysical Journal Letters)

   Abstract Using 3D particle-in-cell simulation, we characterize energy conversion, as a function of guide magnetic field, in a thin current sheet in semirelativistic plasma, with relativistic electrons and subrelativistic protons. There, magnetic reconnection, the drift-kink instability (DKI), and the flux-rope kink instability all compete and interact in their nonlinear stages to convert magnetic energy to plasma energy. We compare fully 3D simulations with 2D in two different planes to isolate reconnection and DKI effects. In zero guide field, these processes yield distinct energy conversion signatures: ions gain more energy than electrons in 2Dxy(reconnection), while the opposite is true in 2Dyz(DKI), and the 3D result falls in between. The flux-rope instability, which occurs only in 3D, allows more magnetic energy to be released than in 2D, but the rate of energy conversion in 3D tends to be lower. Increasing the guide magnetic field strongly suppresses DKI, and in all cases slows and reduces the overall amount of energy conversion; it also favors electron energization through a process by which energy is first stored in the motional electric field of flux ropes before energizing particles. Understanding the evolution of the energy partition thus provides insight into the role of various plasma processes, and is important for modeling radiation from astrophysical sources such as accreting black holes and their jets. 

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3. Solar Eruption Onset and Particle Acceleration in Nested-null Topologies

   https://doi.org/10.3847/1538-4357/ae0e65  

   Kumar, Pankaj; Karpen, Judith T; Wyper, Peter F; Lario, David; Antiochos, Spiro K; DeVore, C Richard (November 2025, The Astrophysical Journal)

   The magnetic breakout model explains a variety of solar eruptions, ranging from small-scale jets to large-scale coronal mass ejections (CMEs). Most of our previous studies are focused on jets and CMEs in single null-point topologies. Here, we investigate the initiation of CMEs and associated particle acceleration in a double null-point (or nested fan-spine) topology during multiple homologous M- and X-class flares from an active region. The initiation of the flare and associated eruption begins with inflow structures moving toward the inner null of the closed fan-spine topology. Simultaneous slow flare reconnection below a small filament formed a hot flux rope along with expansion of the overlying flux during slow breakout reconnection at the inner null. The first explosive breakout reconnection of the flux rope at the inner null produced a circular and a remote ribbon along with successful eruption of the flux rope and associated fast EUV (shock) wave. Simultaneous flare reconnection beneath the erupting flux rope produced a typical two-ribbon flare along with two hard X-ray footpoint sources. When the flux rope (with shock) reaches the outer null, a second explosive breakout reconnection produces another large-scale remote ribbon. The radio observations reveal quasiperiodic Type III bursts (period = 100 s) and a Type II burst during the breakout reconnection near the inner and outer nulls, along with gradual solar energetic particles observed at 1 au for magnetically connected events. This study highlight the importance of two successive breakout reconnections in the initiation of CMEs in nested-null topologies and associated particle acceleration and release into the interplanetary medium. The particles are accelerated by the shock ahead of the flux rope, which formed during the inner breakout reconnection. These findings have significant implications for particle acceleration and escape processes in multiscale null-point topologies that produce jets and CMEs. 

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4. Manipulating the direction of turbulent energy flux via tensor geometry in a two-dimensional flow

   https://doi.org/10.1126/sciadv.adv0956  

   Si, Xinyu; De_Lillo, Filippo; Boffetta, Guido; Fang, Lei (July 2025, Analytical science advances)

   In turbulent flows, energy flux, the cornerstone of turbulence theory, refers to the transfer of kinetic energy across different scales of motion. The direction of net energy flux is prescribed by the dimensionality of the fluid system: Energy cascades to smaller scales in three-dimensional flows but to larger scales in two-dimensional (2D) flows. Manipulating energy flux is a formidable task because the energy at any scale is not localized in the physical space. Here, we report a theoretical framework that enables control over energy flux direction. On the basis of this framework, we conducted experiments and direct numerical simulations, producing a 2D turbulence with forward energy flux, contrary to classical expectations. Beyond theory, we discuss how our theoretical framework can have profound applications and implications in natural and engineered systems across length scale ranges from 10⁻³to 10⁶meters, including enhanced mixing of microfluidic devices, biologically generated turbulence, breaking persistent coastal transport barriers, and ocean energy budget. 

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5. Coherent mode and turbulence measurements with a fast camera

   https://doi.org/10.1063/5.0219330  

   Bartolo, Gustavo E; Yadav, Sonu; Fitz, Chloelle; Scime, Earl E (September 2024, Review of Scientific Instruments)

   This study employs a fast camera with frame rates up to 900,000 fps to measure the transfer of energy across spatial scales in helicon source plasmas and during flux rope mergers and the measurement of azimuthal mode structures in helicon plasmas. By extracting pixel-scale dispersion relations and power spectral density (PSD) measurements, we measure the details of turbulent wave modes and energy distribution across a broad range of spatial scales within the plasma. We confirm the presence of drift waves in helicon plasmas, as well as the existence of strong dissipation regions in the PSD at electron skin depth scales for both helicon and flux rope merger experiments. This approach overcomes many limitations of conventional probes, providing high spatial and temporal resolution, without perturbing the plasma. 

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