Papers

In the pursuit of steady-state fusion energy, Advanced Tokamak regimes rely on Internal Transport Barriers (ITBs) with reversed magnetic shear. While Resonant Magnetic Perturbations (RMPs) are commonly applied to control Edge Localized Modes (ELMs) by intentionally making the plasma edge chaotic, the RMPs can also affect the reversed-shear cores. To address this compatibility, we propose a new, adjustable analytical model for plasma current that explicitly incorporates the core, ITB, and edge pedestal components. By applying this current formulation to a Hamiltonian map, we compare how easily magnetic chaos reaches the core in ITB-driven reversed-shear (Non-Twist) plasmas. We find that the localized ITB current creates "twin" inner resonances and pushes outer magnetic island chains closer to the edge. These results highlight a critical operational trade-off: while the Non-Twist topology makes ELM control easier at lower coil currents, it severely shrinks the safety margin against a complete, RMP-induced loss of global confinement.

Families of explicit analytic solutions of the magnetohydrodynamic equilibrium equations are presented, equivalent to steady incompressible Euler flow. The solutions are non-axisymmetric and possess exact nested toroidal flux surfaces. No expansion is made in inverse aspect ratio or in the deviation from axisymmetry. The magnetic field and flux surfaces are given explicitly in Cartesian coordinates using elementary functions. The field, current density, and scalar pressure are smooth over the toroidal domain. The pressure gradient vanishes only on the magnetic axis. One family of solutions has uniform rotational transform $\iota=2$, while another family has a sheared $\iota$ profile. These counterexamples to Grad's conjecture are valuable for understanding the existence and regularity of 3D equilibria and for testing numerical codes.

Parker Solar Probe, near its 23rd perihelion in March 2025, sampled an extended interval of sub-Alfvénic solar wind likely originating from a large equatorial coronal hole. At heliocentric distances of approximately 10 solar radii, with speed mostly above 400 km/s, this interval is a first example of “polar coronal hole-like (PCH-l) fast" solar wind observed in the sub-Alfvénic solar corona. We characterize the turbulence properties of this unique interval using Parker Solar Probe measurements. Despite being sampled well inside the nominal Alfvén surface, the turbulence appears to be already well developed while remaining strongly transverse and highly imbalanced, exhibiting a large cross helicity. These observations provide new constraints on the development and evolution of solar wind turbulence within the lower corona.

We demonstrate a laser-wakefield accelerator driven by a high-repetition-rate optical parametric chirped-pulse amplification (OPCPA) laser, producing stable, quasi-monoenergetic electron beams at 100 Hz. Using 70 mJ, 8.1 fs laser pulses, we obtain 47 MeV electron beams with 15 pC charge and an intrinsic energy spread below 10%. Measurements over 10,000 consecutive shots show rms fluctuations of only 1.4% in peak energy and 12% in charge, together with low pointing jitter. Principal-component analysis reveals that the beam fluctuations are described by five physically interpretable modes, dominated by slow variations below 1 Hz. Particle-in-cell simulations reproduce the measured spectrum and show that nonlinear self-focusing localizes ionization injection, resulting in the observed narrow energy distribution. The demonstrated combination of electron energy, charge, beam quality, and stability represents a significant step toward high-average-power laser-plasma accelerators.

We propose a two-stage production method to overcome existing supply-constraints for the alpha-emitter $^{149\mathrm{g}}$Tb, a promising candidate for Targeted Alpha Therapy (TAT) with no existing globally scalable production pathway. Although awaiting experimental measurement of the $^{150}$Gd(p,2n)$^{149\mathrm{g}}$Tb cross section, the proposed method could produce $^{149\mathrm{g}}$Tb at clinical scale and beyond on readily available proton cyclotrons, enabled by production of the extinct but long-lived isotope $^{150}$Gd, a pure alpha emitter with a 1.79 million year half-life. Stage one generates $^{150}$Gd feedstock by irradiating natural Eu or enriched $^{151}$Eu with $\gtrsim$10 MeV protons, neutrons or photons. Stage two produces $^{149\mathrm{g}}$Tb from fabricated $^{150}$Gd targets by driving the $^{150}$Gd(p,2n)$^{149\mathrm{g}}$Tb reaction with $\gtrsim$14 MeV protons, accessible on over 700 reported cyclotrons worldwide. Fast fusion neutrons appear to offer the most scalable pathway for $^{150}$Gd production: even with a large $^{149 \mathrm{g}}$Tb dose size of 1 GBq and 40 million administered doses/yr, we estimate this would require neutrons produced by only 6.8 megawatts of steady-state deuterium-tritium power to produce the required $^{150}$Gd, far below expected capacity in the next decade. The route described here, if validated, would enable $^{149\mathrm{g}}$Tb supply at the scale needed to support clinical development of $^{149\mathrm{g}}$Tb-based TAT.

Sheet-like structures are ubiquitous in magnetohydrodynamic systems and are known to play a crucial role in astrophysical plasma transport. Here, by applying a theoretical framework to data from numerical simulations, we demonstrate that current-sheet formation is a direct consequence of energy conversion between kinetic and magnetic fields. The strain-magnetic field organisation associated with this conversion favours the emergence of sheet-like structures, and analytical calculations show that sheet-like geometry constitutes the dominant flow configuration. We further show that the same conversion-driven reorganisation of the strain motion is responsible for the depletion of the mean Inertial energy transfer, a previously observed phenomenon whose physical origin has remained unclear. Finally, we identify experimentally accessible diagnostics through which these predictions can be tested in multi-spacecraft observations of turbulent plasmas.

In a tetrad formulation of general relativity, an ideal Ohm-type condition for the gravitational field implies the conservation of gravitational fluxes and the preservation of the connectivity of gravitational field sheets. We investigate the consequences of departures from ideal gravitational evolution by developing a theory of gravitational reconnection, defined as a change in the connectivity of gravitational field sheets arising from the breakdown of the ideal frozen-in evolution of the gravitational field. We derive quantitative measures of the gravitational reconnection rate, show that gravitational reconnection alters the energy-momentum exchange between the gravitational and matter sectors, and determine how it modifies the evolution of gravitational helicity. Our results provide a quantitative framework for describing changes in gravitational connectivity and their consequences in dynamical spacetimes.

Spacetime can undergo complex nonlinear evolution, as governed by the Einstein field equations, and a central challenge is to understand the geometric structures that arise, persist, and interact throughout its evolution. Using a formulation of Einstein equations that parallels nonlinear electrodynamics of continuous media, we show that general relativity admits gravitational field connections—two-surfaces and associated field lines whose connectivity is maintained by the spacetime dynamics. This gravitational frozen-in behavior is enabled by an ideal Ohm-type condition for the gravitational field. We further show that the same framework naturally leads to a conserved “gravitational magnetic” flux. A conserved gravitational helicity also emerges, with a clear topological interpretation in terms of gravitational field-line structures. These results identify well-defined topological constraints on admissible spacetime evolution and provide an organizing principle underlying the nonlinear dynamics of spacetime.

Low-luminosity accretion disks around black holes are weakly collisional, potentially enabling nonthermal particle acceleration. Local two-dimensional particle-in-cell simulations of the stratified magnetorotational instability (MRI) in pair plasmas by Sandoval et al. (2024; hereafter S24) revealed nonthermal populations with maximum energies proportional to the scale-separation ratio $\omega_{c,0}/\Omega_0$, where $\omega_{c,0}$ and $\Omega_0$ are the initial particle cyclotron and Keplerian frequencies, respectively. We identify the acceleration mechanisms involved and quantify their scale-separation dependence. Acceleration occurs primarily within large-scale current sheets associated with an MRI dynamo. Particles are initially injected by non-ideal electric fields during reconnection driven by plasmoid splitting, attaining energies independently of scale separation. They subsequently undergo rapid first-order Fermi-like acceleration occurring within converging flows between newly formed, separating plasmoids. During this stage, energies grow at a rate proportional to the instantaneous non-relativistic cyclotron frequency, independently of $\omega_{c,0}/\Omega_0$. This fast acceleration rate implies a maximum energy proportional to $\omega_{c,0}/\Omega_0$. Particles then continue interacting repeatedly with plasmoids, undergoing slower, predominantly second-order Fermi acceleration, with a subdominant contribution from shear acceleration. This stage increases particle energies by only a factor of a few over several orbits, regardless of $\omega_{c,0}/\Omega_0$. The combination of these three stages implies a maximum energy proportional to $\omega_{c,0}/\Omega_0$, explaining the scaling found by S24 and suggesting that the MRI may accelerate particles to ultrarelativistic energies in low-luminosity disks. Testing these results in three dimensions remains an important next step.

Coronal streamer kink waves excited by an impact of coronal mass ejections (CMEs) are routinely used to estimate the coronal Alfvén speed. These estimates generally assume wave propagation parallel to the equilibrium magnetic field directed radially outward to the Sun, in the plane of the sky. However, the geometry of CME impacts naturally allows for oblique propagation. We investigate the properties of obliquely propagating kink waves guided by a plasma slab with a central current sheet representing a coronal streamer stalk. We consider both cold and warm streamer plasmas and analyse influence of propagation obliquity on wave dispersion, eigenfunctions, and seismological diagnostics. We find that increasing the propagation obliquity reduces the phase speed owing to both projection effects and the intrinsic dependence of the phase speed on the propagation angle. The wave structure also undergoes a gradual transition from a body mode to a surface mode, leading to stronger perturbations at the slab boundaries and enhanced wave localization. Consequently, for a given energy deposited by a CME impact, oblique kink waves are expected to produce larger observable amplitudes than field-aligned waves. Applying the developed theory to streamer waves reported previously, we infer Alfvén speeds in the range of 50-500 km/s. We show that neglecting wave propagation obliquity may underestimate the Alfvén speed by up to a factor of 1.5. These results demonstrate that wave propagation obliquity should be taken into account in coronal seismology of streamer waves and that stereoscopic observations will be required to constrain the true propagation direction.

Reliable disruption prediction is essential for the safe operation of future tokamaks. Existing full-distribution survival methods model the complete residual time-to-disruption distribution, whereas operational decisions primarily depend on disruption risk within a finite prediction horizon. This mismatch motivates introducing Early Event Prediction (EEP) objectives into survival-based disruption prediction. We take Deep Survival Machines (DSM) as the full-distribution baseline and propose applying two established EEP methods to tokamak disruption prediction: Temporal Label Smoothing (TLS), which directly predicts disruption probability within a finite horizon, and survTLS, which additionally models the event-time distribution within that horizon. Using a common causal encoder, we compare these methods on DIII-D, Alcator C-Mod, and EAST. We distinguish threshold-free deadline ranking from validation-selected fixed-policy alarm performance and evaluate prediction horizons and encoder architectures. TLS achieves the best mean alarm performance on DIII-D and EAST, whereas all methods perform poorly on Alcator C-Mod. survTLS does not consistently outperform DSM, suggesting that directly learning horizon-level event probability is more effective than modeling detailed within-horizon event-time distributions in the present setting. Finally, the selected prediction horizons and encoder-ablation results vary across devices, reflecting differences in disruption characteristics.

Electronic entropy is usually treated as a secondary correction to structural stability, but under strong electronic excitation it can become a primary thermodynamic driving force. Here we show that electronic entropy can drive both polymorphic and stoichiometric phase transformations in compressed iron oxides. Using finite-temperature density functional theory, we calculate the electronic-temperature-dependent Gibbs free energies of Fe$_2$O, FeO, Fe$_4$O$_5$, Fe$_3$O$_4$, and multiple Fe$_2$O$_3$ polymorphs, including $\alpha$-, $\iota$-, $\zeta$-, $\eta$-, and $\theta$-Fe$_2$O$_3$, over the pressure range 60–260 GPa. At 60-140 GPa, electronic excitation mainly reorganizes the relative stability of Fe$_2$O$_3$ polymorphs, driving transitions from $\iota$-Fe$_2$O$_3$ to $\eta$-Fe$_2$O$_3$. At 180 GPa, the free-energy landscape becomes strongly competitive as FeO is stabilized over an intermediate range of electronic temperature, while $\eta$-Fe$_2$O$_3$ becomes favourable at higher T. At 220-260 GPa, the lowest-free-energy phase at low T is the Fe-rich compound Fe$_2$O, but increasing electronic temperature stabilizes FeO. These results demonstrate that electronic entropy can control not only the relative stability of crystal structures at fixed composition, but also the competition between different iron-oxide stoichiometries. The predicted electronic-entropy-driven phase boundaries provide a route to nonthermal structural transformations in ultrafast and high-energy-density experiments.

This paper is devoted to the derivation of the dispersion relation of the Geodesic Acoustic Mode in pair plasmas, i.e. assuming that ions and electrons have the same mass. Geodesic Acoustic Modes are plasma perturbations playing a crucial role in turbulence regulation, and therefore in the determination of the plasma confinement in tokamaks. Experiments with pair plasmas, like electron-positron plasmas, have been proposed with different kinds of confinements, and aim to study fundamental processes in plasma physics and understanding the formation of the early universe.

A self-consistent treatment of strong-field laser - plasma interactions suggests a heuristically valuable extension of the notion of nonlinear-optical susceptibility to perturbative regimes of stimulated light scattering in plasmas, offering powerful insights into stimulated-scattering-induced cross-beam energy transfer processes. These findings lay grounds for a unified treatment of stimulated light scattering across a vast area of optical physics, spanning from fiber optics and neutral gases to laser - plasma physics.

We employ equation-driven, physics-constrained deep learning to solve the fixed-boundary Grad-Shafranov (GS) equilibrium problem, constructing axisymmetric magnetohydrodynamic equilibria with tokamak-relevant characteristics. Equilibria across linear (Solov'ev) and nonlinear profile functions are constructed using Physics-Informed Kolmogorov-Arnold Networks (KANs) that approximate GS solutions while satisfying appropriate boundary conditions. A highly nonlinear pressure profile recreating high-confinement mode phenomenology, such as pressure pedestals and significant bootstrap current components, is also considered. To enable efficient convergence, guided training schemes are employed, specifically homotopy-based continuation curriculum learning and transfer learning via pretrained networks. While computing nonlinear equilibria employing standard Multi-Layer Perceptrons under unguided physics-informed training remains an elusive or computationally inefficient task, our framework overcomes this limitation. Specifically, we demonstrate that the combination of three key elements, namely KAN architecture, guided training schemes, and the self-scaled Broyden optimization method, enables stable, efficient, and accurate equilibrium computation with simultaneous profile parameter identification in view of equilibrium constraints.

Radiation drag from inverse-Compton scattering of an external radiation field changes the acoustic dispersion relation of a relativistic fluid. We derive the linear dispersion relation and show that, depending on the electron distribution and fluid sound speed, radiation drag either damps both modes or damps one while driving the other unstable. The unstable growth is robust at short wavelengths but slow and overdamped at long wavelengths, where the linear analysis is limited by the background acceleration. The resulting growth and damping rates are of order the bulk radiative acceleration rate, so whenever radiation drag is important for the background flow, its effects on fluid perturbations are also important. A purely damped region exists for a wide range of parameters. Radiation drag also makes acoustic waves dispersive: The phase speed deviates from the ordinary sound speed at longer wavelengths, and approaches the sound speed at short wavelengths. We validate the derived rates using special-relativistic hydrodynamic simulations. We apply the derived relation to astrophysical jets such as gamma-ray bursts, blazars in the broad-line region of the host active galactic nucleus, and quasar jets traveling through the CMB and galactic radiation field. We find that the derived instability, damping and dispersion may be relevant across a range of relativistic outflow conditions.

Plasma transport produced by electrostatic fluctuations is studied using a test particle model in a toroidal geometry. A model wave spectrum is assumed which introduces a time dependence in the Hamiltonian description of particle motion in the strong magnetic field. This allows for the existence of chaotic particle motion which gives rise to transport processes. Another way of producing transport is by introducing a stochastic process inside the wave spectrum. The two possibilities are explored and it is shown that both cases give rise to diffusive transport. The presence of chaotic motion is corroborated by computing approximate Lyapunov exponents. Additionally the presence of zonal flow is considered which can give rise to a transport barrier by suppressing radial particle fluxes, in the cases that show chaotic transport. This effect gives support to the existence of chaotic motion as responsible for transport since it reproduces the behavior of the robust invariant torus resilience to chaos, acting as a transport barrier, observed in Hamiltonian models of chaos.

A rigorous implementation of energy-dependent ion- and electron-induced electron emission in a continuum-kinetic framework is used to reveal their effects on the scaling of plasma properties in the sheath with an applied bias potential to the walls. The approach comes with a novel methodology for modeling particle-induced electron emission (PIEE) that includes 1) improved fitting functions for the yield and spectra, 2) the use of SRIM and a summation of the Lindhard formula and a modified Bethe formula for obtaining accurate stopping powers, and 3) a binding energy correction to the PIEE spectra and ion-induced yield based on density functional theory (DFT) calculations. The emission models are implemented as a fully energy dependent and dynamic boundary condition. For this investigation, tungsten and graphite walls are studied for their relevance in magnetic fusion experiments. Equations are derived from fluid theory that predict the relative importance of ion- and electron-induced emission on the structure of the sheath. The simulations provide evidence for the theoretical predictions, showing that a transition from a classical to space-charge limited (SCL) sheath depends primarily on electron-induced emission. Furthermore, claims in previous literature of increased heat and particle loads to the walls due to electron emission are supported, however differing mechanisms for the increase are observed. The increased thermal and particle fluxes due to PIEE are primarily driven by collisional transfer of energy from emitted electrons in the presheath. Finally, quantitative predictions for the device modeled in this study coincide with previous modeling efforts and experimental measurements.

Exponential potentials were used since Kramers, Hellman, Glauberman, Yukhnovskii and Kelbg for solving problems of quantum chemistry, ionic solutions and plasmas. Here we develop the theory further and add new results, in particular with respect to the quantum-statistical theory. In particular, we derive the Kelbg quantum potential for the exponential interactions and discuss screening as well as the problem of thermodynamic stability. Further we give new applications to a qualitative theory of alkali plasmas and fusion plasmas. We show that the exponential potential and the early analytical results of Yukhnovskii and Kelbg allow a qualtative analytical treatment of such difficult problems as the phase transitions in electrolytes and alkali plasmas.

We investigate whether the plasma disturbances generated by a charged debris object can be used to infer its position without directly sampling the object or its immediate sheath. A one-dimensional open-boundary electrostatic particle-in-cell (PIC) framework is used to model a continuously flowing electron-ion plasma containing an initially uncharged debris object. The debris charges self-consistently and produces an ion-ion counter-streaming instability (IICSI), which is sustained and reaches a statistically stationary state. A matching simulation without debris provides a controlled background against which debris-induced changes in different plasma fields are identified. The precursor and wake are examined through their spatial extent, fluctuation power, and frequency–wavenumber spectra. Weak-form sparse regression is then used as a supporting tool to recover reduced fluid and kinetic residuals and to learn an empirical relation connecting the precursor and wake disturbance envelopes to the equilibrium plasma flow, debris charge, and distance from the source. The predictive capability is examined by successively treating each simulation as an independent case. For each evaluation, the model is constructed from the remaining simulations, while the excluded simulation is used only to infer the debris position from its plasma response. For the idealized cold-ion regime considered here, the procedure successfully localizes the debris in transonic and supersonic flows, whereas the subsonic cases remain unresolved. These results demonstrate that debris-induced plasma disturbances possess a learnable spatial structure and provide a proof-of-principle route toward future remote localization using more realistic multidimensional models; they do not constitute an operational debris-detection scheme.

We present a machine-learning-accelerated plasma simulation scheme that combines learned time jumps with ordinary physics evolution. A neural network corrects a low-cost physics forecast over multiple time steps, while the original solver reconstructs the state and advances it between jumps through short reanchoring intervals. The scheme is implemented in PASCHEN-1D, a one-dimensional drift-diffusion-Poisson solver, achieving up to $4.70 \times$ CPU rollout speedup relative to the ordinary solver for nanosecond pulsed nitrogen discharges. The simulations capture pre-breakdown evolution, rapid sheath formation, expansion and collapse under pulsed-voltage excitation, and post-pulse afterglow. Bulk densities and electric fields agree closely with the ordinary-solver reference, while cathode sheath width, gap voltage, and discharge current reproduce the principal temporal features. The largest spatial discrepancies occur in the cathode sheath during fast transients. A sweep of the physics-reanchoring duration reveals a trade-off between accuracy, acceleration, and numerical stability over the tested 500 ns simulation interval. A model trained on simulations with 1000 grid points also shows useful transfer to 500- and 1500-point meshes without retraining. These results demonstrate a practical route to accelerating plasma simulations by augmenting an established physics solver with machine learning.

Tokamak equilibria are commonly exchanged as gridded G-EQDSK files whose conventions, resolutions, and machine-specific formats impede cross-device comparisons and data-driven modeling. Here, we present VEQDB, an open, compact, and reconstructible fixed-boundary equilibrium database built on continuous MXH–Chebyshev geometry and independent physical-profile roots. By decoupling authoritative equilibrium physics from rectangular meshes, VEQDB enables continuous evaluation and metric differentiation at arbitrary application-demanded resolutions. Backed by an automated numerical validation pipeline, VEQDB is structured as an extensible repository for ongoing community expansion. Its inaugural release provides 13,291 accepted equilibria across 267 conventional and spherical tokamaks, encompassing parameter-sampled Grad–Shafranov solutions, G-EQDSK projections spanning EAST, MAST-U, and ITER scales, and controlled variation families with explicit provenance. Benchmark projections reproduce normalized flux maps with RMS errors between $1.09 \times 10^{-3}$ and $1.45 \times 10^{-3}$, while compact JSON representations achieve an 89–96-fold size reduction relative to standard $129 \times 129$ G-EQDSK files. The complete initial release occupies 41~MB in raw JSON and 18~MB in compressed archives, and all records successfully passed independent reload and evaluation tests. VEQDB establishes an extensible, provenance-preserving foundation for equilibrium studies, reduced-order surrogate modeling, and cross-machine workflows.

We extend the Obukhov-Corrsin theory of scalar turbulence to compressible flows with spatially variable, anisotropic diffusivity. Combining density and diffusivity into a single positive matrix field, a transport landscape, permits an exact scale-by-scale balance in which the sign-indefinite commutator between filtering and diffusion is eliminated rather than estimated. If the density-weighted third-order velocity and scalar increments scale as $\ell^\alpha$ and $\ell^\beta$, respectively, we prove that anomalous scalar dissipation is impossible when $\alpha+2\beta>1$. Remarkably, this threshold is independent of the anisotropy and spatial regularity of the diffusivity, provided it remains uniformly elliptic. Codimension-one shocks in both velocity and scalar have $\alpha=\beta=1/3$ and therefore lie exactly at the critical threshold. For statistically stationary turbulence we further obtain an exact density-weighted constant-flux relation, providing a compressible analogue of the relation underlying Yaglom's law. The results apply directly to passive-scalar transport in both gases and magnetized plasmas and provide testable diagnostics for simulations of compressible magnetohydrodynamic turbulence. Because the same operator governs anisotropic heat conduction, the results carry over to the electron temperature of a magnetized plasma, and they imply that gradient statistics in such flows must be contracted with the transport landscape rather than with the density.

Real time plasma state estimation for control of Tokamak devices are challenging due to the stringent latency requirements of the plasma control system (PCS). We present an end-to-end workflow for deploying a recurrent probabilistic neural network (RPNN) on FPGA hardware. We combine architecture size reduction with quantization-aware training via QKeras. The model is then synthesized using hls4ml, targeting a Xilinx Alveo U50 device. We report a design that fits comfortably within all four resource budgets (DSP, LUT, FF, BRAM) at deterministic sub-10~$\mu$s single-timestep latency, meeting the requirements for real-time inference inside a model-predictive-control-style plasma control loop.

We resolve an existing question concerning dynamical and structural stability of the E {\times} B staircases in magnetically confined fusion plasma. The problem has stirred considerable interest in the literature due to a unique combination of its scientific and practical aspects. Here, we report a new approach to the problem by combining the paradigmatic Hasegawa-Wakatani model of electrostatic drift-wave turbulence with an idea of interaction renormalization, imported from quantum field theory. It is shown based on the Schrödinger-Newton equation with renormalized interaction constant that the plasma staircase is robust and stable as soon as the nonadiabaticity parameter, {\delta}, goes above a certain critical value, and is unstable otherwise. This critical value is an exact result of the interaction model and is found to be {\delta}c = {\pi}. For {\delta} < {\delta}c , the unstable system expands in the radial direction, resulting in a radial second moment that grows with time t as t^(2/3). The results obtained bear important implications with regard to the implementation of arrays of semipermeable transport barriers in tokamaks, suggesting a threshold condition for their generation.

A species-specific weighting scheme for the Natural-Sample-Size collision model within the Direct Simulation Monte Carlo method is developed and implemented in the open-source gas and plasma solver PICLas. The implemented weighting scheme places particular emphasis on chemical reactions and ionization processes of trace species in order to guarantee physically accurate and low-noise simulations of atmospheric entry processes. The successful implementation and the conservation of momentum and energy during relaxation processes and chemical reactions are verified through a reservoir simulation of a reacting air mixture. As a more sophisticated validation case, atmospheric entry simulations of a cylinder at an altitude of 108 km are investigated. In a final step, the developed weighting scheme is employed to investigate ionization processes in the shock layer surrounding the RAM-C II reentry probe during atmospheric entry. The simulations showed very good agreement with experimental flight data and reduced noise in the rarefied regions for the charged species.

A set of experiments on merging dynamics of localized magnetized plasma pressure filaments in close proximity has been carried out in a large linear magnetized plasma device. A two filament configuration is used to determine the separation scale of cross-field interaction. Fluctuation analysis of the ion saturation current confirms the presence of unstable drift-Alfvén modes on each filament which are predominantly driven by the steep electron temperature gradient. When the filaments are separated a distance of approximately five times the size of a single filament or greater, no interaction is observed and the drift-Alfvén modes remain uncoupled. When brought closer together, significantly stronger interaction occurs with transfer of charge and energy, leading to the generation of inter-filament electric fields. This has the effect of rotating the filaments and influencing the merging dynamics. When the filaments are asymmetrically heated, the cooler filament becomes wrapped around the other, and the drift-Alfvén modes become fully coupled in a global mode structure. Transport between the filaments is explained in terms of E x B drift and the local potential wells of the filaments, and drift-Alfvén mode coupling occurs when the filaments are brought within the distance of a collisionless skin depth.

Solar wind protons exhibit a temperature anisotropy that deviates from the double-adiabatic prediction, suggesting an additional energy source. To investigate solar wind heating mechanisms, we analyze Helios 1 and 2 data and characterize the radial evolution of the adiabatic invariants and anisotropic heating rates of fast wind protons, considering both the bulk population and its core and beam components separately. Unlike previous studies, we account for proton heat fluxes and deviations from the Parker spiral caused by large-amplitude fluctuations, which causes significant differences in the parallel heating rates compared to earlier results. Although earlier work has questioned the reliability of power laws to estimate heating rates and proposed as a more robust approach the investigation of the radial evolution of adiabatic invariants, we show that the two approaches yield consistent results when applied to the same dataset. Our analysis shows that all proton populations considered require net perpendicular heating, consistent with earlier studies. In contrast, the parallel energy evolution differs between populations. Core protons require parallel heating, whereas beam protons undergo parallel cooling although the total proton population undergoes a net parallel cooling. This behavior is consistent with the combined action of turbulence and core-beam kinetic instabilities, which together can drive preferential perpendicular heating while simultaneously produce parallel cooling in the fast solar wind. Core proton parallel heating could instead be a signature of Alfvén wave decay.

An efficient Particle-in-Cell numerical approach to perform full-dimensional kinetic simulations of low temperature plasmas is presented. Taking advantage of the cylindrical geometry of most plasma sources, a Fourier mode decomposition of the fields is carried out in the azimuthal ($\theta$) direction up to a chosen maximum number of modes $N_m$. Macroparticles are pushed in all $D$ dimensions and weighed, for each mode $m$, onto a $(D-1)$ dimensional grid. The computation of the electric field for each mode is independent and reduces to solving $(N_m+1)$ $(D-1)$ dimensional Poisson problems. The approach brings spectral accuracy in the azimuthal direction, while the computational cost is comparable to that of a simulation with $(D-1)$ dimensions. We verify this approach against a planar test case based on a Penning discharge, widely used for benchmarking and validation purposes in the low-temperature plasma community. Our approach allows us to reduce the 2D problem into a collection of coupled 1D problems and to naturally perform spectral analysis of the different azimuthal modes, recovering the contribution of each mode to radial transport, with a computational time saving of one order of magnitude with respect to state of the art 2D particle-in-cell codes.

We present a formulation of general-relativistic (GR) 19-moment dissipative magnetohydrodynamics (MHD), capable of handling all first-order dissipative terms (viscosity, heat conductivity, resistivity and Hall terms), as well as all ideal electron degrees of freedom (number density, momentum and energy) in a GR astrophysical two-fluid plasma. We derive necessary and sufficient nonlinear causality conditions for the constrained first-order 19-moment system, as well as both necessary and sufficient conditions for strong hyperbolicity. To assess the formulation numerically, we develop a high-resolution shock-capturing scheme that solves these equations in a performance-portable fashion. The scheme expresses all evolution equations, including the dissipative and electron sectors, in flux-divergence form, allowing us to model systems with scales separated by orders of magnitude without resolving kinetic scales everywhere on the grid. In addition, we use implicit integration methods to systematically overstep kinetic scales in MHD regions, such as cyclotron and plasma frequencies. To make the scheme as robust as GRMHD codes, we construct necessary and sufficient conditions for a conserved state to be physically admissible, and based on these construct a new physicality-enforcement scheme. As an exact validation comparison, we formulate and derive a full solution to dissipative two-fluid Bondi accretion in general relativity. We then validate the equations against a series of results from kinetic particle-in-cell models of black hole accretion and magnetospheric dynamics, demonstrating that our formulation and scheme can correctly capture major features relevant for feedback on global scales of these solutions, including dimensionless reconnection rates of order $0.1$ and Braginskii-like anisotropic pressures and heat fluxes.