20,325 papers in this slice of arXiv.
Richard Fitzpatrick
The macroscopic ideal-MHD stability of an axisymmetric mirror device with sonic levels of plasma rotation is analyzed by approximating the plasma equilibrium as a rotating theta pinch possessing an artificial gravity. An eigenmode equation is derived that governs the stability of the equilibrium to small perturbations in the case of an arbitrary plasma angular velocity profile. The stability of the m=1 and m=2 modes is investigated. The plasma is found to be stable to these two modes provided that it is sufficiently short in the axial direction. The critical axial length of the device below which the modes are stabilized first decreases with increasing plasma rotation, attains a minimum value when the rotation is roughly sonic, and then increases with increasing plasma rotation. The value of the plasma rotation off the magnetic axis is found to have a significantly stronger effect on the stability of the modes than the value on the magnetic axis.
S. Shiber, P. Hoeflich, T. Mera +9
Type Ia supernovae (SNe Ia) explosively destroy carbon-oxygen white dwarfs (WDs) in multiple stellar systems. They produce approximately 50% of the iron-group elements in the Universe, synthesize electron-capture (EC) elements, drive nuclear physics experiments, and underpin high-precision cosmology. To first order, the outcome is governed by nuclear physics, a property often described as stellar amnesia. Recently, this stellar amnesia has begun to be broken by the nearly universal detection of EC elements with JWST. These elements trace high-density burning, largely ruling out the currently popular helium-triggered, sub-Mch detonation models as the dominant channel. Instead, the ubiquitous presence of EC is shifting back the focus to dynamical and secular mergers, and near-Mch explosions similar to the deflagration model W7, but in which the nuclear flame undergoes a deflagration-to-detonation transition. The early deflagration phase is especially important because spherical simulations identify the central WD density, and thus the WD mass, as a key parameter governing the explosion. Here, we present detailed magneto-hydrodynamical simulations. We find that small-scale, pre-existing turbulence expected from the pre-explosion smoldering phase is essential for overcoming the fundamental challenges imposed by the intrinsic 3D physics. This turbulence systematically reduces the production of EC elements by about a factor of two, implying the need for WD central densities closer to those associated with accretion-induced collapse to a neutron star. We also demonstrate the effect of magnetic fields near the saturation field strength and highlight the need for higher-precision EC rates at low Ye.
Qinghao Shen, Cas van Deursen, Pieter Willem Groen +2
In this work, a three-dimensional computational fluid dynamics model is developed for a vortex-stabilized microwave CO2 plasma reactor operating over the pressure range of 100-400 mbar. The model combines experimentally constrained, emission-based plasma sizes and volumetric heat-source distributions with thermally dominated finite-rate heavy-particle chemistry for a multi-component mixture. Turbulent flow and transport are described using the SST k-omega model. The model reproduces the measured radial gas-temperature profiles in the plasma core and the non-monotonic pressure dependence of CO2 conversion, including a maximum at 150 mbar and a pronounced decrease at 400 mbar. A vortex-driven recirculation region redistributes gas upstream. Turbulent mixing and cooling are strongest near the upper reactor boundary, but their contribution decreases as pressure increases. The pressure dependence of conversion is determined by the competition between CO2 dissociation and CO recombination. CO2 direct dissociation reaction dominates in the high-temperature plasma core, whereas O-assisted conversion reaction contributes near the plasma edges and in the surrounding hot region. At 150 mbar, enhanced CO2 dissociation is accompanied by limited CO loss, resulting in the highest conversion. With pressure increasing to 400 mbar, slower cooling and more frequent three-body collisions promote CO recombination in the afterglow, causing more than 60% of the CO formed near the plasma to be lost downstream. Moreover, additional CO loss occurs in the upper region of the reactor at higher pressures because of the reduced cooling rate.
M. Pelkner, K. Hallatschek
In previous work, we introduced a semi-analytical method for computing time-domain solutions of linearized Vlasov problems. Rather than representing the plasma response as a sum of residues associated with Landau poles, the method constructs a regularized frequency-domain response spectrum that is subsequently inverted numerically. Explicit applications have so far been limited to unmagnetized plasmas. In this work, we extend the construction to plasmas with a uniform background magnetic field and a Maxwellian equilibrium distribution. We apply the resulting formulation to the electrostatic ion-Bernstein density response of a plasma with kinetic ions and adiabatic electrons, and provide error estimates for truncating both the spectral integration domain and the cyclotron-harmonic expansion. The solution serves as a time-domain reference for damped finite-k∥ regimes, in which dispersion-relation roots alone are insufficient for pointwise-in-time verification of simulation codes. Finally, we indicate how the framework can be extended to fully electromagnetic problems.
J. F. Parisi
Nuclear batteries powered by alpha decay have been deployed successfully for over 60 years, on a worldwide 238Pu supply of kilograms per year. We show that the 14 MeV neutrons of a single deuterium-tritium fusion plant can produce alpha emitter battery fuels up to tons per year, in three classes: fuels with completely new production pathways (236Pu, 227Ac, 210Pb), fuels previously proposed whose scarce feedstock the same pathways now breed at scale (232U, 228Th), and the established 238Pu. OpenMC simulations of actinide channels in a tokamak blanket give, per GW yr of fusion: 11 to 57 kg of 236Pu, whose chain releases 18 GJ per gram over a century, ending at stable 208Pb, plus up to 5.2 t of co-product 238Pu; up to 1.4 t of 231Pa from thorium, and, from channel with 231Pa feedstock, up to ∼15 t of 232U or ∼122 kg of 210Pb, with 227Ac produced at 21 g/yr per tonne of 231Pa. Neutron capture also upgrades 241Am to a 242Cm/242mAm/241Am/238Pu blend with up to 10 times higher power density. The same 236Pu and 232U also serve as proliferation safeguards: the 237Np, 232Th, and 231Pa channel products are self-protecting, the plutonium by 236Pu and 238Pu decay heat and the 2.6 MeV gammas from 208Tl content, and similarly the uranium from its 232U. Many of these fuels (236Pu, 232U, 228Th, 227Ac) have an order of magnitude higher power and energy density than current alpha emitters, and at human spaceflight-relevant doses the 227Ac and 210Pb chains need less shield mass than 238Pu or 241Am above a few hundred watts. Fusion neutrons could therefore enable nuclear batteries at the kilowatt to megawatt scale and unlock new possibilities for power sources requiring exceptionally high energy density.
Immanuel Christopher Jebaraj, Lucas Colomban, Oleksiy Agapitov +7
Diffusive shock acceleration, at shocks from coronal mass ejections to supernova-remnant blast waves, presupposes a scattering wave field that the accelerated particles themselves maintain. This self-regulation has not been resolved in situ. We report Parker Solar Probe observations of a fast (~2800 km/s), near-parallel interplanetary shock at 0.24 AU on 2023 March 13 and separate its upstream wave field into four families, a classification not made before at a fast shock near the Sun. Right-hand and left-hand circularly polarized families over a common wavenumber band, with a field-aligned linearly polarized family, are cyclotron-resonant with the suprathermal-to-MeV protons streaming from the shock: the beam drives the field that scatters it, and the measured mean free path, half the precursor scale, leaves the beam anisotropic enough to sustain the drive. Outside this loop lies a weak, oblique, linearly polarized component, a few per cent of the wave power, resolved here for the first time at an in situ foreshock. Its in-phase density and field-magnitude fluctuations identify the compressive part as fast magnetosonic and shift the cyclotron-resonance energies of the resonant families by up to 13 % along the precursor. Acceleration at shocks inside 0.3 AU is governed upstream, in a foreshock the shock builds for itself.
Jiyuan Chen, Jihoon Kim, Roopendra Singh Rajawat +1
Compact heavy ion accelerators have numerous applications, ranging from heavy ion fusion to carbon ion radiotherapy, and testing radiation-hardened electronics. The demand could be met by developing high-gradient traveling wave plasma accelerators of high-charge (∼μC) relativistic ion beams. We will discuss a novel ion acceleration regime -- Counter-propagating ionization Front Acceleration (CFA) -- utilizing counter-propagating Ionization Front (IF) and high-current Relativistic Electron Beam (REB). Theoretical modeling and 3D PIC simulations demonstrate the possibility of using typical REBs produced by induction voltage adders propagating through a gas-filled tube undergoing laser ionization to achieve acceleration gradients in excess of ∼250MeV/m while accelerating micro-Coulombs of ions over meters distance. A unique energy conversion mechanism -- from the REB to electromagnetic fields to the ions is discussed, as well as the limits on the accelerated ions charge and the degree of its neutralization, acceleration gradient, and ion energy spread.
B. Tripathi, A. E. Fraser, P. W. Terry +3
At every scale they occupy, magnetic fields affect various phenomena, including star formation, cosmic ray transport, charged particle acceleration, space weather, transport in planetary atmospheres, and laboratory plasmas. These fields are often generated and sustained by turbulent flows in a process called the dynamo. In 1955, E. N. Parker parameterized the effects of small-scale turbulence to propose a mean-field dynamo theory. The widely used theory reproduces observed large-scale fields but suffers from difficulty in tuning parameters as they are not justified from first principles: Studies of turbulent flows show tangled magnetic fields, which are folded and fragmented into small-scale structures due to shear-flow straining. Here, considering a shear flow that is unstable and driven, we develop analytic theory and perform three-dimensional (3D), advanced computer simulations of turbulence with up to 4096 x 4096 x 8192 grid points, showing ab initio generation of quasi-periodic, large-scale magnetic fields. The generation occurs via the mean-vorticity effect---an additional mean-field dynamo process postulated in 1990. Crucial to this dynamo is the prior generation of large-scale 3D jets, robustly produced as topologically protected and exact nonlinear solutions of the magnetohydrodynamic equations. The jet-driven dynamo applies to shear-driven laboratory and astrophysical systems. These include binary neutron star mergers, where the reported dynamo likely operates on microsecond timescales to produce in milliseconds some of the strongest magnetic fields in the Universe, providing signals for multimessenger astronomy.
Marisa Petrusky, Iain D. Boyd
Accurate numerical simulation of rarefied hypersonic plasmas is increasingly important for optimization of re-entry spacecraft design and the development of advanced aerospace technologies. For kinetic simulation methods, it is convention to enforce ions and electrons to diffuse at the same rate, known as the ambipolar diffusion approximation. This approach circumvents costly resolution of fast electron motion, but neglects the complex plasma dynamics of ions and electrons. Almost all studies that investigated the efficacy of the ambipolar diffusion approximation in hypersonics report noticeable differences in flowfield properties when electrostatic modeling is used, including increases in vehicle surface heat flux and decreases in electron temperature. However, it is unknown whether these reported differences originate directly from acceleration and deceleration of charged species through the electric fields and momentum-exchange collisions between charged and neutral species, defined as first-order effects, or from subsequent interactions with particles experiencing first-order effects, defined as second-order effects. Kinetic hypersonic flow simulations with electrostatic modeling are performed with argon to quantify the validity of the ambipolar diffusion approximation in terms of capturing first-order plasma effects along a one-dimensional stagnation streamline. Three different plasma diffusion regimes are studied under two sets of rarefied freestream flow conditions. The approximation is evaluated in terms of predicting plasma density distributions, electron temperature, and stagnation point heat flux. New criteria are proposed for identification of plasma diffusion regimes in hypersonic flows and use of the ambipolar diffusion approximation.
Jacob Emil Mencke, Thomas Stucker, Paolo Ricci
Boundary conditions for a drift-kinetic model at the collisional presheath entrance with perpendicular incidence of the magnetic field to the wall are derived and numerically implemented. The drift-kinetic model for the plasma is based on the expansion of the ion distribution function on a Hermite-Laguerre basis, and the evolution of the resulting gyromoments. A linear-plasma-device geometry is considered. Comparison with simpler simulations with previously used ad hoc boundary conditions is presented. For the new set of boundary conditions, a significant increase of the plasma outflow to the wall is observed, leading to a significantly smaller plasma density in the whole volume of the device.
D. Tsiklauri
We establish a self-consistent 2D hydrothermodynamic analytical model for the localized thermal ablation of dense human tumors using high-intensity focused ultrasound. By expanding compressible Navier-Stokes equations up to second order, we demonstrate that within a structurally stationary cellular tumor matrix, acoustic streaming (acoustic wind) velocity is suppressed. This constraint forces the absorbed wave momentum flux to transfer entirely into localized, time-averaged, static, second order, pressure gradients, converting the bulk acoustic energy directly into localized heat. Using a short, 1 s, duration, high-amplitude top-hat pulse, we solve the simplified Pennes bioheat transfer equation within non-diffusive timescales. Adapting the hydrodynamic optimization framework established by Tsiklauri (2026), we derive a natural physical criterion where the acoustic absorption coefficient matches half the inverse target depth, α=1/(2x0), proving that the optimal operational frequency scales inversely with transmission distance. We show that while incident plane waves overheat upstream tissues due to exponential decay, a spherically focusing wave geometry effectively bypasses healthy tissue boundaries via geometric convergence (∝1/r2). Analytically solving the non-isothermal Arrhenius injury integral yields a sharp lesion boundary radius at rb=0.75w0. Volumetric averaging bounded strictly within this necrosis perimeter demonstrates that the average tumor temperature reaches 72.1∘C while central point values peak at 90∘C. Finally, convolving the post-pulse thermal profile with a 2D free-space Green's function verifies immediate, monotonic temperature decay below 60∘C at the boundary, demonstrating complete structural containment and explaining the >90% localization rates observed in clinical applications.
Luca Barbieri, Pascal Démoulin, Daniel Verscharen
We investigate stationary states of a collisionless, gravitationally stratified plasma atmosphere composed of electrons, protons, and alpha particles by extending Pannekoek--Rosseland theory to multispecies and multi-temperature plasmas. Starting from Liouville's theorem, we derive the self-consistent ambipolar electric field from kinetic equilibrium and charge neutrality. For a single-temperature atmosphere, we obtain analytical expressions for the ambipolar field, show its dependence on alpha-particle abundance, and determine the relative stratification of the three species. A first-order analytical approximation to the electrostatic potential accurately reproduces the numerical solution. We then generalize the formalism to multi-temperature plasmas generated by stochastic boundary heating, representing the stationary distribution as a superposition of Maxwellian populations. Gravitational filtering produces non-exponential density profiles and increasing temperatures with altitude, while preserving the relative species stratification, with alpha particles most strongly stratified and protons least. The ambipolar electric field contains a dominant gravitational contribution, corresponding to the generalized Pannekoek--Rosseland field, and a thermoelectric contribution arising from species-dependent temperature gradients, which accounts for its non-monotonic structure. These results provide a framework for studying the combined effects of plasma composition and stochastic heating in gravitationally stratified astrophysical plasmas.
S. Hilsabeck, S. Dannhoff, C. A. Walsh +3
Experiments at the OMEGA EP laser facility were designed and executed to study plasma expansion into hohlraum-relevant gas fills (0.3-0.6 mg/cc of helium), providing a surrogate platform for investigating hohlraum wall blow-off, non-local transport, and magnetized plasma effects. We observe well-defined density features and filamentary structures as laser-driven copper plasma expands into a low-Z background gas. Shadowgraphy resolves sharp density features over time and reveals fine-scale filamentation in the laser spot region with characteristic transverse scales of 10-100 microns near the foil surface. Proton radiography provides sensitivity to path-integrated magnetic fields and density modulations throughout the bubble volume. We extract the bubble expansion as a function of time for two gas pressures, 350 psi (producing 0.3 mg/cc equivalent conditions) and 700 psi (0.6 mg/cc equivalent conditions), and compare the measured propagation to magnetohydrodynamic simulations performed with Gorgon and HYDRA. While the large-scale shape of the bubble is well reproduced by both codes, the time-dependent expansion rate shows significant discrepancies (20-50% faster) compared to experimental observations between 1 and 3 ns. This leads to increasingly larger differences in bubble sizes at later times. The optical measurements of bubble expansion and evolution of small-scale structures point to additional constraints required for Biermann-battery field generation, thermal transport, and instability growth in hohlraum-relevant plasmas, to ensure accurate, predictive modeling of gas-filled hohlraums.
Vasily Kozhevnikov, Andrey Kozyrev, Elena Klepalova +2
This work introduces a physics-informed neural network (PINN) framework for reconstructing electron energy spectra from sparsely sampled attenuation-curve data. Leveraging the NVIDIA PhysicsNeMo platform, the proposed mesh-free methodology operates directly on raw experimental datasets while explicitly incorporating all experimental uncertainties. Validation on subnanosecond electron beam measurements demonstrates that the approach accurately resolves complex, multi-peaked spectral features of energy distribution. The framework enforces physical consistency through embedded governing principles and exhibits substantial predictive capability for energy spectrum reconstruction from noisy, low-precision, and sparse experimental data.
Yashika Ghai, Donald A. Spong, Jacobo Varela +1
Fast and accurate prediction of energetic-particle transport driven by Alfvén eigenmode (AE) instabilities is essential for integrated modeling workflows used in the design and optimization of burning plasma fusion reactors. In this work, we develop machine-learning-based surrogate models for rapid prediction of energetic beam and alpha-particle transport fluxes, together with predictive uncertainty estimates, for an ITER steady-state scenario. Two complementary surrogate methodologies, Gaussian process (GP) regression and hierarchical neural networks (NNs), are trained using nonlinear FAR3d gyrofluid simulations of energetic-particle transport. A flux-variability analysis demonstrates that the selected plasma-state representation provides a sufficiently unique parameterization of the nonlinear transport response over most of the sampled feature space, thereby justifying the surrogate formulation. Both surrogate models reproduce the nonlinear transport fluxes with high predictive accuracy while reducing the computational cost of transport evaluation by approximately five to six orders of magnitude relative to direct nonlinear FAR3d simulations. Although the two approaches achieve comparable predictive accuracy, they exhibit distinct uncertainty characteristics: the GP provides more consistent global uncertainty estimates, whereas the NN more clearly distinguishes between different transport regimes. This work establishes a proof of concept for developing machine-learning surrogate models of energetic-particle transport that are sufficiently accurate and computationally efficient to be incorporated into future integrated modeling workflows.
W. Zhang, T. Grismayer, L. O. Silva
We show that the beam and field dynamics in high-energy electron-positron (e−e+) collisions are characterized by a new dimensionless parameter introduced as ε in this study. The disruption effect deflects the particles transversely at angles equal to ε. The particles simultaneously undergo deceleration of longitudinal velocities (a ``braking effect"). The deceleration scales as ∝ε2. A longitudinal electric field is further provoked, whose amplitude scales as ∝ε. We identify ε≳1 (with large-angle disruptions) as a novel extreme regime, where the transverse motion becomes strongly relativistic. The braking effect completely stops and further reverses the beam propagation. Our theoretical model is in excellent agreement with electromagnetic particle-in-cell simulations. The previous beam-beam studies, including legacy numerical codes, apply only to the ε≪1 regime. They fail to capture the correct beam features and collision luminosities, and overestimate beam-beam effects (including beamstrahlung and pair production) for considerable ε, thus demonstrating the need for fully electromagnetic particle-in-cell codes to study these regimes.
Radhika T. P., Satyananda Kar
This study investigates the effect of gas flow rate on the gas temperature and discharge characteristics of a reinforced radio frequency cross-field atmospheric pressure plasma jet (APPJ) with an additional floating electrode. The plasma jet length, electron excitation temperature, electron density, and reactivity were enhanced by introducing copper floating electrodes of varying widths. However, this enhancement was accompanied by an undesired rise in gas temperature, limiting the plasma's application for heat- sensitive materials. To control this temperature rise, the gas flow rate varied from 1.5 to 9 lpm, showing a significant reduction in gas temperature from 438 K to 402 K as the flow rate increased, particularly at higher input powers. The study reveals that while an increase in gas flow rate initially improves ionization and reactivity by increasing electron excitation temperature and density, the insufficient input power for ionization at higher flow rates causes a decline in these parameters due to reduced ionization efficiency. Further optimization was achieved by increasing input power, which allowed better utilization of neutral atoms and improved plasma reactivity even at higher flow rates. The findings highlight the importance of tuning both gas flow rate and input power to maintain optimal plasma performance for various applications, particularly where controlled gas temperature and high reactivity are essential.
Tejashwi Rana, Aishik Basu Mallick, Radhika T P +3
The enhancement of living standards has significantly contributed to the rapid growth of urban populations, resulting in a substantial increase in municipal solid waste (MSW) generation. This trend underscores the critical need for sustainable, environmentally friendly, cost-effective, and highly efficient waste management solutions. This study highlights the pressing necessity for effective MSW management and examines plasma pyrolysis/gasification as an emerging technology to address this challenge. The article provides a detailed analysis of thermal plasma generation techniques employing diverse power sources, including direct current, alternating current, radiofrequency inductively coupled, and microwave-based systems. A comparative evaluation of various plasma torch designs is conducted, emphasizing their applicability in waste-to-energy and waste treatment processes. A comprehensive overview of the treatment of a broad spectrum of waste materials, such as MSW, sewage sludge, coal, wood, plastics, tyres, and rubber, using thermal arc plasma technology is presented. The process predominantly converts waste into a combustible gas (syngas) with a calorific value ranging from 5 to 15 MJ/Nm3 and produces vitrified slag or ash as a by-product. The findings suggest that thermal plasma pyrolysis/gasification offers a promising approach to waste management, facilitating energy generation and material recovery while addressing the challenges of increasing MSW generation.
Suryasunil Rath, Satyananda Kar
Over the past decade, atmospheric pressure discharges in the microwave frequency range have gained significant attention due to their promising applications in material processing, CO2 dissociation, waste management, hydrogen production, water treatment, and more. This study presents the development and characterization of a waveguide-based microwave atmospheric pressure plasma jet (MW-APPJs), focusing on its design, diagnostics, and operational parameters. The setup incorporates a microwave power source, microwave waveguide networks, including the applicator section, and diagnostic tools for measuring plasma properties. Optical emission spectroscopy (OES) is employed to analyze the reactive species and determine plasma parameters which include electron excitation temperature (Texc) and electron number density (ne). The characterization highlights the influence of spatial and temporal gradients, gas flow rates, and power input on plasma behaviour. From OES, the Texc and ne variations were against the power increment. The thermocouple variations are also plotted with power.
A. Saltzman, P. Rodriguez-Fernandez, A. Ho +8
Impurity composition, plasma shape, and pedestal density all provide strong levers on fusion power. Here, we explore the ways in which their variation changes fusion power and seek to find the optimum of these parameters. The key impacts of these variables are through changes in the core turbulent transport, the density of the fuel species, the pedestal pressure, and the plasma volume. ITG stabilization due to increased amounts of impurities is observed. The dependence of all of these parameters on the pedestal pressure is especially complicated because of the separate impacts on the peeling and ballooning modes, which can each limit the pedestal. Optimization of this multidimensional operating space is enabled by the use of Bayesian optimization, resulting in an operating point similar to ARC V3A with ~30% more fusion power and a higher fusion power density. Increased shaping parameters, including elongation, triangularity, and squareness are all beneficial, as is high Zeff. When elongation is also allowed to vary, a ~65% increase in fusion power can be achieved. While not commonly considered, we find squareness is an important lever on fusion power. The plasma performance is limited by the Greenwald density limit constraint. This workflow developed here and demonstrated with the example of ARC V3A can readily be applied to other tokamak designs.