Particle Flux Research Articles

Wave-particle resonant interactions play a crucial role in the dynamics of energetic particle fluxes across various space plasma systems, including the near-Earth plasma environment. When waves are sufficiently intense, these interactions become strongly nonlinear, with effects of particle phase bunching and trapping. This paper examines several examples of nonlinear resonant interactions involving energetic electrons, intense whistler-mode waves, electromagnetic ion cyclotron waves, and kinetic Alfvén waves within the Earth's inner magnetosphere. We focus on a specific scenario when resonant interactions occur near the threshold of the nonlinear regime. We demonstrate that, for such threshold wave amplitude, the classical model of resonant wave-particle interactions, represented by the pendulum equation, can be reduced to Type I Painlevé equation. We derive an equation describing the scaling of electron momentum (and thus energy) change with wave amplitude for this regime. We discuss the importance of this scaling in explaining observed energetic electron losses in Earth's inner magnetosphere.

The climatology of the deep particle flux in the oligotrophic western North Atlantic gyre, 1978–2022

Abstract The nuclear reaction cross-sections of the 93Nb(p,n)93mMo process were measured in three experiments up to 17 MeV proton energy by using the stacked target foil technique. The target stacks were irradiated at the cyclotron JSW BC 1710 at the Forschungszentrum Jülich, INM-5. The natCu(p,x)62/63Zn reactions were used as monitor reactions to determine the proton particle flux and the incident proton energy. The experimental results were compared with literature data and with theoretical nuclear model calculations based on the TALYS-1.96 code and the data from TENDL-2023. Furthermore, it could be shown that the 93Nb(p,n)93mMo reaction delivers sufficient amounts of activity for the later application of 93mMo as a tracer to optimize the radiochemical separation of low specific activity 99Mo and 99mTc.

Abstract The present work is focused on a 3D numerical assessment of the Wendelstein 7-X (W7-X) particle exhaust. For all the numerical simulations the direct simulation Monte Carlo solver of the DIVGAS workflow, has been employed. The complex 3D geometry of the sub-divertor region includes the pumping gap panel, supporting structures, cooling pipes as well as the cryo-vacuum pump. All the considered flow simulations correspond to the Standard magnetic configuration of W7-X. The main conclusions, which can be extracted from the present numerical analysis could be summarized as follows; The coupling between EMC3-EIRENE and DIVGAS, which considers the fact that the incoming neutral particle flux at the sub-divertor is based on realistic plasma background, has been demonstrated. Three plasma scenarios have been considered, for which is clearly seen that by increasing the heating power, the neutral pressure as well as the resulting pumping efficiency is increased. The obtained numerical results of the neutral pressure in the sub-divertor lie within a more general scan matrix, which assumes a wider range of incoming particle flux, namely 1019–1024 (s−1). It has been observed that, the sub-divertor neutral pressure is proportional to the incoming neutral particle flux, with the effective pumping speed to be a constant of proportionality. The influence of switching off the cryo-vacuum pump on the sub-divertor pressure is rather modest and a weak increase of the neutral pressure in the sub-divertor is expected. Correlations of the sub-divertor pressure with the total incoming particle flux as well as the individual pumped flux at each of the AEH and AEP sections have been deduced. Moreover, it has been demonstrated that the influence of the incoming neutral particle flux on the albedo coefficient at the AEH and AEP pumping gaps is rather weak. All the above numerical findings will actively support the optimization of the W7-X particle exhaust, in view of future experimental campaigns.

We study the relaxation process of two driven colloidal suspensions in contact, to a joint steady state, similar to the process of thermalization. First, we study a single suspension, subjecting it to random driving forces via holographic optical tweezers, which agitate it to a higher effective temperature. Interestingly, the effective temperature of the suspension, defined by the Einstein relation, exhibits a nonmonotonic dependence on the driving frequency. Next, we follow the flux of particles between two such suspensions in diffusive contact, starting from a uniform density and relaxing to a state with zero net particle flux. At high driving frequencies, we show that the density distribution at steady state is determined by equating the ratio of the chemical potential to the effective temperature in both systems, reminiscent of the thermal equilibrium behavior.

In recent years, aluminum recycling has significantly increased, particularly in Brazil, where the recycling rate of aluminum cans exceeds 95%. Aluminum dross is generated as a byproduct during the melting and recycling processes. The composition and morphology of this dross vary according to its metallic aluminum content. This study analyzed the recovery of aluminum from secondary dross, focusing on particle size and the amount of flux salt used. The results showed that particles larger than 7.5 mm yielded an aluminum recovery rate of 73.99% with 15% salt. The melting of larger particles improved aluminum recovery, suggesting greater process efficiency when targeting particles above 3.0 mm.

Hybrid-type generators of non-equilibrium low-temperature plasmas are considered in the context of possible ways to control the plasma volume location in setup working chambers as well as plasma particle concentrations and fluxes. Planar and coaxial chambers were used in experiments with plasmas excited by the joint action of non-relativistic electron beams in combination with capacitive RF gas discharges on gases of forevacuum pressure. The electron-beam injection into the discharge was found to rearrange the plasma volume and affect both the plasma column and sheaths, resulting in the dark and bright zone replacement. When the beam scans over the plasma volume, these zones follow the beam trajectory. Electron heating, plasma-generating gas heating, and extra gas molecule excitation explain the external RF-electromagnetic field influence on the preliminarily excited electron-beam plasma within the pressure range 0.1–10 Torr. The effect turned out to be mostly pronounced at upper pressures of this range and at higher gas temperatures. Physical models describing the experimentally observed phenomena and effects were proposed and used in computer simulations within wide ranges of controllable parameters responsible for the hybrid plasma properties. Effects of plasma-generating gas pressure, gas heating, external electromagnetic field, and mass-transfer controlled by the ambipolar diffusion on plasma particle concentrations were estimated both separately and self-consistently.

Sinking particles are important conduits of organic carbon from the euphotic zone to the deep ocean, but their origin and community composition are still a matter of investigation. Events in the northwestern Sargasso Sea, such as winter convective mixing, summer stratification, and mesoscale eddies, affect the vertical and temporal composition and abundance of pelagic and particle-attached microorganisms. We sampled the euphotic zone and collected sinking particles using shallow traps near the Bermuda Atlantic Time-series Study site during the spring and summer of 2012 to assess eddy-driven impact on microbial communities. In the spring, we sampled a cyclonic eddy, while in the summer, we targeted both the center and edge of an anticyclonic eddy. Prokaryotic and photoautotrophic (plastid and cyanobacteria) communities were analyzed using V4–V5 amplicons of the 16S rRNA gene. Community and clustering analysis of prokaryotes revealed a clear separation between seawater and particles samples. However, the same was not observed for photoautotrophs. Indicator species analysis showed that small phytoplankton taxa dominated particle communities. Interestingly, differential abundance analyses revealed that the large centric diatom, Rhizosolenia, generally rare in the oligotrophic Sargasso Sea, was enriched in the photoautotrophic communities of sinking particles collected in the center of the anticyclonic eddy with unusual upwelling due to eddy–wind interactions. We hypothesize that the steady contribution of small-celled phytoplankton to particle flux is punctuated by pulses of production and flux of larger-sized phytoplankton in response to episodic eddy upwelling events and can lead to higher export of particulate organic matter during the summer.

Abstract Determining the relative contribution of solar flares versus coronal mass ejections in large solar energetic particle (SEP) events is a long-standing problem. Flare-accelerated particles may travel through complex magnetic fields in the eruption region and escape into interplanetary space, thereby contributing to large SEP events. The process by which flare accelerated particles are released into the heliosphere is poorly understood and yet is critical to advancing our understanding of SEPs. In this work, we address the release problem by solving the focused transport equation in the context of a 2.5D ARMS magnetohydrodynamic simulation of a breakout coronal mass ejection (CME)/flare event. We find that particles accelerated by flare reconnection can be released into interplanetary space through interchange reconnection between closed and open field lines. These particles can contribute directly to SEP events and may become an important seed population for further acceleration by CME-driven shocks. Additionally, we find that the energetic particle fluxes in the inner heliosphere remain elevated for an extended period, allowing them to contribute to SEP acceleration by subsequent CMEs. This study represents the first direct particle modeling of how flare-accelerated particles can contribute to major SEP events.

Proton–stainless steel interactions occurring at the first collimator of the Middle East Technical University Defocusing Beamline generate high-energy secondary particles like neutrons ( ≤ 23 MeV), gamma rays ( ≤ 14 MeV), and electrons and positrons ( ≤ 7.0 MeV) with particle fluxes between 107 to 109 particles/(cm2∙s). A neutron collimating system aiming to reduce most of these secondaries and obtain a moderate flux of fast neutrons was designed and constructed. The collimating structure consists of a moderating unit aiming to shield the outside of the system, a neutron funnel to redirect the neutrons to the desired beam geometry, and a testing station. This system funnels neutrons into a 10-cm-diameter nonuniform beam and directs them to a testing area capable of hosting up to six samples of 7.3-cm diameter and up to 3.0-cm thickness. Simulation results show neutrons with energies up to 5.0 MeV and a flux of 106 neutrons/(cm2∙s) at the testing unit, while the experimental result gives a neutron dose rate of about 22 mSv/h.

Abstract This study performs a numerical investigation into the effects of fast ions and impurities in the core region of deuterium-tritium (DT) plasma in the China Fusion Engineering Test Reactor (CFETR) hybrid scenario using the gyrokinetic code NLT. The linear simulations primarily focus on the particle fractions and the density gradients of fast ions and impurities on the linear frequencies of instabilities. The results reveal that tungsten impurities play a negligible impact on the linear frequencies of ion temperature gradient (ITG) instability and trapped electron mode (TEM), whereas argon impurities significantly suppress both ITG and TEM. Fast ions further stabilize ITG instability but destabilize TEM. Electromagnetic effects exhibit a stabilizing influence on both ITG and TEM. Nonlinear simulations demonstrate that the presence of argon impurities and fast ions significantly reduce the ion heat diffusivity, owing to the dilution effects of fast ions and argon impurities. The analysis on the poloidal spectra of perturbed electrostatic potential and DT total energy flux at the saturated stage reveal that ITG instability contributes dominantly to the turbulent transport. The DT total energy flux significantly decreases with a larger positive density gradient of fast ions/impurities. Furthermore, it is revealed that the fast ions suppress the turbulent transport through its dilution effects, while for argon impurities, in addition to the dilution effects, the density gradient effects also play a crucial role, especially under a larger positive density gradient. Moreover, as the density gradient of fast ions/impurities increases, the inward transport of deuterium and tritium particle fluxes are enhanced, and the accumulation of impurities in the core region significantly improves. 

Unlike a classical charged bosonic field, a classical charged fermion field on a static charged black hole does not exhibit superradiant scattering. We demonstrate that the quantum analogue of this classical process is however present. We construct a vacuum state for the fermion field which has no incoming particles from past null infinity, but which contains, at future null infinity, a nonthermal flux of particles. This state describes both the discharge and energy loss of the black hole, and we analyze how the interpretation of this phenomenon depends on the ambiguities inherent in defining the quantum vacuum.

We extend a recently developed dynamically self-consistent model of the Milky Way constrained by observations from the Gaia observatory to include a radially anisotropic component in the dark matter (DM) halo, which represents the debris from the accreted Gaia-Sausage-Enceladus (GSE) galaxy. In the new model, which we call a self-consistent Anisotropic Halo Model or scAHM, we derive distribution functions for DM velocity in heliocentric and geocentric reference frames. We compare them with the velocity distributions in the standard halo model (SHM) and another anisotropic model (SHM++). We compute predicted scattering rates in direct-detection experiments, for different target nuclei and DM particle masses. Seasonal dependencies of scattering rates are analyzed, revealing small but interesting variations in detection rates for different target nuclei and DM masses. Our findings show that the velocity distribution of the anisotropic GSE component significantly deviates from Gaussian, showing a modest impact on the detection rates. The peculiar kinematic signature of the radially anisotropic component would be most clearly observable by direction-sensitive detectors.

This paper explores the energy fluxes in the 6D kinetic Vlasov system. We present a novel method for calculating particle and energy flows within this framework, enabling the direct determination of energy and particle fluxes and the Poynting flux from lower moments of the distribution function, such as kinetic energy density and the momentum transfer tensor. This technique allows for identifying individual contributions of the energy flux while minimizing inherent gyro-oscillations in energy and particle fluxes. The resulting energy and particle flux expressions are compared with simulation results of ion temperature gradient turbulence, using either a local or nonlinear treatment of the temperature gradient. By computing the fluxes and the decay of the initial temperature profile from the simulation, we demonstrate good agreement with the summation of individual contributions, confirming the validity of the new method. The results indicate that energy fluxes are primarily dominated by the E×B heat flux, with additional contributions from the momentum transfer tensor and the Poynting flux. This paper also derives the residual Poynting flux in the electrostatic limit and assesses its contribution to the overall energy flux. From this analysis, we identify an additional contribution that is negligible for low-frequency gyrokinetic modes but may become significant for high-frequency modes, such as ion Bernstein waves.

Inward particle transport improves plasma confinement and facilitates the formation of transport barriers, thereby achieving advanced operating modes. However, a comprehensive understanding of the mechanisms underlying inward particle flux remains elusive. This study presents a novel machine learning approach for investigating hidden correlation between observable plasma properties and particle transport phenomena in a linear plasma device, the Peking University Plasma Test device. We developed a neural network model trained on experimental data to predict particle flux behavior under varying magnetic confinement conditions. Through SHapley Additive exPlanations analysis, we identified distinct feature importance patterns across magnetic field regimes from 530 to 1840 G. The analysis demonstrated that magnetic field dominates transport behavior in the low-field regime (530–790 G), while vorticity joined magnetic field to become the primary contributor at intermediate fields (920–1200 G). In high fields (1200–1840 G), vorticity and plasma density continued its contribution to inward particle transport. The model successfully reproduced experimental observations through plasma density modulation, validating its predictive capabilities. Our results provide new insight into the complex relationship between plasma parameters while establishing machine learning as a powerful tool for plasma physics research. This methodology offers promising applications for optimizing plasma confinement in fusion devices and understanding complex plasma transport phenomena.

Abstract The lateral transport of sediments from the shelf to the ocean interior is ubiquitous on continental margins, exerting great impacts on the characteristics and flux of sinking particles in the mesopelagic ocean. In this study, we determined the biogenic components and stable carbon isotopes in sinking particles collected from the slope of the northern South China Sea using a time series sediment trap. Laterally derived particulate organic carbon (POClateral), which originated primarily from marine sources, as indicated by the ratio of POC to particulate nitrogen ratio and POC‐δ13C, accounted for 31 ± 3% of the total POC flux during the one‐and‐a‐half‐year deployment. High fluxes of POClateral occurred in April and May 2021, comprising 69 ± 12% and 53 ± 9% of the total POC flux, respectively. This was likely due to the lateral input of shelf sediments entrained by a westward anticyclonic eddy. These allochthonous particles were mainly composed of small (<53 μm) sediments and were depleted in biogenic components, such as POC and biogenic silica (bSi). In contrast, the flux of vertically derived POC (POCvertical), that is, local biogenic POC, was strongly correlated with the surface Chl‐a concentration (R2 = 0.62, p < 0.001) and bSi flux (R2 = 0.83, p < 0.001), indicating that the POCvertical flux in the mesopelagic zone was governed by both primary productivity and the growth of diatoms, with the latter being the main controlling factor. Our results highlight that the POCvertical flux was controlled by the seasonal variations in primary productivity and the phytoplankton community structure, whereas the POClateral flux was closely linked to hydrodynamic processes, such as mesoscale eddies.

Abstract This study investigates how resonant magnetic perturbation (RMP) govern neoclassical transport and ambipolar electric field dynamics in tokamak plasmas. By integrating magnetic island geometry with collisionality dependent transport regimes, we develop theoretical models to quantify particle and heat fluxes. Numerical simulations reveal stark collisionality driven contrasts: in low-collisionality regimes (e.g., DIII-D), enhanced neoclassical transport dominates, with effective electron diffusion coefficients reaching D ~ 0.1 m2 s−1, accounting for 6.5% of the total observed electron temperature reduction at the q = 2 surface. In high-collisionality regimes (e.g., J-TEXT), neoclassical contributions are suppressed ( D ~ 10 − 4 m 2 s − 1 ), necessitating turbulence coupling to explain experimental particle losses. RMP induce collisionality dependent bifurcation of ambipolar electric fields, with reversal thresholds significantly lower in low-collisionality plasmas, consistent with DIII-D pedestal suppression observations. Crucially, we derive collisionality dependent critical RMP amplitudes for E r bifurcation, to optimize edge-localized mode suppression while minimizing transport penalties in fusion reactor.

The wastewater from Chemical Mechanical Polishing (CMP) generated in the semiconductor industry contains a significant concentration of suspended particles and necessitates rigorous treatment to meet environmental standards. Ceramic ultrafiltration membranes offer significant advantages in treating such high-solid wastewater, including a high separation efficiency, environmental friendliness, and straightforward cleaning and maintenance. However, the preparation of high-precision ceramic ultrafiltration membranes with a smaller pore size (usually <20 nm) is very complicated, requiring the repeated construction of transition layers, which not only increases the time and economic costs of manufacturing but also leads to an elevated transport resistance. In this work, halloysite nanotubes (HNTs), characterized by their high aspect ratio and lumen structure, were utilized to create a high-porosity transition layer using a spray-coating technique, onto which a γ-Al2O3 ultrafiltration selective layer was subsequently coated. Compared to the conventional α-Al2O3 transition multilayers, the HNTs-derived transition layer not only had an improved porosity but also had a reduced pore size. As such, this strategy tended to simplify the preparation process for the ceramic membranes while reducing the transport resistance. The resulting high-flux γ-Al2O3 ultrafiltration membranes were used for the high-efficiency treatment of CMP wastewater, and the fouling behaviors were investigated. As expected, the HNTs-mediated γ-Al2O3 ultrafiltration membranes exhibited excellent water flux (126 LMH) and high rejection (99.4%) of inorganic particles in different solvent systems. In addition, such membranes demonstrated good operation stability and regeneration performance, showing promise for their application in the high-efficiency treatment of CMP wastewater in the semiconductor industry.

We compare enhancements of mesospheric volume mixing ratios of hydroperoxyl radical HO2 and nitric acid HNO3, as well as ozone depletion in the Northern Hemisphere (NH) polar night regions during energetic particle precipitation (EPP) in January of 2005 and 2012. We utilize mesospheric observations of HO2, HNO3, and ozone from the Microwave Limb Sounder (MLS/Aura). During the second half of January 2005 and 2012, the GOES satellite identified strong solar proton events with virtually the same proton flux parameters. Geomagnetic disturbances in January of 2005 were stronger, with Dst decreasing up to 100 nT compared to January 2012 while the Dst drop did not exceed 70 nT. Comparison of observations made with the MLS/Aura shows the highest change of HO2 and HNO3 concentrations and also the deepest ozone destruction at the latitudinal range from 60∘ NH to 80∘ NH inside the north polar vortex right after the spike in energetic particle flux registered by GOES satellites. MLS/Aura observations show HNO3 maximum enhancements of about 1.90 ppb and 1.66 ppb around 0.5 hPa (about 55 km) in January 2005 and January 2012, respectively. The HOx increases lead to short-term ozone destruction in the mesosphere, which is seen in MLS/Aura ozone data. The maximum HO2 enhancement is about 1.05 ppb and 1.62 ppb around 0.046 hPa (about 70 km) after the onset of EPP in the second half of January 2005 and January 2012, respectively. Ozone maximum depletion is observed around 0.02 hPa (about 75 km). Ozone recovery after EPP was much faster in January 2005 than in January 2012.

Cooling of the fusion blanket first wall remains a significant challenge given the adverse conditions of heat and particle flux encountered near the plasma. Helium emerges as an attractive cooling candidate because of its chemical and neutronic inertness and separability from hydrogenic species (e.g. tritium). Because of the low thermal mass of helium, optimization of these coolant channels is warranted to provide high heat transfer performance at low pumping costs. Increasingly, computational fluid dynamics (CFD) simulations are employed to model and optimize these flow channels, and accompanying experimental data are needed to validate the predictions of these models. To provide the aforementioned experimental data, a high-pressure helium flow visualization upgrade has been designed for the Helium Flow Loop Experiment facility. This apparatus was built to American Society of Mechanical Engineers boiler and pressure vessel standards to withstand operating pressure of 4 MPa and mated to high-pressure glass windows. Seedless flow visualization is performed via high-speed background oriented schlieren (BOS), with image correlation used for time-resolved two-dimensional velocimetry at frequencies in excess of 60 kHz. Rectangular flow channel test articles are additively manufactured via laser powder bed fusion and installed into this visualization apparatus, with one-sided heating supplied by resistive heaters. The chosen test geometries were informed by prior CFD simulations, and the helium flow structures observed via BOS (detachment, recirculation, etc.) will be used for the validation of these accompanying models, in support of the design and optimization of blanket cooling channel configurations.