Particle Flux Research Articles

Optimizing 211At production cross section by studying the rise of 210At cross section: First measurement using Linac SPIRAL2.

A bstract We entertain the possibility that transient astrophysical sources can produce a flux of dark particles that induce ultra-high-energy signatures at neutrino telescopes such as IceCube and KM3NeT. We construct scenarios where such “dark flux” can produce meta-stable dark particles inside the Earth that subsequently decay to muons, inducing through-going tracks in large-volume neutrino detectors. We consider such a scenario in light of the 𝒪(70) PeV ultra-high-energy muon observed by KM3NeT and argue that because of its location in the sky and the strong geometrical dependence of the signal, such events would not necessarily have been observed by IceCube. Our model relies on the upscattering of a new particle X onto new metastable particles that decay to dimuons with decay lengths of 𝒪(100) km. This scenario can explain the observation by KM3NeT without being in conflict with the IceCube data.

The given article describes the improved model for analytical computation of the probability of Earth’s satellite collision with particles of meteor streams. An original statistical approach is proposed. Depending on the mass of the meteoroid, its velocity, angle of attack, and the physical characteristics of the impactor (space particle) and the target (satellite), the degree of potential damage to the spacecraft, such as depressurization or erosion of its casing, especially solar panels, is determined. To describe the formation of an explosive crater due to a collision, the Öpic theory of meteor crater formation was used, which has been repeatedly tested and has given good results. The theoretically calculated depth of the crater on the surface of the spacecraft was chosen as the criterion for the degree of damage, and damage was considered to be encounters with particles that leave craters 0.2 cm deep, which at a normal angle of attack and a speed of 30 km/s, with an iron casing of the satellite, gives a diameter of a stone meteoroid of 0.19 cm and a mass of 0.013 g. The masses of particles that lead to erosion of the casing are several orders of magnitude smaller. To plot the influx of sporadic meteors to Earth (or the flux of particles in orbit), a cumulative distribution was chosen, defined for the mass range from 0.000001 to 100 g. This distribution was used to calculate the influx from meteor shower particles through the zenith hourly rates of the streams and the sporadic background. For certainty, the most powerful meteor showers were taken into account — eight in total: Lyrids, h-Aquariids, Southern d-Aquariids, Perseids, Orionids, Leonids, Geminids, and Quadrantids. Additionally, the model calculated the time of screening a satellite in a given orbit from stream meteoroids by a planet and its atmosphere. To calculate the effective surface area of a satellite for the direction of the meteor stream, an analytical model of the satellite composition from three-dimensional geometric primitives is proposed. Unfortunate- ly, its use is limited when there is a significant degree of screenization of one geometric primitive by another; in this case, it is proposed to use a numerical approach. As an example, an estimate of the probability of damage to a hypothetical spacecraft with a maximum effective area of about 8 square meters over the course of a year is given. It was 0.00002 for meteor showers, which is about four times less than the impact of the sporadic meteor background.

Abstract The paper develops a new statistical method for forecasting the arrival time and maximum flux of solar energetic particle (SEP) events. We recently showed the persistent behavior of the SEP time series during SEP events. In that study, we also used persistence to determine the onset time (OT) of an SEP event and suggested using the entropy change in a time domain called natural time under time reversal ΔS as a way to estimate the maximum SEP flux of the ongoing SEP event. Here, we use EPI-Lo data for H+ below 2 MeV over the whole Orbit 15 from the Integrated Science Investigation of the Sun (IS⊙IS) instrument suite on board NASA’s Parker Solar Probe to investigate the broader applicability of these methods. We clearly demonstrate that during SEP events the corresponding time series is persistent and are able to employ the persistence-based OT method to predict SEP events. We find a prediction rate greater than 87.5% (14 out of the 16 SEP events) and a false alarm rate below 2.2%. These values when inserted in the receiver operating characteristics plane indicate that this method is highly statistically significant. Finally, we develop a relationship between the maximum SEP flux and the minimum of ΔS, allowing us to provide a prediction of the future maximum SEP flux during an ongoing event.

Marine heatwave (MHW) impacts on ecosystem functions and services remain poorly constrained due to limited time-resolved datasets integrating physical, chemical, and biological parameters at relevant scales. Here we show that combining over a decade of autonomous Biogeochemical (BGC)-Argo float measurements with water-column plankton community profiles reveals the impacts of MHWs on particulate organic carbon (POC) production, transformation, and transport in the northeastern subarctic Pacific Ocean. POC concentrations are exceptionally high during the 2015 and 2019 MHWs, linked to detritus enrichment and shifts in plankton community structure. Instead of being rapidly exported to depth, particles <100 µm accumulate in mesopelagic waters, where slow remineralization over the year reduces deep particle flux and carbon sequestration potential. This enhancement is absent in the 2014 and 2020 MHWs, underscoring variability in ecosystem responses to extreme events. These findings highlight the need for sustained, multi-platform observations to assess and predict carbon-cycle responses to thermal extremes.

Abstract An understanding of the occurrence of opacity is important for modelling the power exhaust of magnetic confinement fusion plasmas. The absorption and reemission of radiation alters the magnitude and distribution of radiation within the divertor of the fusion machines, the plasma volume within the divertor controlling and limiting the power and particle fluxes to the plasma facing surfaces. High levels of opacity can also result in changes to the ionization balance within the plasma. An analysis of a discrepancy between He II (He+) line intensity measurements observed on the JET machine and the collisional-radiative models describing them has resulted in a better understanding of the behaviour of the radiation from He II. This has led to a simple technique for monitoring opacity within the He II ionization stage. The technique has enabled three periods of He operations to be surveyed in order to determine the occurrence and severity of opacity in He discharges. A precise calculation of opacity is difficult, although estimates of escape factors and optical depths are possible for all pulses in which opacity is judged to be significant. These estimates do not fit the available line-of-sight opacity models and allow an alternative model that more closely matches the experimental results to be derived. The sensitivity of this model to its various components is discussed.

Among the few ways that allow or could allow us to probe the early Universe from the observation of a flux of primordial particles, there is one possibility which has been little studied: the observation today of high energy neutrinos which could have been emitted shortly after the Big Bang, from the decay or annihilation of early universe relics. We perform a general study of such a possibility. To this end, we first emphasise that these neutrinos could display various kinds of sharp spectral features, resulting from the primary energy spectrum at emission, and from how this spectrum is smoothed by redshift and radiative correction effects. Next, we determine the ranges of mass (from a fraction of eV all the way to the Planck scale) and lifetime of the source particles along which we do not/we do expect that the sharp spectral feature will be altered by interactions of the neutrinos on their way to the detector, mainly with the cosmic neutrino background or between themselves. We also study the theoretical (i.e. mainly BBN and CMB) and observational constraints which hold on such a possibility. This allows us to delineate the regions of parameter space (mass, lifetime and abundance) that are already excluded, hopeless for future observation or, instead, which could lead to the observation of such neutrinos in the near future.

Abstract. Meteorological processes such as gust fronts, roll structures, internal boundary-layer development and smaller-scale turbulence complicate the physical interpretation of measured aerosol particle properties, fluxes, and transport in the marine atmospheric boundary layer (MABL). To better decipher maritime aerosol measurements by aircraft, ships, and towers we describe an ensemble of particle trajectories using high-resolution large eddy simulations (LES) of surface-emitted aerosol particle within a Lagrangian framework. We identified two clusters of particle trajectory types from which we created probabilistic distributions of particle histories: (a) short-lived particles that do not exit the surface layer and are subsequently deposited back to the ocean; and (b) much older particles that are able to exit the surface layer into the mixed layer and subsequently oscillate up and down through convective roll structures. After emission in a neutral atmosphere, particles slowly disperse through the MABL requiring, on average, up to 100 min to mix to the ∼ 570 m deep mixed-layer inversion. However, for even slightly unstable conditions, particles are rapidly transported to the top of the MABL in roll structure updrafts, where they then more slowly diffuse downwards, with some similarities to a looping plume rise to the stable inversion followed by fumigation. Consequently, particles can exhibit a bimodal lifetime distribution that results in different particle ages by altitude. Further, based on wind speed and stability, the initial looping behavior following an emission event spans 15 to 30 min and may result in sampling “blind spots” up to 15 km downwind. Overall, our findings suggest that there should be a consideration of the representativeness of particle ages, even in what is often assumed to be a well-mixed MABL. This representativeness is related to how long particles have been suspended and whether they were sourced locally, which is critical for situations such as for measuring wind-generated emissions or ship track plumes. Further, the Lagrangian technique for treating the particle transport captures the inherently random motion of the MABL turbulence and does not exhibit artificial numerical diffusion. As such, it produces differences when compared to a traditional, column-based eddy-diffusivity approach used in mesoscale to global scale models. We used the LES to drive a one-dimensional (1D) column model to approximate single grid point physics. The results were starkly different near the surface, with the 1D column model missing the looping behavior and showing a slow upward dispersion. This difference in the 1D and LES frameworks is an excellent example of subgrid problems and may explain some of the differences between observations and global and mesoscale model simulations of marine particle vertical distribution and dry scavenging.

The effect of magnetic shear on ballooning-driven plasma edge turbulence is studied through nonlinear simulations complemented by linear numerical and analytical investigations. Nonlinear, 3D, global, flux-driven simulations using the GBS code show that the scale separation between radial, x, and poloidal, y, size of turbulent eddies, kx≪ky, considered by Ricci et al. [“High- and low-confinement modes in simple magnetized toroidal plasmas,” Phys. Rev. Lett. 100, 225002 (2008)] and extensively used to predict pressure gradient lengths, scrape-off layer width, particle and heat fluxes, is observed with high magnetic shear. In contrast, for low magnetic shear, kx∼ky is observed, with fluctuation properties resembling those shown by recent low-shear stellarator simulations reported in Coehlo et al. [“Global fluid simulation of plasma turbulence in stellarators with the GBS code,” Nucl. Fusion 64, 076057 (2024)]. Global linear investigations of the ballooning mode qualitatively capture the transition in mode structure with varying magnetic shear, showing that kx≪ky is achieved with sufficiently strong poloidal mode coupling enhanced by increasing magnetic shear, resistivity, toroidal mode number, and equilibrium gradient scale length. This is confirmed by an analytical study considering a dominant poloidal mode and its sidebands, which highlights that the poloidal mode structure is determined by curvature and k∥ effects.

Abstract A new method for determining the particle flux density in the beam of a neutral beam injector (NBI) for magnetically confined fusion plasmas is presented. The method uses a force probe to measure the momentum transfer from beam particles to a small target and has been applied at the BATMAN experimental facility at the MPI Garching. The experiments presented in this report are performed in the non-neutralized negative ion beam. It is found that the force measured at a distance of 1.4 m from the negative ion source correlates well with the momentum flux that is calculated from the ion energy and the averaged extracted ion current density. Graphical abstract Schematic of the force-probe diagnostic for momentum-flux measurements in the negative hydrogenion beam at the BATMAN facility. A water-cooled shield with a 5 mm aperture limits the beam spot on an L-shaped tungsten target mounted on an interferometric cantilever probe, enabling charge-independent local flux determination 1.4m downstream of the source

Abstract An accurate understanding of the Earth's ring current dynamics is integral to predicting the impacts of geomagnetic storms. We use physics‐based models to simulate the ring current such as the Ring‐current Atmosphere interactions Model with Self‐Consistent Magnetic Field (RAM‐SCB). However, physics‐based models are computationally expensive. Therefore, we employ reduced order models (ROMs) to speed up computation. In this study, we present a ROM of RAM‐SCB using autoencoder neural networks (AE) as well as orthogonal autoencoders (OAE) and compare it to a previous study which used Principal Component Analysis (PCA). We also use this ROM to produce a Reduced Order Probabilistic Emulator (ROPE), where we use an ensemble Long Short‐Term Memory (LSTM) in combination with ResNets (LSTM + ResNet) neural networks to emulate RAM‐SCB in the reduced state. We show a significant improvement in using AEs over PCA and present a ROPE that can forecast the ring current particle fluxes 1 hour ahead.

Turbulent transport is a decisive factor in determining the pedestal structure of H-modes. Here, we present the first comprehensive characterization of gyrokinetic turbulent transport in a JET hybrid H-mode pedestal. Local, linear simulations are performed to identify instabilities and global, nonlinear electromagnetic simulations reveal the turbulent heat and particle flux structure of the pedestal. Our analysis focuses on the Deuterium reference discharge #97781 performed in the scenario development for the Deuterium–Tritium campaign. We find the pedestal top transport to be dominated by ion temperature gradient (ITG) modes. In the pedestal center turbulent ion transport is suppressed and electron transport is driven by multi-faceted electron temperature gradient (ETG) modes, which extend down to ion-gyroradius scales. E×B shear is observed to strongly reduce the absolute turbulence level in global, nonlinear simulations. Furthermore, impurities are shown to reduce the main ion transport. Dedicated density and ion temperature profile variations test the sensitivity of the results and do not find strong differences in the turbulent transport in more reactor-like conditions.

Context. Interplanetary (IP) shock waves offer an unparalleled opportunity to directly study the elusive mechanisms of particle acceleration that are pervasive in our Universe. Novel spacecraft missions, orbiting poorly-explored regions of the heliosphere, opened a new observational window on particle acceleration at IP shocks that is relevant to space and astrophysical plasmas. Aims. We address shock variability and its effects on the production of accelerated particles at different energies. We leveraged three different missions that directly observed a strong IP shock in a range of separations that cannot be achieved with a single mission. We linked spatial shock irregularities and evolutionary effects to the observed energetic particle responses in the shock passage at the three different heliospheric vantage points. Methods. We exploited direct observations of magnetic field, plasma, and energetic particle fluxes from the Wind and ACE missions at 1 AU and from the Solar Orbiter spacecraft. They are well-aligned radially at 0.8 AU. We devised a new technique based on the cross-correlation of energetic particle profiles to quantitatively address the variability in the characteristics of energetic particles at different points in space and time. Results. We show that ions with different energies respond differently to the shock passage in the range of observer separations 0.02−0.2 AU we explored. The shape and behavior of high-energy (⪆0.5 MeV) particle profiles vary between the 0.8 and 1 AU observations, and we suggest that this is caused by shock-evolution, in which high-energy particles are produced less efficiently at 1 AU than at 0.8. Finally, we show that shock and ambient spatial irregularities that are observed throughout the event modulate the energetic particle responses at different energies.

Ultraheavy dark matter candidates evade traditional direct detection experiments due to their low particle flux. We explore the potential of large underwater acoustic arrays, originally developed for ultrahigh energy neutrino detection, to detect ultraheavy dark matter interactions. These particles deposit energy via nuclear scattering while traversing seawater, generating thermoacoustic waves detectable by hydrophones. We present the first robust first-principles calculation of dark matter-induced acoustic waves, establishing a theoretical framework for signal modeling and sensitivity estimates. Our framework incorporates frequency-dependent attenuation effects, including viscous and chemical relaxation, not considered in previous calculations. A sensitivity analysis for a hypothetical 100 km3 hydrophone array in the Mediterranean Sea demonstrates that such an array could extend sensitivity to the previously unexplored mass range of 0.1−10 μg (∼1020–1023 GeV), with sensitivity to both spin-independent and spin-dependent interactions. Our results establish acoustic detection as a complementary dark matter search method, enabling searches in existing hydrophone data and informing future detector designs.

Abstract The improved performance of the long-legged alternative divertor configurations on MAST-U, combining strong baffling and total flux expansion, results in stronger power and momentum losses. These lead to lower electron temperatures and peak particle fluxes at the target compared to conventional divertor configurations. The evolution of the divertor electron density profile in the detached region is characterized by a density peak building up near the target, downstream of the detachment front, with increasing upstream density, which then moves upstream from the target as the target temperature decreases (Te &lt; 0.3 eV). This behaviour is in agreement with simplified modeling based on the competition of different ion recombination processes and neutral drag acting on the plasma flow. Comparisons against SOLPS simulations generally show good agreement in the magnitude of the electron density profiles, both along and across the separatrix, but with some discrepancies in the shape of the profiles in the private flux region and near the target.

Simulation study of medical isotope production by accelerator induced reactions.

Particle Fluxes and Pressure Acting on the Cathode of a Vacuum Arc in Terms of a Kinetic Model of the Cathode Spot

Sediment magnetic record of anthropogenic environmental changes in the catchment of a typical submerged macrophyte-dominated lake over the last approximately 168 years.

Organic sulfur (OS) in the ocean is produced in vast quantities by primary producers that fix inorganic sulfate into proteins, metabolites, and other ubiquitous biomolecules. As biogenic OS is transported and transformed through the marine environment, it is joined by OS from two additional sources: abiogenic OS from sulfurization under anoxic conditions, and geological OS from the weathering of sediments and rocks. Important differences in the properties of the OS from these sources affect its fate in the environment and underlie the formation of recalcitrant dissolved organic matter and sedimentary kerogen. This review builds connections between the rapid OS cycle in the surface ocean and these longer-lived reservoirs, applying our growing knowledge of particle fluxes and organic matter dynamics at the sediment-water interface. Future studies on marine OS are poised to help us better understand the implications of these fluxes for the carbon cycle and climate across human and geological timescales.

Cilia are found on the epithelia of almost all metazoans, so their absence from the epithelia of all but one class of Porifera is puzzling. Homoscleromorph sponges possess ciliated epithelia, but their function and evolutionary history within Porifera are unclear. We compared the ciliary beat frequencies (CBFs) of cilia on outer epithelia of the homoscleromorph sponge Oscarella sp. with those of other animals to suggest possible functions for the cilia. Settled Stage 4 buds, or juveniles, were found to have a higher CBF than free-moving Stage 1 buds, and CBF was within the range of cilia that function in mucus transport in other aquatic invertebrates. Scanning Electron Microscopy (SEM) images of buds fixed with ruthenium red to detect the presence of mucus showed that mucus was associated with the cilia of the exopinacoderm and both SEM and immunofluorescence images revealed fields of homogeneously oriented cilia. Confocal imaging of fluorescent beads also showed that cilia beat in the same direction. Movement of beads was reduced by nocodazole treatment indicating that the movement of particles over the surface was caused by ciliary beat. These results suggest that cilia on the epithelia of Homoscleromorph sponges are involved in mucociliary-driven particle flux, and may be used to clean the surface using mucus.