Particle Flux Research Articles (Page 6)

In particle radiotherapy practice it is valuable to examine, accurately measure and monitor the secondary radiation fields produced during treatment. Measurements performed non-invasively and out-of-field avoid interfering with and modifying the delivered dose treatment. Use of a simplified and compact device is advantageous for reduced cost and effort of deployment and operation. For this purpose, we examine in detail the scattered beam particles and secondary radiation field produced well beyond even meters away from the irradiated area in proton therapy. We use the semiconductor pixel detector Timepix3 implemented as a miniaturized radiation camera which we mounted at the ceiling of the treatment room. The pixel detector provides high-resolution per-pixel spectrometry with time, position, directional and tracking response. Applying radiation imaging and particle tracking techniques together with extensive experimental calibrations in well-defined radiation fields, the single detector provides the composition and spectral-tracking characterization of the complex fields. In particular, the scattered proton field at the detector position is evaluated and unfolded into spectral-directional groups which serve to map and examine the characteristics and directional origin of the radiation out of field. Detailed particle fluxes and dose rates, total and partial, are measured out of field with sub-second time resolution. Deposited energy distributions in the detector sensor are derived in wide range. Verification and complementary information are provided by numerical Monte-Carlo (MC) simulations. The combined results and presented technique can be potentially used to inspect and systematically evaluate quality assurance irradiations and treatment plans.

Abstract An important role in the cycling of marine trace elements is scavenging, their adsorption and removal from the water column by sinking particles. Boundary scavenging occurs when areas of strong particle flux drive preferential removal of the trace metals at locations of enhanced scavenging. Due to its uniform production and quick burial via scavenging, 230Th is used to assess sedimentary mass fluxes; however, these calculations are potentially biased near regions where net lateral transport of dissolved 230Th violates the assumption that the flux of particulate 230Th to the seabed equals its rate of production in the water column. Here, we present a water column transect of dissolved 230Th along 152° W between Alaska and Tahiti (GEOTRACES GP15), where we examine 230Th profiles across multiple biogeochemical provinces and, novelly, the lateral transport of 230Th to distal East Pacific Rise hydrothermal plumes. We observed a strong relationship between the slope of dissolved 230Th concentration‐depth profiles and suspended particle matter inventory in the upper‐mid water column, reinforcing the view that biogenic particle mass flux sets the background 230Th distribution in open ocean settings. We find that, instead of the region of enhanced particle flux around the equator, hydrothermal plumes act as a regional boundary sink of 230Th. At 152° W, we found that the flux‐to‐production ratio, and thereby error in 230Th‐normalized sediment flux, is between 0.80 and 1.50 for hydrothermal water, but the error is likely larger approaching the East Pacific Rise.

Abstract We present a comprehensive study of the multiple electrostatic and electromagnetic electron temperature gradient (ETG) modes with a significant upgrading of the gyrokinetic code HD7. Specifically, the non-adiabaticity of all particle species and the electromagnetic effects are taken into account in the upgraded version. Multiple electrostatic ETG (ES-ETG) modes with conventional and unconventional ballooning mode structures are found to be excited by large temperature gradients. The unconventional modes with mode-index l >0 (where l represents peak number as well as parity in ballooning space) have comparable growth rates with the conventional mode under the specific condition, e.g. 6 < R / L T e < 25 , indicating that unconventional modes are significant in L-mode or pedestal top of H-mode. In addition, different from the phenomenon of ES-ETG, multiple electromagnetic ETG (EM-ETG) modes can be excited with k ϑ ρ s > 1 and the transition of the dominant eigenstate is observed. The l = 1 EM-ETG mode has an excited threshold of β e = 0.006 (the ratio of electron pressure over magnetic pressure), indicating that the electromagnetic effect plays a key role in high β (the ratio of thermal pressure to magnetic pressure) condition. Similar to the typical ES-ETG mode, the novel EM-ETG mode is destabilized by large R / L T e and suppressed by sufficiently large (either positive or negative) magnetic shear. Talking about the transport capability, the simulation result reveals that EM-ETG mode induced particle flux is quite low ( Γ ES − ETG ≪ Γ EM − ETG ≪ Γ ITG ) while the energy flux is non-negligible compared to that induced by ion temperature gradient driven mode. Possible relevance of the results with the transport physics in transport barriers is discussed.

Atmospheric pressure plasma jets have been studied extensively in recent years because of their wide range of applications in biomedicine, surface treatments, and material processing. In this work, a two-dimensional simulation study is carried out to compare the axisymmetric discharge device configuration on the fundamental characteristics of an atmospheric pressure plasma jet and delivery dose of charged particle fluxes to the substrate surface. The plasma jets are ignited by inserting a high-voltage needle electrode inside a quartz tube containing a grounded ring electrode (single dielectric material device) or by inserting the high-voltage needle electrode inside a one-end closed quartz tube, which is inside a quartz tube containing a grounded electrode (double dielectric material device). Simulation results of the electron density and electric field show that the single dielectric material device induces a stronger discharge than that of the double dielectric material device with significantly faster propagation of plasma bullet toward to the dielectric substrate. These characteristics of the plasma jet generated by the single dielectric material electrode are accompanied with a higher dose of charged particles delivered to the substrate surface. Shielding of the high-voltage needle electrode in the double dielectric material electrode device can reduce the potential, which, in return, reduces the electric field in the jet channel, and, thus, both the jet velocity and charged particle fluxes to the substrate surface are reduced. In addition, the reduction in the distance between the high-voltage needle electrode and the grounded ring electrode in the double dielectric material device has both double-side effects on the fluxes of the charged particles transported to the substrate surface.

Exposure to Galactic Cosmic Rays (GCR) presents significant health risks to astronauts during long-duration deep space missions. Although existing studies have examined dose and particle energy spectra under GCR exposure scenarios, there is still a lack of studies covering various shielding quantities, especially regarding the self-shielding transmission characteristics of the human body. In this study, we used Monte Carlo simulations with the PHITS codes, coupled with the ICRP male reference phantom, to evaluate the performance of shielding materials against GCR. We comprehensively analyzed several physical quantities, including organ dose equivalent, absorbed dose, effective dose equivalent, and the flux and dose of secondary particles. Our findings analyzed the body's self-shielding effect and proton dose buildup effect. This study provides systematic data that offers valuable insights into astronaut safety during deep space exploration.

Autumnal settling particle fluxes were studied in the Antarctic coastal zone. The study revealed that the particulate organic carbon (POC) flux exported from the euphotic zone towards the seabed equals the magnitude of the summer pulse when typically, > 95% of the Antarctic annual flux develops. The pelagic POC flux was accompanied with centric and pennate diatoms and euphausiid faecal pellets, which together comprised most of the biogenic particles (and biogenic silica) collected in the sediment trap used in the Gerlache Strait. Our results strongly suggest that the most important drivers of the unusual seasonal extension observed for the settling particle export were increasing glacier melting and an extended productive period. The present study may provide a baseline for Antarctic coastal biogenic particle flux studies and shows that ongoing environmental warming makes the autumnal biogenic settling particle production near shore more intense than typically observed off shore.

Abstract Deuterium (D) and beryllium (Be) fluxes are obtained in JET Low-confinement mode (L-mode) plasmas at the outer limiters of the first wall using calibrated visible cameras. They are inferred from the measured radiances using the spectroscopic S/XB method. From the fluxes, the effective gross erosion yield Y eff of the limiter surface is estimated. After discussing the uncertainties in the proposed methodology, we show the dependence of the deduced particle fluxes and Y eff of recent JET L-mode plasmas on: separatrix–limiter clearance, magnetic field and plasma current, neutral beam injection and ion cyclotron resonance heating power, average plasma density and majority ion mass, hydrogen (H), deuterium (D) and tritium (T). The results are in general accord with prior edge plasma L-mode understanding. Finally, the obtained Y eff yields are discussed in view of updated SDTrim surface–particle interaction code calculations. The possible contribution of parasitic light due to reflections from the divertor is examined.

Abstract Luminous red novae are enigmatic transient events distinguished by a rapid rise in luminosity, a plateau in luminosity, and spectra, which become redder with time. The best-observed system before, during, and after the outburst is V1309 Sco. We model a candidate V1309 Sco progenitor binary configuration (1.52 + 0.16 M ⊙) using the smoothed particle hydrodynamics (SPH) code StarSmasher with a modified energy equation that implements flux-limited emission-diffusion radiative transport in a Lagrangian case. We developed an imaging technique allowing us to capture the flux an observer would measure. In this novel method, the outgoing radiative flux of each SPH particle in the observer's direction is attenuated by other particles along the path to the observer. We investigated how the light curve is affected in various models: with and without dust formation; constant, Planck, or Rosseland mean opacities; different donor star sizes; different companion star masses and types; radiative heating included in our modified energy equation; and different SPH simulation resolutions. The resulting evolution in bolometric luminosity and spectrum peak temperature is in good agreement with V1309 Sco observations. Our simulations rule out V1309 Sco models that do not assume dust formation.

In the ongoing U.S. project, “Liquid Metal Plasma Facing Components,” sponsored by the U.S. Department of Energy, efforts have been taken to develop two open-surface divertor designs for the Fusion Nuclear Science Facility using liquid lithium (Li) as a heat and particle flux removal media. The main focus of this study is the design and analysis of a slow (~1 mm/s) and thin (<1 mm) open-surface Li flow divertor with a Li-cooled substrate, which is then compared with an earlier design of a fast (up to 10 m/s) and thick (~0.5 cm) Li flow divertor with the substrate cooled with helium. The slow Li flow divertor design is based on the original LiWall concept developed at the Princeton Plasma Physics Laboratory. Such a thin and slow Li layer can remove the particle flux by reducing the recycling flux, while the heat flux is removed mainly through the heat sink located beneath. In the present study, the heat sink is provided through a Li cooling flow inside the substrate of reduced activation ferritic/martensitic steel. By performing a multiphysics analysis with COMSOL that included liquid-metal magnetohydrodynamics (MHD), heat transfer, and structural mechanics, the impact of various factors on the divertor heat removal capability, such as Li flow velocity, MHD effects, and inlet velocity boundary condition, were examined. Based on comparisons of the two divertor designs, it was shown that the fast-flow divertor significantly outperformed the slow-flow design, whose heat removal capability was limited to ~1 to 2 MW/m2.

The paper presents the results of material testing for the purpose of obtaining radiator material – acomposite coating with neutron conversion material – for ionization chambers (IC) which contain the 6Li isotope and convert neutron radiation to a flux of high-energy charged particles through the 6Li(n, α)3H nuclear reaction. The proposed method for forming lithium-containing radiator material allows ensuring a high temperature resistance of up to 600 °C and a mechanical strength at the expense of adhesion to the IC electrode material (grade 321 steel). The advantages of a lithium-containing radiator, compared to a boron radiator, are explained by the smaller cross-section of the 6Li-neutron interaction: the smaller efficiency of the "neutron → charged particle" conversion is made up for by a high power density and a prolonged free path of reaction products in the radiator material, which makes it possible to increase the surface density of 6Li atoms, while reducing the extent of "burnup" in neutron fields. The IC electrode radiator material consists of a two-layer composite coating comprising an adhesive silicate layer and a functional neutron-sensitive lithium fluoride layer. Measurements at an alpha spectrometric facility have shown that the coating has a high energy output (~ 2.8·10–3 MeV/neutron), which remains stable after four thermal cycles of up to 600 °C. The coating is resistant to vibration when exposed to frequencies of 35 to 200 Hz. The paper presents the results of testing the IC mockup with a lithium-containing radiator material. When irradiated with a neutron flux of 6·103 cm–2·s–1, the IC mockup sensitivity value was about 10–15A·s·cm2/neutron, which agrees with the calculated value.

Abstract Simulating plasma turbulence presents significant computational challenges due to the complex interplay of multi-scale dynamics. In this work, we investigate the use of convolutional neural networks to improve the efficiency of plasma turbulence simulations, focusing on the Hasegawa–Wakatani model. The networks are trained to learn the closure terms in large eddy simulations, providing a computationally cheaper alternative to the high-resolution numerical solvers for capturing the effects of high-frequency components. This study is the first to successfully apply machine learning to predict plasma behavior for adiabatic coefficients beyond the training range for the Hasegawa–Wakatani equations. We generate ground truth simulations for three values of the adiabatic coefficient ( C ∈ { 0.2 , 1.0 , 5.0 } ), and train our models on one, or two. The evaluation is then performed on the remaining values. The models generalize well and accurately predict the particle flux up to a factor 5 outside the training range. Finally, we address a key challenge in machine-learning-accelerated plasma simulations—initialization—by starting simulations for previously unseen adiabatic coefficients C with states from existing simulations at other known C values. This approach removes the need for expensive direct numerical simulations for initialization while maintaining physical accuracy and a fast convergence rate. Overall, the results highlight the model’s strong generalization capabilities and its potential for accelerating plasma turbulence simulations with more complex sets of parameters.

Abstract High ratio of kinetic to magnetic pressure, β, is a signature of good performance and hence desirable in tokamak plasmas. Optimizing plasma operation towards high β requires the integration of sources and transport physics modules in integrated modelling frameworks. Turbulent fluxes, which dominate the transport, are modelled using physics based reduced quasilinear model like trapped gyro Landau fluid (TGLF) (Staebler et al 2007 Phys. Plasmas 14 055909). The ability of TGLF to accurately predict turbulent transport at high β is assessed in a comparison against the higher fidelity gyrokinetic code GKW (Peeters et al 2009 Phys. Commun. 180 2650–72). The comparison is performed for an idealised case and for a JET-based high β case. The linear response of TGLF is verified and improved to better capture electromagnetic kinetic ballooning modes (KBMs). The quasi-linear fluxes computed with TGLF match within 75% the non-linear heat and particle fluxes computed with GKW for the component carried by electric potential fluctuations. The magnetic flutter component, however, is strongly underestimated. This study indicates that further improvements of the linear solver and refined saturation rules are needed to properly describe high-β electromagnetic turbulence. The general trends and thresholds with respect to the driving gradients are nevertheless captured. With these limitations in mind and using the recommended settings to properly describe KBMs, TGLF can be used in integrated modelling to explore high-β regimes.

Ground-Level Enhancements (GLEs) pose a potential hazard for crew and passengers on polar routes. The accurate estimation of the integral proton flux of Solar Energetic Particle (SEP) events is crucial for assessing the expected radiation dose. This paper describes a new approach that predicts the occurrence of GLEs and the associated &gt;500 MeV intensity using proton and electron data. The new approach utilizes the Geostationary Operational Environmental Satellites (GOESs) for proton observations and the Advanced Composition Explorer (ACE) satellite for electron observations. Núñez et al. proposed a GLE occurrence predictor called the High Energy Solar Particle Events foRecastIng and Analysis (HESPERIA) University of Málaga Solar particle Event Predictor (UMASEP-500), which did not include a model for predicting the &gt;500 MeV integral proton intensity. This paper presents a comparison in terms of the GLE event occurrence between the HESPERIA UMASEP-500 and a new approach called UMASEP-500. Although the new approach shows a slightly better critical success index (CSI), which combines the probability of detection (POD) and false alarm ratio (FAR), the difference is not statistically significant. The main advantage of the new UMASEP-500 is its ability to predict the expected &gt;500 MeV proton intensity. This study provides initial insight into a new era of electron and proton telescopes that will be available at L1 in the coming years.

Abstract We present a new framework for core-edge integration studies named SICAS (SOLPS-ITER coupled to ASTRA-STRAHL) which enables high fidelity simulations of the core, edge, and divertor regions encompassing the transport of ions as well as the impurities through the entire plasma domain. SICAS handles the exchanging of the particle and power fluxes as well as transport coefficients to ensure consistency through the codes. An overlapping region is defined from the inside of the separatrix of the plasma to the SOLPS-ITER core boundary allowing for matching profiles and fluxes between the two codes for a self-consistent approach. The results presented here demonstrated the flexibility of SICAS to simulate different configurations, scenarios, divertor geometries, and plasma species with good agreement with DIII-D experimental data. This tool opens new possibilities in integrated modeling of fusion devices integrating all relevant phenomena in the core and the divertor plasmas. These capabilities are required for the interpretation of current experiments as well as the design of new devices.

Abstract A transition from a divertor configuration to a limiter configuration and associated transient plasma oscillation were observed in configurations whose confinement region expanded with the codirected plasma current in the Heliotron J device. The transition was associated with the edge plasma profile such as electron density and temperature, and the change in the particle flux on the divertor probe was qualitatively consistent with the magnetic field line tracing calculation result, including the effect of the plasma current. During the transition, a spontaneous oscillation with a toroidal mode structure of n = 1 was observed at approximately 2 kHz, accompanied by an edge plasma response with a synchronized divertor footprint shift. This suggests that the transition to the limiter configuration was coupled with transient oscillatory responses. The study shows that the plasma current alters the edge magnetic field structure, and the edge plasma oscillates as a transient response.

Island formation in strain-free heteroepitaxial deposition of thin films is analyzed using kinetic Monte Carlo simulations of two minimal lattice models and scaling approaches. The transition from layer-by-layer (LBL) to island (ISL) growth is driven by a weaker binding strength of the substrate, which, in the kinetic model, is equivalent to an increased diffusivity of particles on the substrate compared to particles on the film. The LBL-ISL transition region is characterized by particle fluxes between layers 1 and 2 significantly exceeding the net flux between them, which sets a quasiequilibrium condition. Deposition on top of monolayer islands weakly contributes to the second-layer nucleation, in contrast with the homoepitaxial growth case. A thermodynamic approach for compact islands with one or two layers predicts the minimum size in which the second layer is stable. When this is linked to scaling expressions for submonolayer island deposition, the dependence of the ISL-LBL transition point on the kinetic parameters qualitatively matches the simulation results, with quantitative agreement in some parameter ranges. The transition occurs in the equilibrium regime of partial wetting, and the convergence of the transition point upon reducing the deposition rate is very slow and practically unattainable in experiments.

Muon collisions are considered a promising means for exploring the energy frontier, leading to a detailed study of the possible feasibility challenges. Beam intensities of the order of 1012 muons per bunch are needed to achieve the necessary luminosity, generating a high flux of secondary and tertiary particles from muons decay that reach both the machine elements and the detector region. To limit the impact of this background on the physics performance, tungsten shieldings have been studied. A machine learning-based approach to the geometry optimization of these shieldings will be discussed.

The dosimeter Liulin-MO for measuring the radiation environment on board the ExoMars Trace Gas Orbiter (TGO) is a module in the Fine Resolution Epithermal Neutron Detector (FREND). A number of solar energetic particle (SEP) events were observed in Mars orbit from July 2021 to 2024 during the increasing phase and close to the maximum of the 25th solar cycle activity. The results from the SEPs measurements obtained in 2021-2023 by Liulin-MO have been previously reported. Here we present the Liulin-MO results from the observation of the radiation parameters of the SEP events during January- October 2024. The most powerful SEP event registered up to now in TGO orbit started on 20 May 2024. The maximum dose rate during this SEP event has been 2800 ± 280 µGy h-1 and the maximum particle flux - 383 ± 19 cm-2 s-1. The total event lasted for about 64 hours up to 24 May with a long tail of increased dose rates and fluxes. The total dose from SEPs for the 64 hours of the main phase of the SEP event was 24.7 ± 2.5 mGy. The total dose from SEPs during this event is equal to the dose from the galactic cosmic rays (GCR) received for about 200 days at this phase of solar cycle 25. The total dose from all SEPs during January - September 2024 is 36.6 mGy (in Si), which is approximately equal to the dose received from GCR for the same period. The observations of SEPs in Mars orbit are compared to the observations during the same periods of proton fluxes measured by the GOES satellite in Earth orbit. The results show that some of the SEPs observed in Mars orbit, excluding the biggest SEP events of 20-24 May and 05-07 September, are also seen in the GOES proton fluxes data. SEP events recorded both in Mars and Earth orbits are related to coronal mass ejections (CMEs) observed by the SOHO and STEREO A coronagraphs. The paper shows that responsible for most of the SEP events registered both in the Liulin-MO data and in the GOES proton fluxes data are halo CMEs. The paper also shows that the sources of the three most powerful SEP events in Mars orbit - those of 20 May, 23 July and 05 September - are halo CMEs from the far side of the Sun. Some of these CMEs are associated with major X class far-side flares. Long-term investigations of the GCRs radiation parameters in Mars orbit show that in August 2024 (the last month of our data with no recorded SEP events) the dose rate was 6.5 ± 0.65 µGy h-1 and the particle flux - 1.4 ± 0.07 cm-2 s-1. These values are about 40 % of the corresponding maximal values measured by Liulin-MO during the solar cycle 24 minimum in March 2020. The above results show the importance of long-term measurements (at least during a full solar cycle) of the radiation conditions in Mars vicinity. Such measurements will make it possible to obtain the data necessary for the planning of future manned and robotic missions, as well as for the selection of the best time interval in the solar cycle for a manned flight to the planet.

A particle balance analysis was conducted during a deuterium (D2) shattered pellet injection-induced plasma shutdown on the DIII-D tokamak to determine why less than 20% of the pellet material is assimilated into the core plasma by the mid-current quench (CQ). Initially, most of the D2 is injected as frozen shards and ionized upon entering the vessel. During the thermal quench, ionized particles move to the divertors and subsequently to the center post (CP) walls, where they rapidly recycle and partially accumulate as neutrals without assimilating into the core plasma. In contrast, the particle flux to the outer midplane walls is negligible, despite being accompanied by hot plasma with electron temperatures exceeding 100 eV. During mid-CQ, volume recombination effects, although not large enough to impact overall particle balance, were significant enough to require accounting for accurate interpretation of fast-framing camera D-alpha signals and the estimation of the CP wall particle flux. In addition, toroidal asymmetries, observed in measurements of toroidal electron density perturbations and the phase of magnetohydrodynamic modes, are present throughout the shutdown and can account for a discrepancy in the assimilation rate for up to 50% of the observed D2 particle inventory. These sources and sinks of particles and fluxes were identified using absolutely calibrated D-alpha brightness and Langmuir probes.

The experiments carried out in hydrogen at the TOMAS facility show the possibility of controlling plasma parameters such as temperature and electron density in a combined electron cyclotron resonance and radio frequency (ECR+RF) discharge. A maximum plasma density of up to ≈6 × 1016 m−3 and electron temperature of up to 35 eV are observed in the combined ECR+RF discharge. The propagation of RF waves in hydrogen plasma under a weak magnetic field is analyzed. Depending on RF frequency and experimental conditions, such as radial distribution of plasma density and magnetic field, there can be several cases: only the slow wave can propagate, simultaneously slow and fast waves can propagate, or only the fast wave can propagate. The injection of additional RF power into the ECR discharge allows us to change the flux of neutral particles and their distribution function. Even the injection of small RF power of ≈ 0.26 kW relative to microwave power of ≈ 1.7 kW leads to an increase in the hydrogen flux by a factor of ∼2.5. At RF power PRF ≈ 1.57 kW, the H0 flux increases by a factor of ∼9.3. The ability to control the fluxes and energies of particles leaving the plasma volume is important to approach the conditions necessary to study plasma–surface interactions in wall conditioning and fusion edge plasmas.