Increase In Particle Flux Research Articles

Relation between the solar wind dynamic pressure at Voyager 2 and the energetic particle events at Voyager 1

Starting in 2001, Voyager 1 observed three events characterized by enhanced fluxes of energetic particles. These events suggest that Voyager 1 made a close approach to, or a crossing of, the termination shock. Although the plasma experiment on Voyager 1 is not providing useful data, plasma data from Voyager 2 may shed light on the plasma conditions at Voyager 1. Before the first particle event, Voyagers 1 and 2 see similar particle signatures. Voyager 2 pressure and energetic particle flux profiles have similar structure. The merged interaction regions (MIRs) observed at Voyager 2 have counterparts in the Voyager 1 data. We propagate solar wind data from Voyager 2 to Voyager 1 and show that at the predicted MIR arrival times, there is always a response in the Voyager 1 particle data. These effects vary, from an increase in particle flux to a rapid turnoff of the particle event. We discuss the observed energetic particle effects and how the MIRs produce them.

Plasma/Liquid-Metal Interactions During Tokamak Operation

One of the critical technological challenges of future tokamak fusion devices is the ability for plasma-facing components to handle both normal and abnormal plasma/surface interaction events that compromise their lifetime and operation of the machine. Under normal operation plasma/surface interactions that are important include: sputtering, particle implantation and recycling, He pumping and ELM (edge localized modes)-induced erosion. In abnormal or off-normal operation: disruptions and vertical displacement events (VDEs) are important. To extend PFC lifetime under these conditions, liquid-metals have been considered as candidate PFCs (Plasma-Facing Components), including: liquid lithium, tin-lithium, gallium and tin.Liquid lithium has been measured to have nonlinear increase of physical sputtering with rise in temperature. Such increase can be a result of exposure to ELM-level particle fluxes. The significant increase in particle flux to the divertor and nearby PFCs can enhance sputtering erosion by an order of magnitude or more. In addition from the standpoint of hydrogen recycling and helium pumping liquid lithium appears to be a good candidate plasma-facing material (PFM). Advanced designs of first wall and divertor systems propose the application of liquid-metals as an alternate PFC to contend with high-heat flux constraints of large-scale tokamak devices. Additional issues include PFC operation under disruptions and long temporal instabilities such as VDEs. A comprehensive two-fluid model is developed to integrate core and SOL (scrape-off layer) parameters during ELMs with PFC surface evolution using the HEIGHTS package. Special emphasis is made on the application of lithium as a candidate plasma-facing liquid-metal.

Magnetic storm ring current injection modeled with the Rice Convection Model and a self‐consistent magnetic field

We simulate plasma transport from the plasma sheet to the ring current, for the first time including the feedback effect of the drifting particles on both the electric and magnetic fields. Results suggest that strong, steady adiabatic convection throughout the middle plasma sheet leads to a highly stretched inner plasma sheet, but no ring current particle flux increases. We subsequently impose a substantial reduction of the specific entropy PV5/3 near midnight outside 10 RE, where P is particle pressure and V = ∫ds/B is flux tube volume. This produces a strong enhancement of the asymmetric ring current, which becomes symmetric when the pressure depletion and strong convection are quelled. We suggest that a reduction of the specific entropy in a region of the inner plasma sheet, apparently by some process that violates the assumption of adiabatic drift, plays a major role in the injection of a storm‐time ring current.

Substorm injection modeling with nondipolar, time‐dependent background field

We model energetic particle injections during substorms by investigating the particle interaction with an earthward propagating electromagnetic pulse of spatially localized transient electric (E) and magnetic (B) fields, superposed over a background B field. The current work extends our previous model by considering the background field to be nondipolar (stretched) before the arrival of the pulse (i.e., during the substorm growth phase), changing in a time‐dependent manner into a dipole field in the wake of the pulse. The particle motion still conserves the first adiabatic invariant, even in the stretched B field, and both protons and electrons are convected earthward by the E × B drift to regions of higher field, undergoing betatron acceleration. As in the previous model, we find fully analytical solutions for the gyrocenter motion of the 90° pitch angle particles, and we use them to compute the injected particle flux. We discuss how the model can explain several injection features such as the low/high energy cutoffs, and finally we apply the solutions to a simulation of an actual injection event, obtaining good agreement with observations. The current results with the more realistic background field show significant increase in particle flux for “substorm energies” (tens to hundreds of keVs) compared with the case of a dipole background, leading to the conclusion that the particles have to arrive from closer to Earth than before in order to explain the observed injected flux levels. The new model provides a better fit to observations than the previous one, since it requires lower transient E fields (more realistic of a typical substorm), and thus better explains the ubiquity of particle injections associated with substorms.

Dual spacecraft observations of a compression event within the Jovian magnetosphere: Signatures of externally triggered supercorotation?

By using Cassini as an upstream solar wind monitor, we are able to infer increases in the interplanetary dynamic pressure upstream of Jupiter as the spacecraft approached the planet. Observations are made of the effect that these pressure increases had upon both the fields and particles within the Jovian magnetosphere as measured by the Galileo orbiter, which had subsequently reentered the magnetosphere on the duskside. As the external pressure increased, so too did the total field magnitude at Galileo (in particular the Bz and Bϕ components). In addition, strongly leading field angles were observed following the onset of the compression and strongly lagging fields during reexpansion. These observations are consistent with the concept of external control of the angular velocity of the magnetospheric plasma due to conservation of angular momentum within the system. Heating of the plasma can be seen as a pronounced increase in particle flux as measured by the Energetic Particles Detector (EPD) instrument aboard Galileo. Changes in plasma velocity inferred from energetic particle anisotropies at Galileo appear to be consistent with the behavior of the changing magnetic field angle. The overall behavior and response time of the system appears to be consistent with recently published theoretical modeling of the Jovian magnetosphere‐ionosphere coupling system.

Development of the CMS pixel detector

A readout chip for the CMS pixel detector has been developed in the radiation hard DMILL process. The chips ability to operate under LHC conditions was tested in a high-rate pion beam with track densities up to 3×10 7 cm −2 s −1 . The observed degradation of the detection efficiency with increasing particle flux is compared with the data-loss mechanisms inherent to the readout architecture. First detector modules with 16 chips on a low-mass high-density interconnect are evaluated. The next iteration of the readout chip is designed for a 0.25 μm process with a radiation-tolerant layout.

Changes in Flow Direction at a Point Caused by Obstacles During Passage of a Density Current

The flow pattern and sediment character of laboratory density currents partly blocked by bed topography is used to demonstrate how changes in paleocurrent direction through a turbidite at a single site can be explained. These experiments confirm that a relatively small obstacle may affect bed thickness and paleocurrent patterns at considerable distances away from obstacles. Density currents generated by a lock-exchange mechanism spread radially across the tank floor and were partially blocked by a wedge-shaped obstacle with steep face (scarp) facing upstream. When the body of the current impinged on the obstacle, a thickened region of the flow developed upstream of the scarp, with increased entrainment of ambient fluid above it. The upflow edge of the thickened region was at a small angle to the obstacle front and propagated rapidly upflow and to the sides of the obstacle. Internal flow vectors observed with thread flags were radial from the lock before the head reached the obstacle. After the head passed the obstacle, flow vectors in the region of thickened flow upstream and to the sides of the obstacle were reoriented nearly parallel to the obstacle scarp. Thus flow vector at a point rotated by as much as 45° during passage of the current. The deposits of sediment-laden density currents thickened in the region of observed flow thickening because of an increased particle flux to the bed caused by velocity reduction. The upflow limit of the influence of the obstacle on deposition is marked by an abrupt increase in the thickness of the deposits. This area of thickening occurs in an area where the flow is accumulative.

Scavenging of 230Th, 231Pa and 10Be in the Southern Ocean (SW Pacific sector): the importance of particle flux, particle composition and advection

Abstract The scavenging of 230Th, 231Pa and 10Be was studied in the Pacific sector of the Southern Ocean along 170°W using measurements from surface sediments, time-series sediment traps, and the water column. All sediment traps collected an annual flux of 231Pa greater than the integrated rate of production by 235U-decay (up to 5.5 times greater) and a flux of 10Be greater than the global-average deposition rate of 10Be (up to 3.4 times greater). Fluxes of 230Th were on average close to the production rate in the overlying water column. These large fluxes of 231Pa and 10Be, and high unsupported 231Pa/231Th and 10Be/230Th ratios in the sediments, are not associated with depletion of nuclides in the water column, and therefore are not the result of the classical boundary scavenging mechanism. We estimate that of the 231Pa and 230Th advected into the Southern Ocean as part of the large-scale overturning circulation, only those nuclides associated with the “upper limb” of this circulation, i.e. those that pass through the surface as part of the wind-driven Ekman flow, are scavenged efficiently. The majority of the nuclides advected into the Southern Ocean and associated with the “bottom water limb” are not scavenged to the sediments of the Southern Ocean, but are returned northward. Throughout the year, the unsupported 231Pa/230Th and 10Be/230Th ratios of material reaching sediment traps at ∼1000 m at a given site increase with increasing particle flux. This behavior is explained by a conceptual model in which Th, Pa and Be are scavenged reversibly by fine-grained suspended particles at all depths, while Pa and Be are in addition scavenged strongly by diatom-rich aggregates in surface waters. Spatial variability in the annually averaged unsupported 231Pa/230Th and 10Be/230Th ratios of sinking particulate matter reflects primarily the variability in particle composition, and in the ratio and quantity of nuclides upwelled to the mixed layer, rather than variability in particle flux.

Temporal variability of deep-sea zooplankton in the Arabian Sea

Mesozooplankton samples from two stations in the Arabian Sea (WAST, 4,050 m, 16°15′N, 60°20′E; CAST, 3,950 m, 14°30′N, 64°30′E) were collected from the surface down to 20 m above bottom during three monsoon periods: the autumn intermonsoon in October 1995, the spring intermonsoon in April 1997, and the NE monsoon in February 1998. The main goal of this study is to enhance our knowledge on the effect of spatial and temporal differences in primary production and particle flux rates on the abundance and distribution of mesozooplankton, with special attention to the deep sea. Literature data indicate episodically high rates of primary production and particle flux in the region during the SW monsoon and the autumn intermonsoon. Set in this context, the zooplankton showed an in-phase coupling in biomass and abundance with the primary production in the surface 150 m. In the mesopelagic realm (150–1,050 m), the seasonal coupling was less clear. In the bathypelagic zone, below 1,050 m, there was no evidence of in-phase coupling, though temporal differences in the distribution of zooplankton abundance and biomass with depth between seasons could be shown by an analysis of covariance and an a posteriori test. The results suggest that the bathypelagic community responds to increased particle flux rates, but with longer time gaps than in the epipelagic zone. This is probably due to longer development and response times of zooplankton in the cold, deep-water environment, independent of possible lateral advection processes.

Removal efficiency of the dinoflagellate Heterocapsa triquetra by phosphatic clay, and implications for the mitigation of harmful algal blooms

An increased incidence of harmful algal blooms (HABs) has been reported in nearshore coastal waters, including economically important aquaculture sites worldwide. This has generated interest in using ecologically inert clays as a means of mitigating HABs at relatively shallow enclosed mariculture sites. This proposed mitigation measure assumes that flocculation and accelerated sedi- mentation of large algal cells (dinoflagellates) occurs with the application of clays. The objective of the current research was to characterize suspended clay-algal interactions and in situ particle size in a laboratory application of the phosphatic clay IMC-P (1.8 µm mean equivalent spherical diameter, ESD) to a simulated Heterocapsa triquetra (14.7 µm mean ESD) bloom. Flow speed was adjusted to provide 2 contrasting regimes (mimicking possible field conditions). This research was conducted in a recirculating flume and used a novel in situ device, the small volume particle microsampler (SVPM), for particle size characterization. Results indicated that 100% of the thecate dinoflagellate H. triquetra was removed in 48 h by IMC-P in a low-flow ( 13 cm s -1 ) regime. The mechanism for algal removal is equivocal since SVPM filter photographs indicated that clay aggregated to form particles >3 µm, but did not aggregate with algal cells under the experimental conditions tested. At this particle size, the clay aggregates become available for retention with 100% efficiency on the gills of suspension-feeding bivalves, which could be seriously affected by the increased particle flux to the bottom. The mecha- nism of cell removal by clays has not been identified; however, it may occur via direct effects of clay on cell surface properties and swimming ability. Further investigations on the removal mechanism are required to predict the fate of cells in a field application of clay.

The influence of particle composition and particle flux on scavenging of Th, Pa and Be in the ocean

We have examined the relative affinity of Th, Pa and Be for sorption from seawater onto particles of variable composition (opal, carbonate, lithogenic particles and organic carbon). Nuclide concentrations in particles collected from time-series sediment traps were normalized by the dissolved nuclide concentration in the overlying water column in order to compute partition coefficients under conditions spanning a wide range of particle flux and particle composition. Our results suggest that the affinity of particles for Pa and Be increases with their increasing opal content and decreasing carbonate content, while the affinity of particles for Th increases with increasing carbonate content, and decreases with increasing opal content. We find no correlation between the aluminosilicate content of particles and their affinity for scavenging of any of these elements. Extrapolating to a pure CaCO 3 end member, the partition coefficient for Th (9.0×10 6 g g −1) is ∼40 times greater than for Pa, and roughly 100 times greater than for Be, whereas for a pure opal end member, the partition coefficient for Th (3.9×10 5 g g −1) is slightly less than that for Pa and Be. Partition coefficients decrease with increasing particle flux in open-ocean settings, but not in an ocean-margin region. This kinetic effect reflects the increasing contribution of unaltered surface material reaching the sediment traps as particle flux increases. The degree of fractionation between Pa and Th and between Be and Th depends on the opal:carbonate rain ratio. These results challenge the use of sedimentary 231Pa/ 230Th and 10Be/ 230Th ratios as simple proxies of particle flux. However, the strong dependence of nuclide scavenging on the opal:carbonate rain ratio may provide a needed tool for reconstructing past changes in planktonic community composition.

Correlations between the arrival directions of ultrahigh energy cosmic rays and the large-scale structure of the universe

We present the results of analyzing the arrival directions of cosmic rays with energies E0≥ 4×1017 eV and zenith angles θ≤45° detected at the Yakutsk setup during 1974–2000. It is shown that increased particle fluxes exceeding the anticipated random distribution levels by 4–5)σ arrive from the galactic plane at E0≈(2–4)×1018 eV and from the supergalactic plane at E0≥8×1018 eV.

Cosmic rays of energies E 0≥1019 eV and the large-scale structure of the universe

Arrival directions of cosmic rays with energies E 0≥1019 eV are analyzed in the supergalactic coordinates. It is shown that increased particle fluxes arrive from the supergalactic plane and regions symmetrically adjoining it at angles ±b SG≈6.5°. Relatively high densities of clusters of galaxies and quasars, which are related to the large-scale structure of the universe, are observed in these regions.

Trapping efficiencies of sediment traps from the deep Eastern North Atlantic:

Bottom-tethered sediment traps deployed in the deep eastern North Atlantic between 54°N 20°W and 33°N 20°W (L1, L2, L3), at the European continental margin at 49°N (OMEX) and off the Canary Islands (ESTOC) were investigated for the determination of 230Th trapping efficiencies. The ratios of 230Th flux measured in the traps (Fa) to the expected 230Th flux from the production rate of 230Th in the overlying water column (Fp) ranged between 0.09 and 1.26. For the traps with deployment periods >300 days the interannual variation of Fa/Fp ratios (different years but same location and water depth) were up to 10%, suggesting that the average 230Th flux to the sediment traps did not vary significantly. The influence of lateral advection on the 230Th flux was taken into account either by applying a mass balance of 230Th and 231Pa or by assuming a constant removal rate of 230Th from the water column, an assumption based on similar 230Th concentration-depth profiles observed at most locations investigated. 230Th trapping efficiencies were between 9 and 143%, showing a trend of increasing efficiencies with increasing water depth. No relation was found between current velocities and 230Th trapping efficiencies. Our investigations suggest that the observation of constant or even increasing particle flux rates with increasing water depths in several sediment trap arrays investigated may be a result of sediment trap biases. The correction for the trapping biases is important for the understanding of the regional differences in the particle flux in the eastern North Atlantic.

Increased Particle Fluxes at the INDEX Site Attributable to Simulated Benthic Disturbance

Increased Particle Fluxes at the INDEX Site Attributable to Simulated Benthic Disturbance

Increased Particle Fluxes at the INDEX Site Attributable to Simulated Benthic Disturbance

Particle fluxes were measured 7 m above the sea bottom during the predisturbance, disturbance, and postdisturbance periods by using time series sediment traps attached to seven deep-sea moorings deployed in the INDEX experiment site in the Central Indian Basin. The predisturbance particle fluxes varied between 22.3 to 55.1 mg m−2 day−1. Increased and variable particle fluxes were recorded by the sediment traps during the disturbance period. The increase observed was 0.5 to 4 times more than the background predisturbance fluxes. The increases in particle fluxes (∼4 times) recorded by the sediment trap located in the southwestern direction (DMS-1) were the greatest, which could be the result of preferential movement of resuspended particles generated during the deep-sea benthic disturbance along the general current direction prevailing in this area during the experimental period. Also, the traps located closer to the disturbance area recorded greater fluxes than did the traps far away, across the Deep Sea Sediment Resuspension System path. This variability in recorded particle fluxes by the traps around the disturbance area clearly indicates that physical characteristics such as grain size and density of the resuspended particles produced during the disturbance had an important effect on particle movement. The postdisturbance measurements during ∼5 days showed a reduction in particle fluxes of ∼50%, indicating rapid particle settlement.

Particle acceleration in the dynamic magnetotail

The acceleration of charged particles to suprathermal energies is investigated in the context of magnetospheric substorms. Ion and electron test particle orbits are studied in dynamically evolving fields obtained from a three-dimensional resistive magnetohydrodynamic (MHD) simulation of reconnection in the near magnetotail. The simulation leads to plasmoid formation and ejection into the distant tail and an earthward collapse of the field in the inner tail. Energization of particles takes place predominantly in the inner tail region earthward of the neutral line, rather than in the vicinity of the neutral line. The test particle studies reproduce major observed characteristics of energetic particle flux increases (“injections”) in the inner magnetotail; a fast rise, a limited energy range of the flux increases, and spatially varying delays between the onsets of ion and electron injections. Acceleration mechanisms include a “quasipotential” acceleration, resulting from nonadiabatic particle motion in the direction of the cross-tail electric field, as well as betatron and Fermi-type acceleration. The major source region for accelerated ions (electrons) in the hundreds of keV range is the central plasma sheet at the dawn (dusk) flank, outside the reconnection site. Since this source plasma is already hot and dense, a moderate energization by a factor of approximately 2 is sufficient to explain the observed increases in the energetic particle fluxes. Differences between ions and electrons at energies of a few tens of keV are found to be associated with differences in the bounce periods, which enables ions to circumvent the acceleration region, so that only electron fluxes in that energy range become enhanced.

Towards prediction of flux effects in powder blasting nozzles

The efficiency of solid-particle erosion generally decreases with increasing particle flux. The particles rebounding from the surface collide with incoming particles, which results in a decrease in their velocity and the inflicted damage. This effect, called ‘the fluxe effect’, was modelled by Anand et al. [K. Anand, S.K. Hovis, H. Conrad, R.O. Scattergood, Flux effects in solid particle erosion. Wear. Vol. 118, 1987, pp. 243–257.] with a single-parameter fit model. Although this fit parameter was assumed to be constant, experiments have yielded a wide range of values for it, making the model unsuitable for flux-effect predictions. This paper shows for one erosion process—glass by alumina particles—that the variation in the fit parameter correlates with the particle velocity. The obtained relation describes the flux-effect data of three types of nozzles with sizes from 1.5 to 12 mm. Within this erosion process it is suitable for interpolation between process conditions and nozzle sizes. This result may be seen as a first step to a universal model for prediction of flux effects for all types of erosion processes.

Divertor heat and particle flux due to ELMs in DIII-D and ASDEX-upgrade

The authors characterize the divertor target plate heat and particle fluxes that occur due to Edge-Localized-Modes (ELMs) during H-mode in DIII-D and ASDEX-Upgrade. During steady-state ELMing H-mode the fraction of main plasma stored energy lost with each ELM varies from 6% to 2% as input power increases above the H-mode power threshold. The ELM energy is deposited near the strikepoints on the divertor target plates in a fast time scale of {le} 1 ms. The spatial profile of the ELM heat pulse is flatter and broader, up to about a factor of 2, than that of the heat flux between ELMs. On ASDEX-Upgrade the inboard strike-point receives the greatest fraction, {ge} 75%, of ELM divertor heat flux, while on DIII-D the in/out split is nearly equal. The toroidal asymmetry of the heat pulse has produced a peaking factor on DIII-D of no more than 1.5. The particle flux, as measured by Langmuir probes, has also been found to be localized near the divertor strike-points. The increased particle flux during ELMs is a significant fraction of the total time-integrated divertor plate particle flux.

Divertor heat and particle flux due to ELMs in DIII-D and ASDEX-upgrade

We characterize the divertor target plate heat and particle fluxes that occur due to edge localized modes (ELMs) during H-mode in DIII-D and ASDEX-upgrade. During steady-state ELMing H-mode the fraction of main plasma stored energy lost with each ELM varies from 6% to 2% as input power increases above the H-mode power threshold. The ELM energy is deposited near the strikepoints on the divertor target plates in a fast time scale of ≤ 1 ms. The spatial profile of the ELM heat pulse is flatter and broader, up to about a factor of 2, than that of the heat flux between ELMs. On ASDEX-upgrade the inboard strike-point receives the greatest fraction, ≥ 75%, of ELM divertor heat flux, while on DIII-D the in/out split is nearly equal. The toroidal asymmetry of the heat pulse has produced a peaking factor on DIII-D of no more than 1.5. The particle flux, as measured by Langmuir probes, has also been found to be localized near the divertor strike-points. The increased particle flux during ELMs is a significant fraction of the total time-integrated divertor plate particle flux.