Radial Ion Transport Research Articles

Statistical Survey of Interchange Events in the Jovian Magnetosphere Using Juno Observations

AbstractInterchange instability is known to drive fast radial transport of electrons and ions in Jupiter's inner and middle magnetosphere. In this study, we conduct a statistical survey to evaluate the properties of energetic particles and plasma waves during interchange events using Juno data from 2016 to 2023. We present representative examples of interchange events followed by a statistical analysis of the spatial distribution, duration and spatial extent. Our survey indicates that interchange instability is predominant at M‐shells from 6 to 26, peaking near 17 with an average duration of minutes and a corresponding M‐shell width of <∼0.05. During interchange events, the associated plasma waves, such as whistler‐mode, Z‐mode, and electron cyclotron harmonic waves exhibit a distinct preferential location. These findings provide valuable insights into particle transport and the source region of plasma waves in the Jovian magnetosphere, as well as in other magnetized planets within and beyond our solar system.

Core density profile control by energetic ion anisotropy in LHD

Electron and impurity ion density profiles have been controlled by using tangential and perpendicular neutral beams for plasma heating in a stellarator/heliotron for the first time. Reduced anisotropy of stored energy for energetic ion En⊥/Enǁ has resulted in an inward electron and impurity transport, forming a core electron density peaking. Increased anisotropy leads to a flat or hollowed electron density profile with an impurity exhaust in a core region [Yoshinuma et al., Nucl. Fusion 49, 062002 (2009)]. A high confinement state of particles in LHD has yet to be achieved, except for a temporal state of an electron density peaking created by a pellet injection. As a pioneering and crucial research result, the operation of energetic ion anisotropy by neutral beams has newly demonstrated that the direction of the radial transport of bulk and impurity ions can be controlled. At the same time, the overall plasma performance rises in neutron flux and stored energy. On the other hand, the increase in the anisotropy flattens the density profile. This new finding holds promise for a control knob of nuclear fusion reactors to enhance fusion power output.

In situ Construction of Multifunctional Surface Coatings on Zinc Metal for Advanced Aqueous Zinc–Iodine Batteries

AbstractAqueous zinc–iodine batteries (Zn–I2) demonstrate great promise in large scale energy storage systems. However, their practical application faces significant challenges including dendrite formation, corrosion caused by polyiodine ions, and other side reactions at the zinc anode side. Herein, a facile and efficient pretreatment method for zinc anodes through the substitution reaction of Zn and SnF2 to create a dense and durable multifunctional surface layer (MSL). The MSL comprise tin (Sn) and ZnF2 phases on the zinc metal, in which Sn possesses good zinc affinity and a high hydrogen evolution overpotential, while ZnF2 provides pathways for radial ion transport. Importantly, both have a low binding energy with polyiodine ions, preventing the failure of the interface layer. Therefore, this interface layer can effectively mitigate zinc metal electrode dendrite formation, corrosion from polyiodine ions, and other side reactions induced by water, simultaneously. As a result, the Zn–I2 batteries performance is greatly improved and exhibited a stable cycling to 20 000 times with 80% capacity retention at a current density of 2 A g−1. Even the I2 loading is increased to 8 mg cm−2, it can still cycle stably for 5000 cycles with a capacity retention of 94%.

Melatonin Mediates the Regulation of Morphological and Anatomical Traits in Carex leucochlora under Continuous Salt Stress

Soil salinity is one of the most critical factors limiting plant growth and development. Carex leucochlora is an important turfgrass species with a wide distribution in northern China that is highly sensitive to salt stress, which impairs its development. Recently, melatonin has emerged as a nontoxic biomolecule that regulates growth and enhances salt tolerance in plants. In this study, the mechanism of melatonin’s regulation of plant growth and anatomical characteristics in C. leucochlora seedlings under continuous salt stress was explored. Our results indicated that salt stress strongly suppressed plant growth and leaf cell activity, inhibited root morphology and root activity, and negatively affected leaf and root anatomic structures in the seedlings. Conversely, melatonin (150 μmol L−1) pretreatment improved the detrimental effect of salt stress by restoring the morphology of the leaf, alleviating damage to the cell membrane, improving root activity, and altering the root architecture and plant growth attributes. Moreover, after 12 days of salt stress, anatomical observations of the leaf showed that the thickness of the leaf blade, vascular bundle area of the leaf main vein, vesicular cell area, thickness of the upper epidermis, and thickness of the lower epidermis were increased by 30.55, 15.63, 12.60, 16.76 and 27.53%, respectively, with melatonin under salinity. Melatonin treatment also showed an increase of 5.91, 7.59, 15.57, and 20.51% in epidermal thickness, vascular cylinder diameter, xylem vessel diameter, and pith cell diameter, respectively, compared with salt stress after 12 days. These results suggest that melatonin alleviated salt stress through augmenting seedling growth, leaf cell activity, and root characteristics, maintained the stability of anatomic traits to maintain chloroplast cell homeostasis, and also protected the vascular tissues to promote the radial transport of water and ions in the C. leucochlora seedlings. These modifications induced by the exogenous application of melatonin may help C. leucochlora to acclimate successfully to saline soils.

Evolutions of equatorial ring current ions during a magnetic storm

In this paper, we present evolutions of the phase space density (PSD) spectra of ring current (RC) ions based on observations made by Van Allen Probe B during a geomagnetic storm on 23–24 August 2016. By analyzing PSD spectra ratios from the initial phase to the main phase of the storm, we find that during the main phase, RC ions with low magnetic moment μ values can penetrate deeper into the magnetosphere than can those with high μ values, and that the μ range of PSD enhancement meets the relationship: S(O+) >S(He+) >S(H+). Based on simultaneously observed ULF waves, theoretical calculation suggests that the radial transport of RC ions into the deep inner magnetosphere is caused by drift-bounce resonance interactions, and the efficiency of these resonance interactions satisfies the relationship: η(O+) > η(He+) > η(H+), leading to the differences in μ range of PSD enhancement for different RC ions. In the recovery phase, the observed decay rates for different RC ions meet the relationship: R(O+) > R(He+) > R(H+), in accordance with previous theoretical calculations, i.e., the charge exchange lifetime of O+ is shorter than those of H+ and He+.

Characterizing time intermittency in non-diffusive fast ion transport through plasma turbulence

Turbulent fast ion transport has been investigated in astrophisycal, laboratory and fusion plasmas. When gyro- and drift-averaging across plasma structures manifest as non-markovian and non-local effects, this results in generally non-diffusive transport. The intermittency of the formation of these plasma structures, such as blobs, can potentially be reflected in the transport of the fast ions as well. In the TORPEX basic plasma device, a toroidal beam of suprathermal Li-6 ions is injected into electrostatic plasma turbulence. Conditional sampling techniques confirm turbulent E × B-drifts as physical driving mechanism of radial fast ion transport, which features sub-, super- or quasi-diffusive regimes depending on the fast ion energy and propagation time. To address the question of how far local intermittency is associated with each regime, we analyze characteristics of time-intermittency on an extensive set of local fast ion time-series across all observed regimes. Modeling the time-average fast ion profiles as the result of a meandering smaller instantaneous beam allows us to predict the skewness of such time-series based on their time-average. Comparisons with the skewness of simple two-valued time-series can yield relative indications towards certain transport regimes in our specific system, based on the differences in the size of the instantaneous fast ion beam.

A Missing Link in Radial Ion Transport: Ion Transporters in the Endodermis.

In higher plants, roots have important functions, such as the acquisition of water and ions, as well as transportation into the aerial parts of the plant via the xylem vessels. Radial ion transport in the root is strongly regulated in the endodermis, which is characterized by the presence of the Casparian strip (CS) and suberin lamellae. Although tremendous progress has been made with regard to the ion transporters and endodermal cells, little is known about the relationship between the ion transporters in the endodermis and ion homeostasis in aboveground tissues. This review summarizes the current knowledge about the location of the ion transporters (or channels) in the endodermis. We mainly discuss the effects of mutants related to the CS and/or suberin formation on the role of endodermal ion transporters in ion homeostasis. We also wish to emphasize the critical role of endodermal ion transporters in the regulation of radial ion transport in the root.

SOLPS 5.0 simulations of the high-field side divertor detachment of L-mode plasmas in ASDEX upgrade with convection-dominated radial SOL transport

Abstract SOLPS 5.0 simulations assuming convection-dominated radial ion transport show qualitative and quantitative agreement with measurements of detached high-field side (HFS) divertor conditions for unseeded low-power L-mode plasmas in ASDEX Upgrade, while simultaneously maintaining a reasonable match to the density and temperature measurements at the low-field side (LFS) and HFS midplanes within the scatter of the data. The decreased diffusive transport from the high-density region in the HFS divertor volume across the separatrix into the core enables spatial extension of the high-density front to above the X-point in agreement with spectroscopic measurements. The suppressed ion fuelling from this region into the core plasma allows increasing the neutral D2 fuelling to experimental levels, leading to agreement with the measured sub-divertor neutral fluxes within 30%. Detachment of the HFS divertor is observed as a significant decrease of the target ion flux and as reproduction of the characteristic roll-over behaviour of the integrated target ion current at increasing upstream density.

Evaluation of Spatial Resolution of Neutron Profile Monitor in LHD

The vertical neutron camera (VNC) has been developed to measure neutron emission profile in deuterium plasmas of the large helical device (LHD). The experiment on spatial resolution evaluation for VNC was carried out in November 2016 by using a 252 Cf neutron source of 800 MBq. The neutron source was introduced into the LHD vacuum vessel through an aluminum pipe from an upper diagnostics port to the equatorial plane. The source was placed at the following two positions. The first position is just on the cylindrical collimator axis, and the second position is in the middle of two neighboring collimator axes. The stilbene scintillation detectors are aligned radially at the collimator end to detect unscattered fast-neutrons generated in a deuterium plasma. The 3-D neutron transport calculations by using a general-purpose Monte Carlo N-particle code 6 reproduced the experimentally obtained neutron counting rate, indicating that VNC has sufficient spatial resolution and the crosstalk between two neighboring collimators is a fairly small fraction. It is expected that the VNC on LHD will function as a tool for the study on the radial transport of energetic ions.

A space-resolved extreme ultraviolet spectrometer for radial profile measurement of tungsten ions in the Experimental Advanced Superconducting Tokamak

In order to study the radial transport of tungsten ions in long-pulse H-mode discharges, a space-resolved spectrometer working at 30–520 Å has been newly developed to measure a radial profile of the tungsten line emission. The spectrometer is installed behind a long extension vacuum tube connected to a horizontal midplane diagnostic port of EAST tokamak. The long distance between the plasma and spectrometer, 8835.5 mm, enables observation of the radial profile of impurity line emissions in a wide vertical range of −8.5≤Z≤ 40 cm (−0.1≤ρ≤0.6). A good spectral resolution of Δλ0=4−5 pixels at the foot position of spectral line profiles and a high spatial resolution of ΔZ=2.5 cm are obtained in addition to a sufficient temporal resolution, e.g. 50 ms/frame. As a result, accurate radial profiles have been successfully obtained in EAST Ohmic and H-mode discharges for several impurity species such as carbon, oxygen, argon, iron and tungsten. The radial profiles of tungsten line emissions from W42+ – W45+ ions with 4p–4s transitions measured at two wavelength ranges of 45–70 Å and 120–140 Å are analyzed for the ion density evaluation based on the photon emissivity coefficient from ADAS database. The result shows that the density of W43+ – W45+ ions ranges at 2–6 × 108 cm−3 in steady H-mode discharges with Te(0)=3 keV and ne(0)=4 × 1013 cm−3.

Bipolar to unipolar mode transition and imitation of metaplasticity in oxide based memristors with enhanced ionic conductivity

Neuromorphic engineering offers a promising route toward intelligent and low power computing systems that may find applications in artificial intelligence and the Internet. Construction of neuromorphic systems, however, requires scalable nanodevices that could implement the key functionalities of biological synapses. Here, we demonstrate an artificial synaptic device consisting of a Ti/yttria-stabilized-zirconia (ZrO2:Y)/Pt memristive structure, where the loss microstructure, high oxygen vacancy concentration, and resultant high ionic conductivity in ZrO2:Y facilitate the oxygen vacancy migration and filament evolution in the devices, leading to a bipolar artificial synapse with low forming and operation voltages. As the thickness of ZrO2:Y film increases, a transition from bipolar to unipolar resistive switching was observed, which can be ascribed to the competing vertical and radial ion transport dynamics. The emergence of unipolar switching has in turn allowed the device to exhibit metaplasticity, a history dependent plasticity that is important for memory and learning functions. This work thus demonstrates on-demand manipulation of ionic transport properties for building synaptic elements with rich functionalities.

Fusion neutron production with deuterium neutral beam injection and enhancement of energetic-particle physics study in the large helical device

The deuterium operation of the large helical device (LHD) heliotron started in March 7, 2017, after long-term preparation and commissioning works necessary to execute the deuterium experiment. A comprehensive set of neutron diagnostics was implemented to accelerate energetic-particle physics research in the LHD. The calibrated ex-vessel neutron flux monitor indicated that the total neutron emission rate in the first deuterium campaign reached 3.3 × 1015 n s−1 in inward shifted magnetic field configuration where confinement of helically trapped energetic ions is predicted to be better. Density dependence of measured total neutron emission rate was consistent with that predicted by the calculation. The neutron decay rate analysis following perpendicular deuterium beam blips injection suggested that the confinement of helically trapped beam ions can be understood by the classical slowing down model in relatively high-electron density plasmas at inward shifted magnetic field configuration. On the other hand, loss of helically-trapped beam ions was recognized even in the inward shifted configuration in the case of low density. Performance of the vertical neutron camera was verified by changing the plasma position and/or magnetic field strength. Drastic change of neutron emission profile was observed when the resistive interchange mode driven by helically-trapped beam ions appears. It was successfully demonstrated that the vertical neutron camera can play an important role in revealing radial transport and/or loss of beam ions. Triton burnup study was also conducted. In the first deuterium campaign, the maximum triton burnup ratio of 0.45% was obtained in inward shifted configuration. The burnup ratio decreased as a plasma was shifted outwardly as expected.

Observation of enhanced radial transport of energetic ion due to energetic particle mode destabilized by helically-trapped energetic ion in the Large Helical Device

A deuterium experiment was initiated to achieve higher-temperature and higher-density plasmas in March 2017 in the Large Helical Device (LHD). The central ion temperature notably increases compared with that in hydrogen experiments. However, an energetic particle mode called the helically-trapped energetic-ion-driven resistive interchange (EIC) mode is often excited by intensive perpendicular neutral beam injections on high ion-temperature discharges. The mode leads to significant decrease of the ion temperature or to limiting the sustainment of the high ion-temperature state. To understand the effect of EIC on the energetic ion confinement, the radial transport of energetic ions is studied by means of the neutron flux monitor and vertical neutron camera newly installed on the LHD. Decreases of the line-integrated neutron profile in core channels show that helically-trapped energetic ions are lost from the plasma.

Transport modeling of convection dominated helicon discharges in Proto-MPEX with the B2.5-Eirene code

Data-constrained interpretative analyses of plasma transport in convection dominated helicon discharges in the Proto-MPEX linear device, and predictive calculations with additional Electron Cyclotron Heating/Electron Bernstein Wave (ECH/EBW) heating, are reported. The B2.5-Eirene code, in which the multi-fluid plasma code B2.5 is coupled to the kinetic Monte Carlo neutrals code Eirene, is used to fit double Langmuir probe measurements and fast camera data in front of a stainless-steel target. The absorbed helicon and ECH power (11 kW) and spatially constant anomalous transport coefficients that are deduced from fitting of the probe and optical data are additionally used for predictive simulations of complete axial distributions of the densities, temperatures, plasma flow velocities, particle and energy fluxes, and possible effects of alternate fueling and pumping scenarios. The somewhat hollow electron density and temperature radial profiles from the probe data suggest that Trivelpiece-Gould wave absorption is the dominant helicon electron heating source in the discharges analyzed here. There is no external ion heating, but the corresponding calculated ion temperature radial profile is not hollow. Rather it reflects ion heating by the electron-ion equilibration terms in the energy balance equations and ion radial transport resulting from the hollow density profile. With the absorbed power and the transport model deduced from fitting the sheath limited discharge data, calculated conduction limited higher recycling conditions were produced by reducing the pumping and increasing the gas fueling rate, resulting in an approximate doubling of the target ion flux and reduction of the target heat flux.

Edge plasma responses to energetic-particle-driven MHD instability in Heliotron J

Two different responses to an energetic-particle-driven magnetohydrodynamic (MHD) instability, modulation of the turbulence amplitude associated with the MHD instability and dynamical changes in the radial electric field (Er) synchronized with bursting MHD activities, are found around the edge plasma in neutral beam injection (NBI) heated plasmas of the Heliotron J device using multiple Langmuir probes. The nonlinear phase relationship between the MHD activity and broadband fluctuation is found from bicoherence and envelope analysis applied to the probe signals. The structural changes of the Er profile appear in perfect synchronization with the periodic MHD activities, and radial transport of fast ions are observed around the last closed flux surface as a radial delay of the ion saturation current signals. Moreover, distortion of the MHD mode structure is clarified in each cycle of the MHD activities using beam emission spectroscopy diagnostics, suggesting that the fast ion distribution in real and/or velocity spaces is distorted in the core plasma, which can modify the radial electric field structure through a redistribution process of the fast ions. These observations suggest that such effects as a nonlinear coupling with turbulence and/or the modification of radial electric field profiles are important and should be incorporated into the study of energetic particle driven instabilities in burning plasma physics.

Direct measurements of classical and enhanced gradient-aligned cross-field ion flows in a helicon plasma source using laser-induced fluorescence

Direct laser induced fluorescence measurements are shown of cross-field ion flows normal to an absorbing boundary that is aligned parallel to the axial magnetic field in a helicon plasma. We show Langmuir and emissive probe measurements of local density and plasma potential in the same region, as well as floating probe spectra near the boundary. With these measurements, we investigate the influence of ion-neutral collisionality on radial ion transport by varying the ratio of the ion gyro-radius, ρi, to the ion-neutral collision length, λ, over the range 0.34 ≤ ρiλ−1 ≤ 1.60. Classical drift-diffusion transport along density and potential gradients is sufficient to describe flow profiles for most cases. For two parameter regimes (ρiλ−1 = 0.65 and 0.44), low-frequency electrostatic fluctuations (f < 10 kHz) and enhanced cross-field bulk ion flow to the boundary are observed.

A ULF wave driver of ring current energization

AbstractULF wave radial diffusion plays an important role in the transport of energetic electrons in the outer radiation belt, yet similar ring current transport is seldom considered even though ions satisfy a nearly identical drift resonance condition albeit without the relativistic correction. By examining the correlation between ULF wave power and the response of the ring current, characterized by Dst, we demonstrate a definite correlation between ULF wave power and Dst. Significantly, the lagged correlation peaks such that ULF waves precede the response of the ring current and Dst. We suggest that this correlation is the result of enhanced radial transport and energization of ring current ions through drift resonance and ULF wave radial diffusion of ring current ions. An analysis and comparison of the ion and electron diffusion coefficients further support this conclusion, ULF waves providing an important missing physical transport process explaining Dst underestimation in ring current models.

Pitch-angle distribution of TAE-induced losses of ICRH accelerated ions on JET

Experiments aiming to study the loss of energetic ions carried out in JET using low density plasmas and on-axis minority ion cyclotron resonance heating (ICRH) have been reported in Nabais et al (2010 Nucl. Fusion 50 115006). Though the fast ions accelerated by on-axis ICRH have a distribution in the normalized magnetic moment centred at Λ = 1, experimental measurements have shown that the fast ions whose loss is triggered by tornado modes (toroidal Alfvén eigenmodes (TAE) localized inside the q = 1 surface) reach the scintillator cup with an average Λ significantly higher than one (Λ = 1.1). On the other hand, the losses associated with the presence of TAE localized on the plasma boundary reach the scintillator cup with an average Λ slightly below unity. Since Λ increases while the fast ions drift radially outward due to resonant interaction with the Alfvénic modes, the high values of Λ characterizing the losses triggered by tornado modes indicate these ions have experienced a large radial displacement before being lost, i.e. they were originally localized in the plasma core. These experimental results corroborate the conclusion from Nabais et al (2012 Nucl. Fusion 52 083021) that the combined action of modes localized at different radial locations can lead to large radial transport and loss of ions originally localized in the plasma core. The results presented here also show that measurements of the pitch angle may be used to extract information about the original location of the ions reaching the scintillator cup.

Simulation Study of Alfvén-Eigenmode-Induced Energetic Ion Transport in LHD

The interaction between toroidal Alfven eigenmode (TAE) and energetic ions in the Large Helical Device (LHD) is investigated using a reduced version of theMEGA code that implements a realistic equilibriummagnetic field with the HINT code and corresponding TAE profile with the AE3D code. In simulations, the linear growth rate of TAE amplitude is proportional to energetic ion density; consequently, the nonlinear saturation level of the TAE amplitude is enhanced by the increase in the energetic ion density. Energy transfer analysis is performed to clarify destabilization and saturation mechanisms of the TAE and to identify resonant energetic ions. An analysis of test particles in the electromagnetic field perturbed by the TAE shows that the magnitude of fluctuations in the energetic ion orbits is proportional to the square root of the TAE amplitude. Our results qualitatively reproduce the radial transport of energetic ions by the TAE in the LHD.

Poloidal distribution of recycling sources and core plasma fueling in DIII-D, ASDEX-Upgrade and JET L-mode plasmas

Deuterium fueling profiles across the separatrix have been calculated with the edge fluid codes UEDGE, SOLPS and EDGE2D/EIRENE for lower single null, ohmic and low-confinement plasmas in DIII-D, ASDEX Upgrade and JET. The fueling profiles generally peak near the divertor x-point, and broader profiles are predicted for the open divertor geometry and horizontal targets in DIII-D than for the more closed geometries and vertical targets in AUG and JET. Significant fueling from the low-field side midplane may also occur when assuming strong radial ion transport in the far scrape-off layer. The dependence of the fueling profiles on upstream density is investigated for all three devices, and between the different codes for a single device. The validity of the predictions is assessed for the DIII-D configuration by comparing the measured ion current to the main chamber walls at the low-field side and divertor targets, and deuterium emission profiles across the divertor legs, and the high-field and low-field side midplane regions to those calculated by UEDGE and SOLPS.