Diamagnetic Drift Research Articles

Mass dependency of high-wavenumber turbulence in a linear partially magnetized plasma

We investigated the mass dependency of the high-wavenumber turbulence, which occurs at scales smaller than the ion effective Larmor radius, in a partially magnetized plasma column. In this system, two different types of fluctuations were observed: one exhibiting a coherent discrete spectrum, while the other displaying a broadband continuous spectrum. The phase velocities of both types showed a similar mass dependency, approximately matching the ion sound velocity or electron diamagnetic drift velocity. Additionally, we found that the discrete spectrum has a peak interval frequency comparable to the ion cyclotron frequency, which is consistent with ion cyclotron ranges of fluctuations, including ion Bernstein waves.

Tilted dust-acoustic waves in low-pressure DC complex plasma

This study utilized the ground-based Plasmakristall-4 experiment to investigate the characteristics of dust-acoustic waves in low-pressure neon plasma generated through a direct current discharge. The experimental observations revealed the presence of dust-acoustic waves exhibiting a distinctive screw-like wavefront structure. Interestingly, the phase speed of these waves was slightly higher than the theoretical predictions. This deviation can be attributed to the influence of external forces and boundary conditions, which introduce asymmetry to the system and result in the deformation of wave patterns. To gain further insight, a comprehensive three-dimensional particle drift path reconstruction was conducted, providing a clearer understanding of the observed phenomena and confirming the findings obtained through the experimental analysis.

Real-time polarization compensation method in quantum communication based on channel Muller parameters detection

Polarization drift in fiber and free-space optical links is a major factor in the dynamic increase of bit error rate in polarization-coded quantum key distribution (QKD) systems. A dynamic polarization compensation method applicable to both links is a challenge. Here we propose a universally applicable real-time polarization compensation method, that the Muller parameters of the optical links are first detected using a polarization detector, and then the optimal parameters of the controller are obtained by gradient descent algorithm. Simulation results indicate advantages over current methods, with fewer waveplates, faster speed, and wider applicability for various optical links. In equivalent experiments of both satellite and fiber optical links, the average polarization extinction ratio of 27.9 dB and 32.2 dB are respectively achieved. The successful implementation of our method will contribute to the real-time polarization design of fiber and free-space QKD systems, while also contributing to the design of laser-based polarization systems.

Charged particle collisionless transport near the X-point of the two-wire model

Collisionless charged particle motion and its transport in the two-wire model (TWM) with no axial magnetic fields is investigated numerically. The TWM configuration contains a magnetic X-point, and single particle motions in such a field have two conserved quantities: the total kinetic energy and the base field line value which is a quantity derived from the axial canonical momentum. As gyrating particles travel along the field lines, they may reach near the X-point region where the magnetic moment, the first adiabatic invariant, can be occasionally shifted due to a large gradient of the field. When the magnetic moment becomes large, resulting in a large Larmor radius, particles probabilistically cross the X-point to migrate to the opposite side of the TWM configuration. These phenomena are investigated with single particle simulations. We find that the statistical behaviour of the seemingly chaotic magnetic moment shifts are completely determined by the two aforementioned conserved quantities, and also that there exists a threshold energy, determined by the base field line value, allowing only particles with a higher energy to cross the separatrix and migrate. It is found that the crossing time is distributed exponentially, and that the migration confinement time, which is the average crossing time, is shorter for particles with a base field line closer to the separatrix and a higher energy. We provide an empirical expression, derived with the simulations, for estimating the collisionless migration confinement time.

Cotton (Gossypium hirsutum) Response to Plant Protection Products using Different Spray Nozzles

Application of dicamba to dicamba-tolerant cotton (Gossypium hirsutism L.) cultivars (Xtend Cotton, Bayer Crop Science, Research Triangle Park, NC) requires use of nozzles that deliver large spray droplets to avoid off-site movement through particle drift onto susceptible crops and other plants including endangered species. Twenty trials over a three-year period were conducted to determine if nozzles required to deliver dicamba plus glyphosate would be equally effective in delivering other pesticides including the herbicide glufosinate, the plant growth regulator mepiquat chloride, the insecticide bifenthrin plus dichrotophos and co-application of ethephon plus thidiazuron plus tribufos for removal of cotton foliage to improve harvest efficiency. Agrichemicals were applied using: a) Air Induction (AI) nozzles for agrichemicals except dicamba plus glyphosate b) Turbo Teejet Induction (TTI) nozzles for all agrichemicals c) TTI nozzles for glufosinate and dicamba plus glyphosate and AI nozzles for other agrichemicals. Applications were made in 145 L/ha at 152 kPa at a ground speed of 5 km/h. Cotton height at the end of the season, node above first fruiting branch, nodes above cracked boll, node of uppermost boll, total nodes, lint yield, and cotton fiber quality were similar regardless of nozzles used to deliver agrichemcials. Control of a complex of broadleaf signal grass (Urochloa platyphylla L.), goosegrass [Eleusine indica (L.) Gaert.], and large crabgrass (Digitaria sanguinalis L.) and Palmer amaranth (Amaranthus palmeri Watts.) was slightly lower when glufosinate was applied with TTI nozzles rather than AI nozzles. However, control of these weeds was similar regardless of nozzle selection when dicamba plus glyphosate was applied after glufosinate. These results suggest that growers can use nozzles that limit off-site movement through particle drift of agrichemicals throughout the cropping cycle with no major adverse effect on weed control and cotton growth and yield.

"Peanut (Arachis hypogaea) Response to Fungicides and Herbicides Applied using Different Spray Nozzles"

Late leaf spot [caused by Nothopassalora personata (Berk. & M.A. Curtis) U. Braun, C. Nakash, Videira & Crous] is an economically important disease in peanut (Arachis hypogaea L.) and fungicides are used routinely to protect peanut from infection and the resulting yield loss. Herbicides are an important component of effective weed management in peanut. Concern over particle drift of pesticides exists in the farming community, especially after stewardship issues associated with synthetic auxin application in herbicide resistant crops in the United States. Spray nozzles that deliver larger droplets that are less prone to drift is a possible solution to this issue. However, fungicides may be less effective in penetrating the crop canopy and covering foliage for protection from pathogens with these nozzles compared with nozzles delivering smaller droplets. Research was conducted to compare suppression of late leaf spot disease when chlorothalonil, prothioconazole plus tebuconazole, azoxystrobin, pyraclostrobin, and chlorothalonil were applied sequentially every 14 days using hollow cone nozzles (fine droplet size), regular flat fan nozzles (medium droplet size), air induction flat fan nozzles (coarse droplet size), and turbo teejet induction nozzles (ultra-coarse droplet size). Regular flat fan and hollow cone nozzles were slightly more effective in delivering fungicides based on canopy defoliation at harvest compared with turbo teejet induction nozzles and in some cases air induction nozzles. However, suppression of pathogens by fungicides applied using all four nozzle types prevented canopy defoliation adequately to protect peanut from yield loss. In a separate experiment, peanut yield and control of common ragweed (Ambrosia artemisiifolia L.) and late leaf spot did not differ at harvest when herbicides and fungicides were applied with air induction or turbo teejet induction nozzles throughout the cropping cycle. These results indicate that farmers can apply fungicides and herbicides to peanut using nozzles that limit potential for particle drift with minimal concern over reduced pesticide efficacy and protection of yield from pests.

3D cylindrical BGK model of electron phase-space holes with finite velocity and polarization drift

Nonlinear kinetic structures, called electron phase-space holes (EHs), are regularly observed in space and experimental magnetized plasmas. The existence of EHs is conditioned and varies according to the ambient magnetic field and the parameters of the electron beam(s) that may generate them. The objective of this paper is to extend the 3D Bernstein–Greene–Kruskal model with cylindrical geometry developed by L.-J. Chen et al. [“Bernstein–Greene–Kruskal solitary waves in three-dimensional magnetized plasma,” Phys. Rev. E 69, 055401 (2004)] and L.-J. Chen et al., [“On the width-amplitude inequality of electron phase space holes,” J. Geophys. Res. 110, A09211 (2005)] to include simultaneously finite effects due to (i) the strength of the ambient magnetic field B0, by modifying the Poisson equation with a term derived from the electron polarization current, and (ii) the drift velocity ue of the background plasma electrons with respect to the EH, by considering velocity-shifted Maxwellian distributions for the boundary conditions. This allows us to more realistically determine the distributions of trapped and passing particles forming the EHs, as well as the width-amplitude relationships for their existence.

Isotope effects on transport characteristics of edge and core plasmas heated by neutral beam injection (NBI) in an inward shifted configuration at the Large Helical Device

Isotope effects have been investigated in Neutral Beam Injection (NBI) heated plasmas on the Large Helical Device with similar operational parameters between Hydrogen (H) and Deuterium (D) plasmas. Experimental results show that the global energy confinement has no significant dependence on the isotope mass under similar discharge conditions with nearly the same heating power, line-averaged density ( nˉe ) and magnetic field. For both electron and ion energy transport, the transport coefficients, which are obtained based on local power balance analysis, have analogous profiles between H and D dominant plasmas. For neoclassical χe and χi values, they are almost equal between H and D dominant plasmas in low nˉe discharges, whereas in high nˉe cases they are lower in H plasmas than those in D ones. At low nˉe , the electron and ion thermal transport in both H and D plasmas are dominated by neoclassical transport at a certain zone ( ρ≈0.6−0.85 ), while the anomalous transport process has primary effects in the remaining area, and the density fluctuations exhibit ion temperature gradient mode nature. With increase of nˉe , the anomalous transport becomes prevailing and the density fluctuations propagate along electron diamagnetic drift direction. Bispectral analysis reveals that the H plasma has stronger nonlinear coupling in edge density fluctuations in both low and high density discharges, which is probably due to that the D plasma has stronger damping rate for the nonlinear interaction of turbulence. For a comparative study, the present results have been compared with those observed in the ECRH discharges (Tanaka et al 2019 Nucl. Fusion 59 126040). The reasons for the similarities and dissimilarities between these two different heating manners are not clear yet. To unravel the underlying physics, essential inputs from theories and simulations are required.

Bursting core-localized ellipticity-induced Alfvén eigenmodes driven by energetic electrons during EAST ohmic discharges

A series of high-frequency ( 400∼1000 kHz ) bursting core-localized Alfvén instabilities have been observed during ohmic discharges in EAST tokamak. The instability trigger favours the discharge conditions of low toroidal magnetic field and low electron density. The toroidal mode numbers are mainly n=2∼3 and they propagate in the ion diamagnetic drift (co-current) direction. These modes are radially localized in the range of ρtor=0.2∼0.35 based on Doppler BackScatter measurement. They are identified as ellipticity-induced Alfvén eigenmodes (EAEs) occurring at q=1 rational surfaces by magnetohydrodynamics simulations using the realistic geometry and plasma profiles. The EAEs show regular bursts with ∼10 ms duration along with the mode frequency chirping downwards and upwards rapidly. It is also found that sawtooth events can interrupt the growth and evolution of the EAEs, causing the modes to disappear immediately. Passing energetic electrons (EEs) that move much faster than Alfvén velocity are responsible for the destabilization of these EAEs, which attribute to the fact that the large poloidal and toroidal frequencies mostly cancel each other and satisfy the EAE resonance condition with primary energy exchange. These novel experimental results of the wave-particle interaction between EAEs and EEs are helpful for extrapolating alpha particle physics that are characterized by small orbit width with respect to machine size in future fusion reactors.

Effects of diamagnetic drift on nonlinear interaction between multi-helicity neoclassical tearing modes

A numerical study of the diamagnetic drift effect on the nonlinear interaction between multi-helicity neoclassical tearing modes (NTMs) is carried out using a set of four-field equations including two-fluid effects. The results show that, in contrast to the single-fluid case, 5/3 NTM cannot be completely suppressed by 3/2 NTM with diamagnetic drift flow. Both modes exhibit oscillation and coexist in the saturated phase. To better understand the effect of the diamagnetic drift flow on multiple-helicity NTMs, the influence of typical relevant parameters is investigated. It is found that the average saturated magnetic island width increases with increasing bootstrap current fraction f b but decreases with the ion skin depth δ. In addition, as the ratio of parallel to perpendicular transport coefficients χ ∥/χ ⊥ increases, the average saturated magnetic island widths of the 3/2 and 5/3 NTMs increase. The underlying mechanisms behind these observations are discussed in detail.

Electron energization in reconnection: Eulerian vs Lagrangian perspectives

Particle energization due to magnetic reconnection is an important unsolved problem for myriad space and astrophysical plasmas. Electron energization in magnetic reconnection has traditionally been examined from a particle, or Lagrangian, perspective using particle-in-cell (PIC) simulations. Guiding-center analyses of ensembles of PIC particles have suggested that Fermi (curvature drift) acceleration and direct acceleration via the reconnection electric field are the primary electron energization mechanisms. However, both PIC guiding-center ensemble analyses and spacecraft observations are performed in an Eulerian perspective. For this work, we employ the continuum Vlasov–Maxwell solver within the Gkeyll simulation framework to reexamine electron energization from a kinetic continuum, Eulerian, perspective. We separately examine the contribution of each drift energization component to determine the dominant electron energization mechanisms in a moderate guide-field Gkeyll reconnection simulation. In the Eulerian perspective, we find that the diamagnetic and agyrotropic drifts are the primary electron energization mechanisms away from the reconnection x-point, where direct acceleration dominates. We compare the Eulerian (Vlasov Gkeyll) results with the wisdom gained from Lagrangian (PIC) analyses.

Competition between drift and topological transport of colloidal particles in twisted magnetic patterns

We simulate the motion of paramagnetic particles between two magnetic patterns with hexagonal symmetry that are twisted at a magic angle. The resulting Morié pattern develops flat channels in the magnetic potential along which colloidal particles can be transported via a drift force of magnitude larger than a critical value. Colloidal transport is also possible via modulation loops of a uniform external field with time varying orientation, in which case the transport is topologically protected. Drift and topological transport compete or cooperate giving rise to several transport modes. Cooperation makes it possible to move particles at drift forces weaker than the critical force. At supercritical drift forces the competition between the transport modes results e.g. in an increase of the average speed of the particles in integer steps and in the occurrence of subharmonic responses. We characterize the system with a dynamical phase diagram of the average particle speed as a function of the direction of the topological transport and the magnitude of the drift force.

STEVE Events With FUV Emissions

AbstractSTEVE, Strong Thermal Emission Velocity Enhancement, was often observed by ground‐based imagers in visible wavelengths and rarely detected by global FUV imagers. We present a new event, and revisit two reported STEVE events, that were observed by the DMSP/SSUSI FUV imager at O 135.6 nm, N2 LBHS, and LBHL emissions. Coincident particle and plasma drift observations showed that the events were associated with high ion drift speed, low ion density and no energetic particle precipitation. This is consistent with earlier findings (e.g., MacDonald et al., 2018, https://doi.org/10.1126/sciadv.aaq0030; Gallardo‐Lacourt et al., 2018a, https://doi.org/10.1029/2018ja025368, 2018b, https://doi.org/10.1029/2018gl078509; Archer et al., 2019). In this paper, several new features are identified: (a) Detection rates of FUV STEVE are much lower than that of visible STEVE; (b) The STEVE on 27 March 2008 covers 3‐hr local time with a length up to 2,700 km around 60° magnetic latitudes; (c) Different widths of STEVE observed in O 135.6 nm and N2 LBH images indicate a large altitude range in the STEVE FUV emissions; (d) The true ion (assuming O+) drift speeds during the 27 March 2008 STEVE event could be up to 20 km/s, well above the DMSP SSIES sensor limit. The kinetic energy of the high speed ions is larger than the excitation potential of the observed FUV emissions; (e) The requirement of such extreme high ion drift speed explains why FUV STEVE have been rarely observed, compared to the visible STEVE; (f) The three FUV STEVE events occurred during moderate geomagnetic activity; (g) Theses events were conjugate in both hemispheres.

Effect of ion stress on properties of magnetized plasma sheath

In the plasma sheath, there is a significant gradient in ion velocity, resulting in strong stress on ions treated as a fluid. This aspect has often been neglected in previous sheath studies. This study is based on the Braginskii plasma transport theory and establishes a 1D3V sheath fluid model that takes into account the ion stress effect. Under the assumption that ions undergo both electric and diamagnetic drift in the presheath region, self-consistent boundary conditions, including the ion Bohm velocity, are derived based on the property of the Sagdeev pseudopotential. Furthermore, assuming that the electron velocity at the wall follows a truncated Maxwell distribution, the wall floating potential is calculated, leading to a more accurate sheath thickness estimation. The results show that ion stress significantly reduces the sheath thickness, enhances ion Bohm velocity, wall floating potential, and ion flux at the wall. It hinders the acceleration of ions within the sheath, leading to notable alterations in the particle density profiles within the sheath. Further research indicates that in ion stress, bulk viscous stress has the greatest impact on sheath properties.

Ion temperature dynamics for the edge and scrape-off layer plasma turbulence: role of gyro-viscosity and vorticity

In the presence of magnetic curvature and density/pressure inhomogeneity, the edge and scrape-off layer (SOL) regions of a tokamak plasma are highly turbulent mainly because of the drift/interchange instability mechanisms. The divergence of ion polarization drift contains the ion diamagnetic drift and E⃗×B⃗ drift velocity to define the plasma vorticity and convection of fluid, which can be approximated in several ways using various combinations of these two drifts. Here, in this work, three different approximations are used to represent three different models and are solved numerically. The numerical results indicate that the basic results of turbulence like radial profiles, radial electric field gradients, fluctuation labels, and Reynolds stress are widely different from the three different models. As these models provide different results, therefore, one must be careful to use these approximations for the description of turbulence. This work may be useful in choosing appropriate approximations to include ion temperature gradients for the turbulence studies on tokamaks/stellarators. The role of gyro-viscosity for plasma turbulence has been identified in this work.

Polarization effects in higher-order guiding-centre Lagrangian dynamics

The extended guiding-centre Lagrangian equations of motion are derived by the Lie-transform perturbation method under the assumption of time-dependent and inhomogeneous electric and magnetic fields that satisfy the standard guiding-centre space–time orderings. Polarization effects are introduced into the Lagrangian dynamics by the inclusion of the polarization drift velocity in the guiding-centre velocity and the appearance of finite-Larmor-radius corrections in the guiding-centre Hamiltonian and guiding-centre Poisson bracket.

Pore-scale modelling of particle transport in a porous bed

A computational study was performed of the transport of both non-adhesive and adhesive particles in a porous bed with a body-centred cubic (BCC) structure. Pore-scale simulation of the flow within the porous bed was achieved through combining the immersed boundary method and the lattice Boltzmann method. Particle transport is computed using an adhesive discrete-element method based on a multi-time-scale soft-sphere model. The fluid flow results are validated by comparison with experimental data for dimensionless permeability of flow in a porous bed of spheres. For computations with non-adhesive particles, the particles are observed to drift to the centre of ‘channels’ in the BCC array, within which most of the fluid flow occurs. The mechanism of this inward drift was found to be related to the phenomenon of oscillatory clustering, which is an inertial drift mechanism observed for particles in a corrugated channel. A measure for particle drift into these channels was developed, and the time rate of change of this measure was found to compare closely with an approximate theoretical prediction based on oscillatory clustering theory. The drift measure was observed to be limited at long time by hold-up of outlier particles caught in long-duration collisions with the fixed bed particles in regions of low fluid velocity magnitude. Simulations with adhesive particles exhibited marked increase in collision duration, as well as inhibition of the tendency to drift toward the flow channels due to adhesive hold-up.

Effect of Surface Waves on Settling and Drifting of Microplastic Particles: A Laboratory Experiment

Particle trajectories and average settling and drift velocities of microplastic particles under wave action were studied in a linear wind-wave channel. A wave-maker and an airflow above the water surface created various hydrodynamic conditions. Particles of various shapes (isometric, flat, elongated) were used. The paper provides a brief overview of the theoretical approaches (dimensional analysis) used to study the transport of microplastics in the presence of surface waves and currents. Based on this, a characteristic of wave regimes and sets of experimental particles is given. Terminal settling velocities of the particles in a quiet fluid are 1.0–3.8 cm/s. They were obtained experimentally and may be of independent interest. The settling trajectories of 13 types of particles in 4 wave regimes were obtained and analyzed. According to Welch’s t-criterion (p < 0.05), the average particle settling rate in the presence of waves differs slightly from the terminal settling velocity, which is consistent with other works. The results indicate that the average horizontal (drift) velocity follows the velocity of the mean current. The presence of wind enhances horizontal transport due to the induction of drift current and drastically increases particle dispersion.

Active generation and control of radial electric field by local neutral beamlets injection in tokamaks

The radial electric field plays an important role in plasma confinement in tokamaks and can be generated through neutral beam injection. In this study, we propose a model for calculating the radial electric field resulting from tangential local neutral beamlet injection, aiming to externally control and improve plasma confinement. The Neutral beamlet ion and Energetic particles Orbit mover and Electric field solver code has been developed to analyze this issue, and its simulation results have been validated against results from other codes as well as measurements from correlation reflectometers. The charge separation is primarily caused by the redistribution and loss of beam ions due to magnetic gradient and curvature drift as well as collision effects, and it is maintained through continuous beamlet injection. The electric field is calculated using Poisson’s equation, taking into account both classical and neoclassical polarization effects. The results demonstrate that despite the high losses and low heating efficiency associated with localized beamlets, they are capable of generating a significant radial electric field characterized by a steep gradient. This presents opportunities for external control of the electric field, potentially enhancing plasma confinement.

Longitudinal Development of Cosmic Noise Absorption Based on Multipoint Observations at Subauroral Latitudes During Storm‐Time Substorms on 25–28 August 2018

AbstractEnhancements in electron density in the D‐region ionosphere attributed to the precipitation of high‐energy electrons, have previously been inferred from increases in cosmic radio noise absorption (CNA) using ground‐based riometers. However, there have been few studies of CNA observations at multi‐point stations distributed in longitudes. Thus, the spatio‐temporal development of the global distribution of CNA is not well understood. In this study, we investigated the longitudinal extent of CNA using simultaneous riometer observations at six stations at subauroral latitudes in Canada, Alaska, Russia, and Iceland. These stations are located encircling the earth at ∼60° north magnetic latitudes. We have conducted simultaneous observations of CNA at these stations since October 2017. Here we focus on seven substorms during a geomagnetic storm 25–28 August 2018 and study the spatio‐temporal development of the global distribution of CNA during these substorms. For all seven substorms, some stations observed CNA enhancements after the substorm onsets. In five cases, the CNA enhancements started around midnight and expanded eastward. The other two cases show westward and anti‐sunward development of CNA. The eastward expansion of CNA indicates the eastward drift of high‐energy electrons, which is the source of the CNA, due to gradient and curvature drift in the geomagnetic field. The westward expansion of CNA may correspond to westward expansion of the substorm injection region due to dawn‐to‐dusk electric fields. These results indicate that spatio‐temporal development of CNA at subauroral latitudes corresponds to high energy electron drift in the inner magnetosphere.