Diamagnetic Drift Research Articles

A Pathway for Collisional Planetesimal Growth in the Ice-dominant Regions of Protoplanetary Disks

We present a semi-analytic model for the growth, drift, desorption, and fragmentation of millimeter- to meter-sized particles in protoplanetary disks. Fragmentation occurs where particle collision velocities exceed critical fragmentation velocities. Using this criterion, we produce fragmentation regions in disk orbital radius–particle size phase space for particles with a range of material properties, structures, and compositions (including SiO2, Mg2SiO4, H2O, CO2, and CO). For reasonable disk conditions, compact aggregate H2O, CO2, and CO ice particles do not reach destructive relative velocities and are thus not likely to undergo collisional fragmentation. Uncoated silicate particles are more susceptible to collisional destruction and are expected to fragment in the inner disk, consistent with previous work. We then calculate the growth, drift, and sublimation of small particles, initially located in the outer disk. We find that ice-coated particles can avoid fragmentation as they grow and drift inward under a substantial range of disk conditions, as long as the particles are aggregates composed of 0.1 μm-sized monomers. Such particles may undergo runaway growth in disk regions abundant in H2O or CO2 ice, depending on the assumed disk temperature structure. These results indicate that icy collisional growth to planetesimally relevant sizes may happen efficiently throughout a disk’s lifetime, and is particularly robust at early times when the disk’s dust-to-gas ratio is comparable to that of the interstellar medium.

The Hemispheric Difference in Electric Potential and Electron Precipitation Observed by DMSP in the Auroral Zone

AbstractIn this case study, we focus on how hemispheric differences in the electric potential distribution in the auroral zones are related to hemispheric differences in the energetic particle precipitation that indicate the presence of field‐aligned potential drops. Utilizing data during the spring and fall equinox in 2013 and 2014 from the Defense Meteorological Satellite Program (DMSP) F16 and F17 satellites, we systematically examine simultaneous measurements of plasma drift velocity and particle precipitation in magnetically conjugate regions across the auroral zone in both hemispheres. This allows us to establish the degree to which the interhemispheric differences in ionospheric electric potential may be accounted for by field‐aligned potential drops. Thirty‐seven eligible cases examined show accelerated electron energy spectra at conjugate locations in the northern and/or southern hemispheres. Of these 37 cases, 23 show conjugate differences in electric potential that agree qualitatively with the observed electron acceleration and average energy of precipitating electrons in each hemisphere. This result suggests that the hemispheric differences in ionospheric electric potential in the auroral zone may be most frequently accounted for by field‐aligned potential drops along the magnetic flux tubes connecting conjugate points to the equatorial plane. The spatial and temporal variability of the potential distribution, electron precipitation, and magnetic field configuration could account for deviations from the normally observed situation in the remaining cases. More magnetically conjugate observations at various altitudes in both hemispheres are needed to investigate this hemispheric coupling in more detail.

Unravelling the genetic pattern of seagrass (Posidonia oceanica) meadows in the Eastern Mediterranean Sea

AbstractThe genetic traits of seagrass populations are a crucial aspect of their ecology and evolution, influencing their adaptability and resilience. Here, we studied the genetic diversity, population structure, and connectivity of eighteen Posidonia oceanica meadows extending in the Eastern Mediterranean Sea (Aegean, Ionian and Cretan Seas, Greece), combining twelve microsatellite markers and Lagrangian particle drift modelling. Our findings revealed a strong genetic differentiation between the Ionian Sea and the Aegean and Cretan Seas, suggesting limited genetic exchange between these two groups. High gene flow was observed within the meadows of the Aegean and Cretan Seas, indicating a well-connected group of populations. Notably, populations of the North Aegean Sea displayed the lowest genetic diversity and the highest clonality compared to the rest of the populations. The lack of substantial oceanographic connectivity between Ionian and Aegean/Cretan Sea populations supported their genetic differentiation. However, the Lagrangian simulations did not fully support gene flow patterns in the Aegean Sea, suggesting that in addition to contemporary processes, historical events may have contributed to the formation of the observed genetic pattern. The genetic information provided here can be incorporated into management strategies aimed at identifying suitable areas as management units in conservation efforts and determining meadows that may serve as donor sites in transplantation initiatives.

F-region drift current and magnetic perturbation distribution by the X-wave heating ionosphere

Abstract. We present a theoretical and numerical study of the drift current and magnetic perturbation model in the ionosphere by incorporating the ohmic heating model and the magnetohydrodynamic (MHD) momentum equation. Based on these equations, the ionospheric electron temperature and drift current are investigated. The results indicate that the maximum change in electron temperature ΔTe is about 570 K, and the ratio is ΔTe/Te ∼ 48 %. The maximum drift current density is 8×10-10 A m−2, and its surface integral is 5.76 A. Diamagnetic drift current is the main form of current. The low collision frequency between charged particles and neutral particles has little effect on the current, and the collision frequency of electrons and ions is independent of the drift current. The current density profile is a flow ring. We present the effective conductivity as a function of the angle between the geomagnetic field and the radio wave; the model explains why the radiation efficiency was strongest when the X wave is heating along the magnetic dip angle, as reported in recent observations by Kotik et al. (2013). We calculate the magnetic field variation in the heating region based on the MHD theory: the results show that the maximum magnetic field perturbation in the heating area is 48 pT.

The effect of the diamagnetic drift on geodesic acoustic modes in tokamak plasmas

The effect of the radial derivative of the equilibrium particle distribution, i.e., the diamagnetic drift effect, on geodesic acoustic modes is taken into account in this work. The effect was routinely neglected in the previous studies on the geodesic acoustic mode since the dominant mode number is m/n=0/0. However, for finite electron temperatures, small m ≠ 0 side bands are present and the diamagnetic drift effect enters through these side bands. In this work, we find that the mode frequencies increase with the particle density gradient. The temperature ratio between electrons and ions, i.e., τ=Te/Ti, is a key parameter influencing this effect. The effect is more prominent for higher τ values. Another effect is the symmetry breaking of the propagating direction of the sideband potentials. In contrast to the pure standing wave form, the potential perturbation consists of a standing wave superimposed with a small amplitude traveling wave, which is nearly proportional to the density gradient.

The theory of kinetic effects on resistive wall mode stability in tokamaks

Tokamak fusion plasmas benefit from high pressures but are then susceptible to modes of instability. These magnetohydrodynamic (MHD) modes are macroscopic distortions of the plasma, but certain collective motions of individual particles can provide stabilizing effects opposing them. The presence of a resistive wall slows the mode growth, converting a kink to a resistive wall mode (RWM). A kinetic MHD model includes Maxwell's equations, ideal MHD constraints, and kinetic effects included through the pressure tensor, calculated with the perturbed drift-kinetic distribution function of the particles. The kinetic stabilizing effects on the RWM arise through resonances between the plasma rotation and particle drift motions: precession, bounce, and transit. A match between particle motions and the mode allows efficient transfer of energy that would otherwise drive the growth of the mode, thus damping the growth. The first approach to calculating RWM stability is to write a set of equations for the complex mode frequency in terms of known quantities and then to solve the system. The “energy principle” approach, which has the advantage of clarity in distinguishing the various stabilizing and destabilizing effects, is to change the force balance equation into an equation in terms of changes of kinetic and potential energies, and then to write a dispersion relation for the mode frequency in terms of those quantities. These methods have been used in various benchmarked codes to calculate kinetic effects on RWM stability. The theory has illuminated the important roles of plasma rotation, energetic particles, and collisions in RWM stability.

Observations of transient wave-induced mean drift profiles caused by virtual wave stresses in a two-layer system

An experimental study of long interfacial gravity waves was conducted in a closed wave tank containing two layers of viscous immiscible fluids. The study focuses on the development in time of the mean particle drift that occurs close to the interface where the two fluids meet. From a theoretical analysis by Weber & Christensen (Eur. J. Mech.-B/Fluids, vol. 77, 2019, pp. 162–170) it is predicted that the growing drift in this region is associated with the action of the virtual wave stress. This effect has not been explored experimentally before. Interfacial waves of different amplitudes and frequencies were produced by a D-shaped paddle. Particle tracking velocimetry was used to track the time development of the Lagrangian mean drift. The finite geometry of the wave tank causes a mean return flow that is resolved by mass transport considerations. The measurements clearly demonstrate the importance of the virtual wave stress mechanism in generating wave drift currents near the interface.

The effect of Jupiter on the CAI storage problem

Context. Meteorites preserve an imprint of conditions in the early Solar System. By studying the distribution of calcium-aluminium-rich inclusions (CAIs) that are embedded within meteorites, we can learn about the dynamical history of the protoplanetary disk from which our Solar System formed. A long-standing problem concerning CAIs is the CAI storage problem. CAIs are thought to have formed at high temperatures near the Sun, but they are primarily found in carbonaceous chondrites, which formed much further out, beyond the orbit of Jupiter. Additionally, radial drift of CAI particles should have removed them from the solar protoplanetary disk several million years before the parent bodies of meteorites in which they are encountered would have accreted. Aims. We revisit a previously suggested solution to the CAI storage problem by Desch, Kalyaan, and Alexander which proposed that CAIs were mixed radially outward through the disk and subsequently got trapped in a pressure maximum created by Jupiter’s growing core opening a planet gap. Our aim is to investigate whether their solution still works when we take into account the infall phase during which the disk builds up from the collapse of a molecular cloud core. Methods. We build a 1D numerical code in Python using the DISKLAB package to simulate the evolution of the solar protoplanetary disk, starting with a collapsing molecular cloud. CAIs are created in the model by thermal processing of solar nebula composition dust, and subsequently transported through the disk by turbulent diffusion, radial drift and advection by the gas. Results. We find that outward transport of CAIs during the infall phase is very efficient, possibly mixing them all the way into the far outer disk. Subsequent inward radial drift collects CAIs in the pressure maximum beyond Jupiter’s orbit while draining the inner disk, roughly reproducing parts of the result by Desch et al. By introducing CAI formation so early, abundances out to 100 AU remain significant, possibly not consistent with some meteoritic data. It is possible to create a disk that does not expand as far out and also does not push CAIs as far out by using a very slowly rotating cloud.

Observation of pedestal quasi-coherent mode in Type-I ELMy H-mode of HL-2A tokamak

High confinement mode plasma experiments with Type-I edge localized modes (ELMs) have been carried out on HL-2A tokamak. With neutral beam injection and lower hybrid current drive heating, a quasi-coherent mode (QCM) located at pedestal region has been observed, which exists during the ELM-free stage till the first ELM burst. Analysis based on density and magnetic fluctuations has revealed that the QCM propagating radially outward is electrostatic in nature whose radial wavenumber is kr∼0.5 cm−1 as well as the poloidal wavenumber around kθ∼1.4 cm−1, rotating in electron diamagnetic drift direction. The central frequency of the mode gradually decreases from 50 to 20 kHz, which varies almost linearly with toroidal rotation. Experimental findings indicate that the QCM is excited above a critical electron density gradient in the ELM-free phase during which the latter gradually increases due to the confinement transition. The disappearance of QCM is closely associated with the onset of ELMy H-mode, suggesting that the presence of QCM could potentially delay the occurrence of ELM bursts, consequently supporting the maintenance of an ELM-free operational regime. Moreover, the pedestal region locates more radially outside where the density gradient shows a more spanned region with QCM. A quantitative comparison between experimental measurements and linear GENE gyrokinetic simulations suggests that the dissipative trapped electron mode might be the candidate interpretation of the QCM.

The observation of avalanche-like transport during confinement power degradation in Heliotron J

In this study, we observe avalanche-like electron thermal transport in Heliotron J under plasma conditions that exhibit power degradation to the central electron cyclotron heating (ECH). The newly installed GHz sampling electron cyclotron emission diagnostic allows for the observation of the long-distance radial propagation of electron temperature fluctuations. We find that the electron temperature fluctuations are associated with avalanches, because the Te fluctuations (i) propagate from the core to the edge with a speed comparable to the diamagnetic drift velocity, (ii) exhibit a 1/f power-law scaling in the frequency spectrum and a Hurst exponent close to 1, and (iii) dominate in the ECH deposition location and spread to the edge as the heating power increases. Furthermore, the electron heat avalanches can spread to the scrape off layer region when they are enhanced, i.e., the Te fluctuations correlate with the Dα emission, which also has a frequency spectrum that scales with a 1/f power law.

Simulations of the Characteristics of the Entropy Mode in Dipole-Magnetic-Confined Plasmas.

Plasmas confined in a dipole magnetic field widely exist in both space and laboratories, and this kind of plasma draws much attention from researchers both in plasma physics and in space science. In this paper, the characteristics of the collisionless electrostatic instability of the entropy mode in a dipole-magnetic-confined plasma are simulated with the linear gyrokinetic model. It is found that the entropy mode can be generated in dipole-magnetic-confined plasmas, and there are two typical stages of the entropy mode, with another transitional stage at different values of η. The main instability changes from the ion diamagnetic drift to the electronic diamagnetic drift as η becomes larger. In addition, the MHD mode predicts that the most stable point is at η~2/3 when k⟂ρi << 1. However, we find that η and k⟂ρi are coupled with each other, and the most stable point of the mode moves gradually to η~1 as k⟂ρi increases. There is a peak value for the entropy mode growth rate around k⟂ρi~1.0, and more complicated modes are induced so that the dispersion relation has been changed when the driving force of the plasma pressure gradient effect is obvious. For example, the characteristics of the interchange-like modes gradually emerge when the driving effect of the plasma pressure becomes stronger. Further investigations should be taken to reveal the characteristics of the entropy mode in magnetospheric plasmas.

An improved random drift particle swarm optimization-feed forward backpropagation neural network for high-precision state-of-charge estimation of lithium-ion batteries

A predictive model with high accuracy and stability of the state of charge (SOC) estimation for lithium-ion batteries plays a significant role in electric vehicles. An improved random drift particle swarm optimization-feed forward backpropagation neural network (IRDPSO-FFBPNN) is established in this paper. Basically, a three-layer FFBPNN is established, and its learning process is analyzed in detail. Then, to avoid the particle out-of-control, inducting weight parameter σ to achieve dynamic control weight convergence. What's more, the cross-reorganization of data is proposed to enhance the utilization. Finally, a further performance comparison with other networks is made under different working conditions to prove the effectiveness of the IRDPSO-FFBPNN. The experimental results showed that the maximum SOC error of the IRDPSO-FFBPNN is 0.1021 % in 45 s, 0.1237 % in 116 s under BBDST and DST with different temperatures, respectively, which performed better both in terms of time-consumption and accuracy.

Trapped-particle precession and modes in quasisymmetric stellarators and tokamaks: a near-axis perspective

This paper presents the calculation of the bounce-averaged drift of trapped particles in a near-axis framework for axisymmetric and quasisymmetric magnetic fields that possess up-down and stellarator symmetry, respectively. This analytic consideration provides important insight on the dependence of the bounce-averaged drift on the geometry and stability properties of the field. In particular, we show that although the maximum- $\mathcal {J}$ property is unattainable in quasisymmetric stellarators, one may approach it through increased plasma $\beta$ and triangular shaping, albeit going through a reduced precession scenario with potentially higher particle losses. The description of trapped particles allows us to calculate the available energy of trapped electrons analytically in two asymptotic regimes, providing insight into the behaviour of this measure of turbulence. It is shown that the available energy is intimately related to magnetohydrodynamics (MHD) stability, providing a potential synergy between this measure of gyrokinetic turbulence and MHD stability.

Cross phases of temperature-gradient-driven turbulence as a model basis for I-mode particle transport

As a model for understanding the type of transport behavior characteristic of the tokamak I mode, cross-phase physics for particle-transport is studied analytically for turbulence dominated by either ion-temperature-gradient (ITG) or electron-temperature-gradient (ETG) instability. I mode is a transport-barrier regime of reduced thermal transport but essentially unaffected particle transport. It is assumed that ITG turbulence applies to the baseline L mode, ETG to I mode, and that E × B flow shear is stronger in I mode, lowering all fluxes. In ITG turbulence, particle transport is governed by trapped electrons. Sensitivity to collisions produces the well-known temperature-gradient-driven pinch that offsets density-gradient-driven outward diffusion, weakening particle transport in L mode. In ETG turbulence, nonadiabatic ions are collisionless. Nonzero transport requires an ion spectrum feature whose magnetic-drift resonance supplies the necessary cross phase. If frequencies of order the ion diamagnetic drift frequency dominate the ion part of the spectrum, as would occur with weakly unstable ITG turbulence, all components of the particle transport are outward and can offset flow-shear-induced flux reductions to produce a flux that is similar to the ITG L-mode particle flux. Nonlinear frequencies are potentially relevant and discussed in relation to I mode.

On irregularities in the cosmic ray spectrum of \(10^{16}-10^{18}\) eV range

Existing small, medium and large arrays for the study of cosmic rays of ultra-high energies are aimed for obtaining information about our galaxy and extragalactic space, namely to search and study astronomical objects that produce the flux of relativistic particles. The drift and interaction of such particles with magnetic fields and shock waves taking place in interstellar space causes the same interest. The shape of the energy spectrum of cosmic rays in the energy range 10^{15}-10^{18}1015−1018 eV, where the "knee" and the "second knee’’ are observed, can be formed as a superposition of the partial spectra of various chemical elements. Verification of galactic models, using recent experimental spectral data, makes it possible to study the nature of the galactic and extragalactic components of cosmic rays. The paper presents the result of the energy spectrum of cosmic rays in the range 10^{16}-10^{18}1016−1018 eV of measurements obtained with the Small Cherenkov array - a part of the Yakutsk array.

Gas puff imaging measurements during resonant magnetic perturbations on the HL-2A tokamak

The gas puff imaging diagnostic is used for the investigation of the poloidal flow and turbulent fluctuations at the plasma edge and scrape-off layer (SOL) on the HL-2A tokamak. The impact of resonant magnetic perturbations (RMPs) on the edge poloidal velocity ( Vθ ) are investigated and compared during the operation of a stair-like rising RMP coil current ( IRMP ). The application of the RMP is observed to modify the poloidal velocity significantly. When IRMP exceeds 4 kA, the turbulence poloidal velocity at the edge changes direction from electron to ion diamagnetic drift. This phenomenon is explained by the electron loss along the perturbed radial magnetic field (Br) with RMP, with the experimental evidence provided that the edge electric potential increases significantly. A strong impact of the RMP on the properties of plasma density fluctuations in the SOL is also observed. With RMP, both skewness and kurtosis are smaller in the SOL and large-scale turbulence structures (small kr and kθ ) are suppressed in both edge and SOL. These results can improve our understanding of the interaction between RMP and edge turbulence and in particular, the edge poloidal flow.

Rotational and translational drags of a Janus particle close to a wall and a lipid membrane

HypothesisMeasuring rotational and translational Brownian motion of single spherical particles reveals dissipations due to the interaction between the particle and the environment. ExperimentsIn this article, we show experiments where the in-plane translational and the two rotational drag coefficients of a single spherical Brownian particle can be measured. These particle drags are functions of the particle size and of the particle–wall distance, and of the viscous dissipations at play. We measure drag coefficients for Janus particles close to a solid wall and close to a lipid bilayer membrane. FindingsFor a particle close to a wall, we show that according to hydrodynamic models, particle–wall distance and particle size can be determined. For a particle partially wrapped by lipid membranes, in absence of strong binding interactions, translational and rotational drags are significantly larger than the ones of non-wrapped particles. Beside the effect of the membrane viscosity, we show that dissipations in the deformed membrane cap region strongly contribute to the drag coefficients.

Cold damping of levitated optically coupled nanoparticles

Methods for controlling the motion of single particles, optically levitated in vacuum, have developed rapidly in recent years. The technique of cold damping makes use of feedback-controlled, electrostatic forces to increase dissipation without introducing additional thermal fluctuations. This process has been instrumental in the ground-state cooling of individual electrically charged nanoparticles. Here we show that the same method can be applied to a pair of nanoparticles, coupled by optical binding forces. These optical binding forces are about three orders of magnitude stronger than typical Coulombic inter-particle force and result in a coupled motion of both nanoparticles characterized by a pair of normal modes. We demonstrate cold damping of these normal modes, either independently or simultaneously, to sub-Kelvin temperatures at pressures of 5×10−3mbar. Experimental observations are captured by a theoretical model that we use to survey the parameter space more widely and to quantify the limits imposed by measurement noise and time delays. Our work paves the way for the study of quantum interactions between meso-scale particles and the exploration of multiparticle entanglement in levitated optomechanical systems.

Tokamak plasma equilibrium with relativistic runaway electrons

We consider axisymmetric equilibrium of a tokamak plasma that includes current carried by relativistic runaway electrons (REs). Using a guiding center approach, a qualitative picture of the equilibrium of a pure RE beam is elucidated. In a hot thermal plasma, none of the classical drifts of charged particles contribute to the net field-perpendicular current density, which is purely due to magnetization current. In the case of a runaway beam, however, the curvature drift of REs provides the Lorentz force needed to maintain the centripetal acceleration associated with the relativistic toroidal motion. Two different equilibrium formulations are derived for the general case consisting of a mix of thermal and RE current. At higher RE energies, the shift between flux-surfaces and surfaces of constant generalized angular momentum of REs in such equilibria can exceed the radial extent of a typical magnetohydrodynamic mode such that its stability properties could be altered. Simplified one-dimensional governing equations are derived for the absolute and relative orbit shifts in the case of a circular tokamak, enabling quick estimates of parameter dependencies.

Continuous-variable quantum key distribution with time-division dual-quadrature homodyne detection.

We propose a novel heterodyne detection scheme for continuous-variable quantum key distribution (CVQKD), which measures both quadrature components of a quantum signal encoded in optical phase space. The proposed method uses time division to achieve identical performance to conventional heterodyne detection with only a single homodyne detection system. Our method also uses a Faraday-Michelson interferometer to make it independent of polarization drift and eliminate the need for dynamic polarization control. Our method is experimentally demonstrated using the Gaussian-modulated coherent-states (GMCS) protocol over a 20.06 km optical fiber channel, achieving an expected secret key rate of up to 0.187 Mbps.