Diamagnetic Drift Research Articles

Analytical solution to the problem of polarization drift compensation in all-fiber QKD system

Analytical solution to the problem of polarization drift compensation in all-fiber QKD system

Deposition of thin refractory-metal-films onto glasses through diaphragms at plasma focus facility

The results of experiments are presented on the deposition onto silicate glasses of thin refractorymetal- films: molybdenum, tantalum and tungsten. The technique used for manufacturing films was based on the deposition of metal-containing plasma formed when exposing the surface of foils made of refractory metals to high-power plasma and ion pulses. For generation of such pulses, the facility of plasma focus type was used, which makes it possible to obtain ion beams and plasma flows with the energy flux density in the range of 1010—1012 W/cm2. The most intense central part of the ion-plasma flow was separated using metal diaphragms with aperture diameters of 2.5, 3.5, and 4.5 mm. Metal Mo, Ta and W films with dimensions of ∅ 3—5 mm were obtained on the surfaces of glasses. Metal films are characterized by good adhesion, since they coalesce with the glass surface. It was discovered that the planarity of films becomes violated due to the drift of molten metal particles under the glass surface. The relief of films is non-uniform, which can be explained by the presence of micrometer-sized metal particles in the plasma flow.

Impurity convection reversal caused by edge localized turbulence for generating a stationary edge radiative layer in the HL-2A tokamak

Abstract Effect of impurity on edge turbulence was investigated on the HL-2A tokamak by using Neon supersonic molecular beam injection (SMBI). For the first time, a stationary radiative layer accompanied by edge localized turbulence lasting more than 100ms is observed at the edge region ρ=0.7-0.9. This duration is much longer than the SMBI pulse length (1.2ms), indicating that the impurity diffusion is on the whole cancelled out by the impurity convection without spreading of the localized turbulence during this period. This implies that the impurity convection is reversed from positive to negative impurity density gradient region. This reversal could be explained by the parallel impurity compression mechanism. The observed turbulence is a broadband electrostatic turbulence (25-70 kHz) propagating in the electron diamagnetic drift direction with normalized poloidal wavenumber of 0.1≤ kθρs≤0.4. It has been found that the excitation of the edge localized turbulence strongly depends on the local collisionality. This feature is qualitatively predicted by the spectral multiscale gyrokinetic turbulence simulation, which suggests that the turbulence could be a dissipative trapped electron mode (DTEM). This experiment demonstrates that mutual interaction between externally injected impurity ions and edge turbulence can generate a stationary edge radiative layer and avoid impurity core accumulation. These results could provide a potential approach for the formation of a stable impurity radiative layer by impurity injection in tokamaks.

Clock synchronization characterization of the Washington DC metropolitan quantum network (DC-QNet)

Quantum networking protocols relying on interference and precise time-of-flight measurements require high-precision clock synchronization. This study describes the design, implementation, and characterization of two optical time transfer methods in a metropolitan-scale quantum networking research testbed. With active electronic stabilization, sub-picosecond time deviation (TDEV) was achieved at integration times between 1 and 105 s over 53 km of deployed fiber. Over the same integration periods, 10-ps level TDEV was observed using the White Rabbit–Precision Time Protocol over 128 km. Measurement methods are described to understand the sources of environmental fluctuations on clock synchronization toward the development of in situ compensation methods. Path delay gradients, chromatic dispersion, polarization drift, and optical power variations all contributed to clock synchronization errors. The results from this study will inform future work in the development of compensation methods essential for enabling experimental research in developing practical quantum networking protocols.

A novel plasma source concept for negative ion generation in neutral beam injectors for fusion applications

Abstract A low-temperature plasma can very well be confined by a simple magnetic dipole, such as in the Van Allen belts of Earth’s magnetoshpere. This configuration can be reproduced in laboratory as a small experimental device, designed in such a way that the magnetic field lines remain within a vacuum-tight container and are virtually not intercepted by the container wall. In this paper we propose to use a dipole field for the realization of an efficient negative Ion source. To this purpose, we analyze the plasma confinement capabilities of such plasma source, in order to assess the equilibrium pressure and estimate the particle trajectories and drifts.

Effect of postemergence applications of aminocyclopyrachlor, aminopyralid, 2,4-D, and dicamba on non–auxin resistant soybean

Abstract Soybean [Glycine max (L.) Merr.] that lack resistance to auxin herbicides [i.e., not genetically modified for resistance] have well-documented responses to those particular herbicides, with yield loss being probable. When a soybean field is injured by auxin herbicides, regulatory authorities often collect a plant sample from that field. This research attempted to simulate soybean exposures due to accidental mixing of incorrect herbicides, tank contamination, or particle drift. This research examined whether analytical testing of herbicide residues on soybean to aminocyclopyrachlor (ACP), aminopyralid, 2,4-D, or dicamba would be related to the visual observations and yield responses from these herbicides. ACP and aminopyralid were applied to R1 soybean at 0.1, 1, and 10 g ae ha−1; 2,4-D and dicamba were applied at 1, 10, and 100 g ae ha−1. Visual evaluations and plant sample collections were undertaken at 1, 3, 7, 14, and 21 d after treatment (DAT), and yield was measured. The conservative limits of detection for the four herbicides in this project were 5, 10, 5, and 5 ng g−1 fresh weight of soybean for ACP, aminopyralid, 2,4-D, and dicamba, respectively. Many of the plant samples were non-detects, especially at lower application dosages. All herbicide concentrations rapidly declined soon after application, and many reached nondetectable limits by 14 DAT. All herbicide treatments caused soybean injury, although the response to 2,4-D was markedly lower than the responses to the other three herbicides. There was no apparent correlation between herbicide concentrations (which were declining over time) and the observed soybean injury (which was increasing over time or staying the same). This research indicated that plant samples should be collected as soon as possible after soybean exposure to auxin herbicides.

Universal fragmentation in annihilation reactions with constrained kinetics

In reaction-diffusion models of annihilation reactions in low dimensions, single-particle dynamics provides a bottleneck for reactions, leading to an anomalously slow approach to the empty state. Here, we construct a reaction model with a reciprocal bottleneck of reactions on particle dynamics in which single-particle motion conserves the center of mass. We show that such a constrained reaction-diffusion dynamics does not approach an empty state but freezes at late times in a state with fragmented particle clusters. The late-time dynamics and final density are universal, and we provide exact results for the final density in the large-reaction rate limit. Thus, our setup constitutes a minimal model for the fragmentation of a one-dimensional lattice into independent particle clusters. We suggest that the universal reaction dynamics could be observable in experiments with cold atoms or in the Auger recombination of exciton gases. Published by the American Physical Society 2024

Finite orbit width effects on turbulent transport of ion parallel momentum

Abstract A kinetic model for ion turbulent parallel momentum transport is developed with finite orbit width effects for Tokamak plasmas. It is shown that the curvature and gradient drifts of ions can introduce pressure perturbations into the transport equation of ion parallel momentum, which leads to a new source term. And the source term can be understood as a Coriolis force and can play a key role in the toroidal symmetry breaking during the spontaneous spin-up process.

Influence of the edge effect of the solenoid magnetic field on the discharge process of magnetron sputtering in long and narrow chambers

The fourth-generation light source or future particle accelerators have compact vacuum systems, resulting in a small flow conductance of the beam chamber. The development of NEG (Non-Evaporable Getters) films technology with distributed pumping is a good solution. This technology can obtain a pressure distribution with a small pressure gradient and an ultra-high vacuum of 10-8 Pa inside the vacuum chambers. In the magnetron sputtering process for NEG coating, the inhomogeneity of the magnetic field at the edge of the solenoid is a key parameter for affecting the stability of the magnetron sputtering discharge process. The influence mechanism of the edge magnetic field on the plasma discharge process and discharge uniformity was studied to optimize the coating parameters, which is very important. The Particle-In-Cell/Monte Carlo Collision (PIC/MCC) method was employed to simulate plasma discharge in a narrow vacuum chamber under various edge magnetic field conditions. The potential distribution, charged particle density distribution, and particle density distribution on the target were acquired for four sets of discharge parameters, followed by data processing and analysis. The electric field distribution during the discharge process is closely linked to the non-uniformity of the magnetic field at the solenoid's edge. The smaller Br (the radial component of the magnetic field) component of the magnetic field, the more uniform distribution of Ar+ on the target surface, and the smaller the difference along the length of the vacuum chamber. A smaller radial component (Br) of the magnetic field results in a more uniform distribution of Ar+ on the target surface and reduces variations in film thickness along the length of the vacuum chamber. This is attributed to the small distance between the inner wall of the vacuum chamber and the cathode target. The change in the edge magnetic field will result in the rapid migration of electrons to the inner wall of the vacuum chamber and insufficient collision with the discharge gas, making it challenging to sustain the discharge process. Moreover, fluctuations in the edge magnetic field of the solenoid induce gradient drift and curvature drift in charged particles, resulting in rapid electron loss and alterations in the density and potential distribution of charged particles at the ends of the vacuum chamber, ultimately leading to discharge instability. The research results show the importance of the edge magnetic field effect on the magnetron sputtering coating of the slender vacuum chambers, which provides an important reference for the segmented coating process of similar vacuum chambers in future accelerators.

Particle trajectories in the KP-II equation

In the current work, we consider particle trajectories beneath traveling soliton solutions described by the Kadomtsev–Petiviashvili-II (KP-II) equation, which is a model for small-amplitude water waves in shallow water. The KP-II equation has a large number of exact solutions describing crossing line solitons. Here, we describe the particle drift induced by the single line soliton and various two- and three-soliton solutions on a two-dimensional horizontal domain.First, the derivation of the KP-II equation is used to exhibit expressions for the three components of the fluid velocity vector induced by a surface wave profile given by the KP-II equation. These velocity components can be used to specify a coupled system of ordinary differential equations (ODEs) which describe the motion of a fluid particle. Given an initial position inside the fluid for a specific particle, as well as continuously providing time-dependent values for the surface deflection, the ODE system can be solved numerically to find the particle path induced by the passage of a wave. A special numerical integration grid tracking the particle is used to handle integral terms occurring in the fluid velocity expressions.

Comprehensive study of Kinetic Trajectory Simulation method for multi-component magnetized plasma-wall interaction process

For a wide range of plasma applications across diverse fields, a comprehensive understanding of the plasma-wall interaction mechanism is indispensable due to its inherent connection with confined plasma. This work compilation delves into the Kinetic Trajectory Simulation (KTS) method for the interaction of multi-component magnetized plasma with wall, specifically focusing on its implications for the tungsten wall sputtering model. In the evolution of the 1d3v (one dimensional spatial coordinates and three dimensional velocity coordinates) KTS method, the coupled set of kinetic equations has been solved under specified boundary conditions which yields results of higher accuracy. At the particle injection boundary, we have assumed the velocity distribution function of particle species to be cut-off Maxwellians, meeting essential requirements for plasma-wall transition processes: quasineutrality, sheath edge singularity, continuity of macroscopic fluid variables, and the kinetic Bohm sheath condition. The kinetic Bohm sheath condition, a fundamental criterion for plasma sheath formation, is extended for multi-component plasmas, accounting for the cut-off Maxwellian distribution of negatively charged particles. A comparative study of the kinetic Bohm sheath condition for cut-off and Boltzmann distributions reveals a deviation of less than 2.0% in magnitude. The concentration ratio of positive or negative ion species and the presheath side electron temperature influence various plasma-wall transition characteristics, including wall potential, Debye sheath thickness, particle densities, potential distribution, particle fluxes towards the surface, particle drift velocity, phase-space trajectory evolution, and physical sputtering of the tungsten surface. Although lighter ions possess higher energy when striking the surface, the physical sputtering yield of the tungsten surface is greater for heavier ions due to their lower threshold energy and larger collision cross-section. Furthermore, a comparative study of plasma-wall transition properties using kinetic and fluid approaches demonstrates qualitative similarities, with a notable deviation of approximately 4.0% in the magnitude in the vicinity of the material surface.

Investigation of electromagnetic fluctuations in a magnetically screened high beta plasma

We report low-frequency electromagnetic turbulence in large-volume plasma devices in a region that receives magnetically screened plasma. The magnetic screen is produced by the activation of a large solenoid that generates a strong magnetic field ( BEEF ) transverse to the background axial magnetic field ( Bz ). The magnetic field strength variation in BEEF controls the plasma diffusion and is responsible for parametric profile modifications in large volume plasma devices. The turbulence is characterized by the observed features of an electromagnetic mode having frequency ordering in the lower hybrid range (f ci < f < f LH). The free energy source for the excited turbulence is believed to be the prevalent finite radial pressure gradient in the system. The excited electromagnetic mode shows typical scales for the wave number, k⊥ ∼ 0.13 cm−1 and frequency f ∼ 6 kHz and propagates with phase velocity comparable to ion acoustic velocity, C s in electron diamagnetic drift direction. It is believed that the low-frequency pressure gradient-driven electromagnetic mode exhibits coupling with the lower hybrid or whistler wave.

Characteristics of Thin Magnetotail Current Sheet Plasmas at Lunar Distances

AbstractThe magnetotail current sheet plays a key role in the dynamics of Earth's magnetosphere. Specifically, the formation and subsequent reconnection of thin (ion‐gyroscale) current sheets are critical components of magnetospheric substorms. However, the precise mechanisms governing the configuration and distribution of current density in these thin current sheets remain elusive. By analyzing a data set consisting of 453 thin current sheet crossings observed by the Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) mission, we explore the statistical properties of the ion and electron pressures and current densities, Ji and Je, in the spacecraft rest frame. Using magnetotail flapping and magnetic field measurements to estimate the total current density, J0, we find that it agrees well with the sum of those from direct ion and electron measurements, Ji + Je, respectively. In 65% of thin current sheets, electrons were found to dominate the contribution to the total current density in the spacecraft frame, with a typical dawnward drift velocity of ≳100 km/s. Diamagnetic drifts of electrons and ions estimated from their respective vertical pressure profiles (along the current sheet normal) reveal that the gradient of electron pressure alone cannot fully account for the observed high values of Je/Ji. Counter‐intuitively, for most (52% of) thin current sheets the electron vertical pressure profile is wider than the ion pressure profile, again suggesting that electron diamagnetism is an insufficient contributor to the current density at such sheets. These findings suggest the presence of a significant E × B dawnward drift that the electrons can fully acquire but ions cannot, being partially unmagnetized. We compare our results with those previously reported for the near‐Earth magnetotail and discuss them in the context of magnetotail current sheet modeling.

Particle Acceleration in Relativistic Alfvénic Turbulence

Strong magnetically dominated Alfvénic turbulence is an efficient engine of nonthermal particle acceleration in a relativistic collisionless plasma. We argue that in the limit of strong magnetization, the type of energy distribution attained by accelerated particles depends on the relative strengths of turbulent fluctuations δ B 0 and the guide field B 0. If δ B 0 ≪ B 0, the particle magnetic moments are conserved, and the acceleration is provided by magnetic curvature drifts. Curvature acceleration energizes particles in the direction parallel to the magnetic field lines, resulting in log-normal tails of particle energy distribution functions. Conversely, if δ B 0 ≳ B 0, interactions of energetic particles with intense turbulent structures can scatter particles, creating a population with large pitch angles. In this case, magnetic mirror effects become important, and turbulent acceleration leads to power-law tails of the energy distribution functions.

Polar cap region and plasma drift in pulsars

ABSTRACT Pulsars often display systematic variations in the position and/or intensity of the subpulses, the components that comprise each single pulse. Although the drift of these subpulses was observed in the early years of pulsar research, and their potential for understanding the elusive emission mechanism was quickly recognized, there is still no consensus on the cause of the drift. We explore the electrodynamics of two recently proposed or refined drift models: one where plasma lags behind corotation, connecting the drift with the rotational pole; and another where plasma drifts around the electric potential extremum of the polar cap. Generally, these are different locations, resulting in different drift behaviours, that can be tested with observations. In this study, however, we specifically examine these models in the axisymmetric case, where the physics is well understood. This approach seems counter-intuitive as both models then predict similar large-scale plasma drift. However, it allows us to show, by studying conditions within the sparks for both models, that the lagging behind corotation model is inconsistent with Faraday’s law. The modified carousel (MC) model, where plasma drifts around the electric potential extremum, not only aligns with Faraday’s law, but also provides a future direction for developing a comprehensive model of plasma generation in the polar cap region. Unlike previous models, which considered the drift only inside the discharging regions, the MC model reveals that the electric field between the discharges is not completely screened, and plasma drifts there – a paradigm shift for the drifting subpulse phenomenon.

Northeast Arctic haddock (Melanogrammus aeglefinus) spawning grounds and drift to nursery areas in the Barents Sea

AbstractThe Northeast Arctic stock of haddock (Melanogrammus aeglefinus) is the most northerly stock of the species. It is one of the largest haddock stocks but not the most studied. Similar to the more extensively studied sympatric cod (Gadus morhua) and herring (Clupea harengus) stocks, it relies on Atlantic currents for egg and larvae transportation from spawning grounds to nursery areas in the Barents Sea. The exact locations of the spawning grounds have not been known and the maps that have been published differ substantially. Here, we present results from the first survey dedicated to exploring the spawning habitat of Northeast Arctic (NEA) haddock, and a particle drift and larvae growth model with physical forcing from a high‐resolution ocean model. Gadoid eggs, later identified as haddock by DNA analyses, as well as spawning individuals were sampled at the survey. Spawning haddock was found in Atlantic water in temperatures 3.6–6.2°C and depths of 240–560 m. Sampled eggs were mostly in early development stages, suggesting that they were largely spawned in the surveyed area. Using the drift model, we found that most of the modelled particles released as eggs at our surveyed area ended up in the nursery area in the Barents Sea. A crude estimate of the spawning stock biomass based on the survey suggests that the most updated spawning ground map of NEA haddock might be too restricted in its extent. Particle drift and growth with physical forcing for the years 2012–2022 indicated small interannual variation in aberrant drift, and that growth driven by ambient temperature could be important in explaining interannual variation in haddock recruitment.

High performance power handling in the absence of an H-mode edge in negative triangularity DIII-D plasmas

Experiments performed during strongly-shaped high-power diverted negative triangularity (NT) experiments in DIII-D achieved detached divertor conditions and a transient-free edge, showcasing the potential for application of NT to a core-edge integrated reactor-like scenario and providing the first characterization of the parametric dependencies for detachment onset. Detached divertor conditions will be required in future devices to mitigate divertor heat fluxes. Access to dissipative divertor conditions was investigated via an increase in upstream density. Detachment onset at the outer strike point was achieved with H-mode level confinement H98−y2∼1 and reactor-relevant normalized pressures βN∼2 . Confinement degradation was observed with deeper detachment, associated with the loss of an electron temperature pedestal. Differences in geometry, radial transport, impact of cross field drifts are discussed to explain differences in access to detachment in NT discharges. Higher normalized densities, with respect to equivalent discharges in positive triangularity, were necessary to achieve detachment, partially explained by the shorter parallel connection length to the targets. The effect of cross-field particle drifts (E×B, B ×∇ B) on access to detachment was demonstrated by the lower upstream density needed to access detachment with ion B ×∇ B drift directed outside of the active divertor (Greenwald fraction fGw∼ 0.9–1.0 vs fGw∼ 1.3). The upstream density at detachment onset was observed to increase linearly with plasma current with ion B ×∇ B drift into the divertor, consistent with the observed narrowing of the scrape-off layer heat flux width λ q . Edge fluid simulations capture separatrix densities needed to achieve detachment in NT plasma and their dependence on drift direction. The ability to reproduce detachment dynamics in NT plasma increases the confidence in future design studies for NT divertors.

The irreversibility of microscopic motions

People have long had a problem: the equations of motion that reflect the laws of physics are invariant under time inversion, while there always are irreversible processes for gases composed of microscopic particles. This article solves the problem. The point is that we should distinguish between the concepts of the equation of motion and concrete motion. We also need to distinguish between the concepts of time-inverse motion and reverse motion. The former is anticlockwise, which is a fictional motion, while the latter is clockwise. For the single-particle motions in classical mechanics and in quantum mechanics, we present mathematical expressions for time-inversion motion and reverse motion, respectively. We demonstrate that single-particle motion is irreversible. The definition of the reversibility of two-particle collisions is given. According to the definition, the two-particle collision as a microscopic motion process is irreversible. Consequently, for a gas consisting of a large number of particles colliding with each other, its movement should be irreversible, unless the condition of detailed balance is met. We provide a physical explanation for detailed balance, which does not concern the meaning of microscopic reversibility. The detailed balance means that after a pair of reciprocal collisions occur, the distribution function of the particles remains unchanged. Therefore, microscopic two-particle collision events are irreversible, but the statistical average of a large number of collision events makes it possible for the macroscopic process of a gas to be reversible. Conclusively, we clarify the microscopic mechanism of the irreversible process of gases.

Numerical simulation of dynamics behavior of pulsed-DC helium plasma jet confined by parallel magnetic field at atmospheric pressure

A two-dimensional axisymmetric fluid model is used to simulate the dynamics behavior of an atmospheric-pressure helium plasma jet in the presence of a parallel magnetic field. The plasma jet is generated in a coaxial dielectric barrier discharge (DBD) driven by pulsed direct-current voltage. Comparative analysis of the plasma jet with and without the parallel magnetic field indicates that a slightly thinner plasma sheath inside the tube is present with the parallel magnetic field as a result of the decreased accumulated electrons on the inner surface of dielectric tube. After the streamer propagates outside the tube, a little more concentrated electron distribution in the annular wall is observed by applying the magnetic field because of the reduced electron diffusion in the radial direction and the confinement effect of the magnetic field on the electrons in the avalanche heads. The tiny reduction in the length of plasma jet is attributed to the E × B drift of charged particles. These results demonstrate that the parallel magnetic field has no apparent effect on the propagation of the plasma jet, and it contributes little to the performance improvement of the coaxial DBD, which agrees well with the previous experimental observations. This little impact of the parallel magnetic field on the coaxial DBD plasma jet may result from negligible contribution of the memory effect to the sole discharge pulse as well as the weak confinement effect of the applied magnetic field on the surface electrons that moves along the magnetic field lines under electrostatic repulsion. Published by the American Physical Society 2024

Numerical modelling of sawteeth and sawtooth-free regime

To better understand the sawteeth physics and the sawtooth-free regime associated with the hybrid scenario in tokamak experiments, numerical calculations up to quasi-steady state have been carried out for realistic middle-size tokamak plasma parameters, including the bootstrap current perturbation and basing on both the single- and two-fluid equations with the large aspect ratio approximation. Two types of the sawtooth crash are found in multiple sawteeth simulations: (1) For a low equilibrium bootstrap current fraction, the crash is caused by the internal kink mode, as expected; (2) When the bootstrap current density fraction is larger than 10% in the core region, however, the crash is caused by the non-ideal double kink mode, in contrary to the conventional understanding. In this case, a non-monotonic radial profile of the safety factor q with two q=1 surfaces emerges before the crash, caused by the bootstrap current density and plasma resistivity perturbations, although the original equilibrium has only single q = 1 surface. In both types of sawtooth crashes, the crash time in two-fluid simulations is tens of microseconds, as observed in experiments. Furthermore, for a relatively low ion density and finite bootstrap current density fraction, a transition from the sawtooth to the sawtooth-free regime is found, in which flat q profiles with the q value being about unity in the central region, similar to that observed in hybrid scenario experiments, are maintained by the dynamo effect. To enter into the sawtooth-free regime in two-fluid simulations, a much larger Alfvén velocity than that in single-fluid simulations is required due to the diamagnetic drift.