Azimuthal Motion Research Articles

Electron trapping efficiency of a magnetron sputtering cathode

A common feature of all types of magnetron sputtering (MS) assemblies is an effective confinement of electrons by an appropriate combination of electric and magnetic fields. Therefore, studying the motions of electrons in the fields of magnetron assemblies is of particular importance. Here, we systematically analyze the electrons motions in front of a typical DC MS cathode. We first calculate the profiles of the magnetron’s magnetic field for balanced and two types of unbalanced configurations. Then, we compute the profiles of the cathode’s electric field before the gas discharge and after the plasma formation. A semi-analytical model is utilized to compute the plasma potential. We then track the motions of electrons released from the target and electrons produced through impact ionization of the background gas in the prescribed fields. A Monte Carlo model is implemented to consider electron-gas collisions and a mixed boundary condition is employed to account for electron-wall interactions. The study analyzes the impact of field profiles on the cathode’s efficiency in trapping electron by examining electron escape from the magnetic trap and electron recapture at the target surface. It is shown that the presence of plasma in all configurations leads to a significant increase in the trapping efficiency and the ionization performance, as well as a decrease in the recapture probability. These effects are attributed to the high electric field developed in the cathode sheath. Moreover, we statistically analyze the trapping efficiency by illustrating the spatial distributions of electrons locations in both axial and radial dimensions. It is demonstrated that during their azimuthal drift motion, the electrons released from the middle region at the target surface have the smallest range of axial and radial locations, in all configurations in the absence of plasma. Finally, the impact of field profiles on the average energies of electrons is discussed.

The Mass of the Large Magellanic Cloud from the Three-dimensional Kinematics of Its Globular Clusters

We estimate the mass of the Large Magellanic Cloud (LMC) using the kinematics of 30 LMC globular clusters (GCs). We combine proper motions measured with the Hubble Space Telescope, Gaia, or a combination of the two, from a recent study by Bennet et al. with literature line-of-sight velocities (LOSVs) to give three components of motion. With these, we derive a 3D velocity dispersion anisotropy β=−0.72−1.07+0.62 , consistent with the GCs forming a flattened system with significant azimuthal motion. We then apply a tracer mass estimator and measure an enclosed mass M(<13.2kpc)=2.66−0.36+0.42×1010 M ⊙. This is broadly consistent with results from previous studies of the LOSVs of GCs and other luminous tracers. Assuming a cosmologically constrained Navarro–Frenk–White distribution for the dark matter, this implies a virial mass Mvirial=1.80−0.54+1.05×1011 M ⊙. Despite being an extrapolation by almost an order of magnitude in radius, this result is consistent with published estimates from other methods that are directly sensitive to the LMC’s total mass. Our results support the conclusion that the LMC is approximately 17−6+10 % of the Milky Way’s mass, making it a significant contributor to the Local Group potential.

Trivelpiece–Gould modes and low-frequency electron–ion instability of non-neutral plasma

The frequency spectra of the Trivelpiece–Gould modes of a waveguide partially filled with non-neutral plasma are determined numerically by solving the dispersion equation. The modes having azimuthal number $m = 1$ are considered. The results are presented for the entire acceptable range of electron densities, magnetic field strengths, for different values of the charge neutralization coefficient. The Cherenkov resonance condition of an ion with a diocotron mode having a finite value of the longitudinal wave vector was studied. The characteristics of resonant low-frequency electron–ion instability caused by relative azimuth motion of electrons and ions in crossed fields and by the anisotropy of the distribution function of ions are discussed. Ions are created by ionization of residual gas in the plasma volume. Due to the anisotropy, instability occurs not only in the vicinity of the resonance, but also outside it. For typical values of plasma parameters in experiments, estimations of the frequency growth rate are given. A conclusion is drawn that this instability can be the cause of the low-frequency oscillations observed in linear devices with non-neutral plasma produced in an electron beam channel.

Space weather with an arc’s ∼2 h trip across the nightside polar cap

Flow channels can extend across the polar cap from the dayside to the nightside auroral oval, where they lead to localized reconnection and auroral oval disturbances. Such flow channels can persist within the polar cap &amp;gt;1½ hours, can move azimuthally with direction controlled by IMF By, and may affect time and location of auroral oval disturbances. We have followed a polar cap arc as it moved duskward from Canada to Alaska for ∼2 h while connected to the oval. Two-dimensional ionospheric flows show an adjacent flow channel that moved westward with the arc and was a distinct feature of polar cap convection that locally impinged upon the outer boundary of the auroral oval. The flow channel’s interaction with the oval appears to have triggered two separate substorms during its trip across western Canada and Alaska, controlling the onset location and contributing to subsequent development of substorm activity within the oval. The first substorm (over Canada) occurred during approximately equatorward polar cap flow, whereas the second substorm (over Alaska) occurred as the polar cap arc and flow channel bent strongly azimuthally and appeared to “lay down” along the poleward boundary. The oval became unusually thin, leading to near contact between the polar cap arc and the brightening onset auroral arc within the oval. These observations illustrate the crucial role of polar cap flow channels in the time, location, and duration of space weather activity, and the importance of the duration and azimuthal motion of flow channels within the nightside polar cap.

Reversal of drift direction during the Laschamp geomagnetic excursion

Earth's magnetic field changes in both space and time: the temporal changes are called geomagnetic and paleomagnetic secular variations. Westward drift has been noted as a feature of secular variation for several centuries, but eastward drift has received less attention. We use three global geomagnetic field models covering the past 100 kyr to extend temporal coverage for tracking the zonal (azimuthal) motion of the radial magnetic field. The models we use are GGF100k (100–0 ka), GGFSS70 (70–15 ka), LSMOD.2 (50–30 ka); the extent of the models enables the inclusion of the extreme secular variations found during excursions, particularly the Laschamp excursion (42–40 ka). GGFSS70 and LSMOD.2 have higher temporal resolution than GGF100k, but their underlying data have poorer spatial coverage. Spatial structure is greatly diminished in all models for spherical harmonic degrees l>4.We use two types of time-longitude plots, one of the full radial field to expose reverse and intense flux patches at the core-mantle boundary. The second time-longitude plot is processed to enhance zonal motion signatures and allows us to use Radon drift analyses to uncover characteristic time scales of both westward and eastward drift at mid to high latitudes in both the northern and southern hemispheres. Our results differ across the three models, which we attribute to varying degrees of resolution, accuracy, and data distribution. Nevertheless, recurrent episodes of both eastward and westward drift ranging from ±0.05o/yr to ±0.18o/yr occur in both the northern and southern hemispheres. Westward drift dominates. We also observe 8–20 kyr intervals between occurrences of high-latitude reverse flux patches correlated with strong drift signals. Focusing on the period 50–30 ka, we observe dominant eastward drift preceding the Laschamp excursion and westward drift subsequently. In a period not associated with an excursion, 90–80 ka, we see strong mid to high latitude drift signatures in the northern hemisphere.

The role of magnetic waves in tangent cylinder convection

The secular variation of the geomagnetic field suggests that there are anticyclonic polar vortices in the Earth's core. Under the influence of a magnetic field, the polar azimuthal flow is thought to be produced by one or more coherent upwellings within the tangent cylinder, offset from the rotation axis. In this study, convection within the tangent cylinder in rapidly rotating dynamos is investigated through the analysis of forced magnetic waves. The first part of the study investigates the evolution of an isolated buoyancy disturbance in an unstably stratified rotating fluid subjected to an axial magnetic field. It is shown that the axial flow intensity of the slow Magnetic-Archimedean-Coriolis (MAC) waves becomes comparable to that of the fast MAC waves when |ωM/ωC|∼0.1, where ωM and ωC are the Alfvén wave and inertial wave frequencies respectively. In spherical shell dynamo simulations, the isolated upwellings within the tangent cylinder are shown to originate from the localized excitation of slow MAC waves in the dipole-dominated regime. Axial flow measurements in turn reveal the approximate parity between the slow and fast wave intensities in this regime, which corresponds to the existence of strong polar vortices in the Earth's core. To obtain the observed peak azimuthal motions of 0.6–0.9∘yr−1, the Rayleigh number in the low-inertia geodynamo must be ∼103 times the Rayleigh number for the onset of nonmagnetic convection. However, if the forcing is so strong as to cause polarity reversals, the field within the tangent cylinder decays away, and the convection takes the form of an ensemble of plumes supported entirely by the fast waves of frequency ω∼ωC. The resulting weak polar circulation is comparable to that obtained in nonmagnetic convection.

First exploratory survey of poloidal magnetic flux emission from a dense plasma focus

Studies of neutron emission from a dense plasma focus suggest that a significant fraction of neutron emission in some shots is caused by fast deuterons that have a prominent azimuthal component of motion. Recent examples are observations of long-lasting neutron emission in the side-on direction in PF-1000 and of neutron flux asymmetry (end/side) less than unity in Gemini. Such azimuthal motion of deuterons indicates the presence of an azimuthal electric field that accelerates them and a poloidal magnetic field that keeps them within the zone of acceleration. This in turn must be accompanied by poloidal magnetic flux emission (PMFE) from the plasma focus. Recently, a diagnostic technique for detection of PMFE has been proposed and demonstrated. This paper presents results of its successful replication and the first ever exploratory survey of PMFE emission using the UNU-ICTP plasma focus at the Nanyang Technological University, Singapore.

The effect of the cell tilting on the temperature oscillation in turbulent Rayleigh–Bénard convection

We experimentally studied the effect of cell tilting on the temperature oscillation in turbulent Rayleigh–Bénard convection. We simultaneously measured the temperature using both in-fluid and in-wall thermistors for Ra=1.7×109 and 5.0×109 at Prandtl number Pr = 5.3. The tilt angles relative to gravity are set to 0°, 0.5°, 1°, 2°, and 7°. It is found that the temperature oscillation intensity measured in-fluid is much stronger than that measured in-wall, because the in-fluid thermistors measure both the large-scale circulation (LSC) and the plumes/plume clusters, while the in-wall thermistors only measure the LSC due to the filter effect of the sidewall. Despite the intensity difference, the obtained azimuthal profiles of the oscillation intensity measured by in-fluid and in-wall share similar spatial distribution, and the spatial distribution can be explained by the torsional motion near the top and bottom plates and the sloshing motion at the mid-height. With the in-fluid measurements, we find that with the increase in the tilt angle, the azimuthal profile of oscillation evolves toward a sawtooth-like profile and the intensity gets more prominent, which implies that the temperature oscillation becomes more coherent. Through a conditional sampling method based on the azimuthal position of LSC, we reveal that the uniformly distributed oscillation intensity in the level cell is the result of the superimposition of the random azimuthal motion and the sloshing motion. Tilting the cell can efficiently disentangle the above-mentioned two types of motions of LSC. Moreover, we found that the frequency of the temperature oscillation increases when the tilt angle increases, while the amplitude of the sloshing motion of the LSC remains unchanged, which is believed to be related to the confinement of the convection cell.

On the Evolution of Tropopause Layer Cooling Over Tropical Cyclone

AbstractThis study investigates the evolution of tropopause layer cooling (TLC) in an idealized tropical cyclone (TC) as well as the physical mechanism for its formation throughout its lifetime. TLC development is closely related to the intensity change of the TC. The TLC within the inner core of a TC coincides with the occurrence of the TC warm core, whereas the enhancement of the TLC precedes the strengthening of the warm core and the intensification of the TC. This phenomenon suggests that the TLC could be a valuable signal for predicting TC intensity and intensity change. After the onset of rapid intensification, the TLC continues to enhance until it is replaced by the warm core in the inner core region, and it expands to the outer core area and forms a cold ring above the TC outflow layer. The budget analyses of the azimuthal mean potential temperature indicate that advection plays a leading role during all stages of the TLC evolution. Prior to and during the rapid intensification stages of a TC, advection (due to eddy motion) contributes to a cooling of the upper layer above the TC center. This upper‐level cooling is assumed to be related to the uplift caused by overshooting and convection within the inner core. However, the advection process caused by the azimuthal vertical motion dominated the broad cooling across the whole TLC area.

TRIVELPIECE-GOULD MODES OF WAVEGUIDE PARTIALLY FILLED WITH NON-NEUTRAL PLASMA. PART 3

The possibility of explaining the nature of low-frequency oscillations observed in devices with non-neutral plasma by the instability of the relative azimuth motion of non-neutral plasma components and by anisotropy of the ion distribution function is discussed. The resonance condition for ions with a diocotron mode with a finite value of the longitudinal wave vector kz is studied. Numerical estimations are made for the plasma parameters and unstable oscillations, that are characteristic for experiments. Frequencies, growth rates, and other characteristics and features of the expected electron-ion instability are estimated. The conclusion is made that the nature of low-frequency oscillations observed in devices with non-neutral plasma can be explained by this instability.

Motion of a Light Free Sphere and Liquid in a Rotating Vertical Cylinder of Finite Length

The paper is devoted to an experimental study of the fluid motion excited by a light spherical body floating along the axis of a rotating vertical cylinder. The experiments are performed with fast rotation. The high-speed video recording examines the behavior of the body depending on the rotation rate and liquid viscosity. PIV-method is used to investigate the velocity fields of liquid. In the cavity frame, the body excites the motion liquid in the form of a Taylor–Proudman column, the diameter of which is consistent with the body diameter. In the upper column, the liquid performs a retrograde differential rotation, and in the lower, a prograde one. Outside the columns, the differential rotation is practically absent. It is found that the intensity of the retrograde azimuthal motion in the frontal column increases as the body goes up, while the intensity of the prograde rotation in the rear column decreases. As a result, the free body simultaneously with motion along the axis performs differential rotation: in the lower part of the cavity it is prograde, while in the upper one it is retrograde. The intensity of the body differential rotation varies with the longitudinal coordinate linearly and decreases with the dimensionless rotation velocity.

Nonlinear Evolution of Streaming Instabilities in Accreting Protoplanetary Disks

The streaming instability (SI) is one of the most promising candidates for triggering planetesimal formation by producing dense dust clumps that undergo gravitational collapse. Understanding how the SI operates in realistic protoplanetary disks (PPDs) is therefore crucial to assess the efficiency of planetesimal formation. Modern models of PPDs show that large-scale magnetic torques or winds can drive laminar gas accretion near the disk midplane. In a previous study, we identified a new linear dust-gas instability, the azimuthal drift SI (AdSI), applicable to such accreting disks and is powered by the relative azimuthal motion between dust and gas that results from the gas being torqued. In this work, we present the first nonlinear simulations of the AdSI. We show that it can destabilize an accreting, dusty disk even in the absence of a global radial pressure gradient, which is unlike the classic SI. We find the AdSI drives turbulence and the formation of vertically extended dust filaments that undergo merging. In dust-rich disks, merged AdSI filaments reach maximum dust-to-gas ratios exceeding 100. Moreover, we find that even in dust-poor disks the AdSI can increase local dust densities by 2 orders of magnitude. We discuss the possible role of the AdSI in planetesimal formation, especially in regions of an accreting PPD with vanishing radial pressure gradients.

Azimuthal Motion of Poleward Moving Auroral Forms

AbstractPoleward moving auroral forms (PMAFs), the most common dayside auroral structure, images the process of energy and particle transport from the solar wind to the magnetosphere via magnetic reconnection. This form of aurora moves not only poleward, but also in the azimuthal (dawn‐dusk) direction. However, the underlying mechanism responsible for the azimuthal motion of PMAFs are not thoroughly investigated. Here based on all‐sky imager observations in the southern hemisphere, we statistically determine that the azimuthal motion of PMAFs is highly dependent on the dawn‐dusk component of the interplanetary magnetic field (IMF By). Using three‐dimensional (3‐D) global hybrid simulations, we demonstrate that IMF By controls the azimuthal motion of PMAFs through plasma flow derived from magnetic tension of magnetopause flux ropes. Our study, by focusing on the azimuthal motion of PMAFs, allows a better understanding of space weather, especially from a 3‐D perspective.

Radial velocities from far-red spectra of Carina Arm O and early B stars

ABSTRACT Massive O and early B stars are important markers of recent star formation and exert a significant influence on their environments during their short lives via photoionization and winds and when they explode as supernovae. In the Milky Way, they can be detected at great distances but often lie behind large dust columns, making detection at short wavelengths difficult. In this study, the use of the less extinguished far-red spectrum (8400–8800 Å) for radial velocity measurement is examined. Results are reported for a sample of 164 confirmed OB stars within a 2° field positioned on the Carina Arm. Most stars are at distances between 3 and 6 kpc, and Westerlund 2 is at the field edge. The measured radial velocities have errors concentrated in the 3–10 km s−1 range, with a systematic uncertainty of 2–3 km s−1. These are combined with Gaia-mission astrometry to allow full space motions to be constructed. Up to 22 stars are likely to be runaways, although 8 of them are as likely to be interloping (so far undetected) binaries. The mean azimuthal motion of the sample fits in with recent measurements of Galactic disc rotation. In the Galactocentric radial direction, the mean motion indicates modest infall at a speed of ∼10 km s−1. This experiment shows that weak Paschen lines in the far-red can yield credible radial velocity determination, offering the prospect of exploring OB-star kinematics over much more of the Galactic disc than has hitherto been possible.

Constraining black-hole binary spin precession and nutation with sequential prior conditioning

We investigate the detectability of subdominant spin effects in merging black-hole binaries using current gravitational-wave data. Using a phenomenological model that separates the spin dynamics into precession (azimuthal motion) and nutation (polar motion), we present constraints on the resulting amplitudes and frequencies. We also explore current constraints on the spin morphologies, indicating if binaries are trapped near spin-orbit resonances. We dissect such weak effects from the signals using a sequential prior conditioning approach, where parameters are progressively re-sampled from their posterior distribution. This allows us to investigate whether the data contain additional information beyond what is already provided by quantities that are better measured, namely the masses and the effective spin. For the current catalog of events, we find no significant measurements of weak spin effects such as nutation and spin-orbit locking. We synthesize a source with a high nutational amplitude and show that near-future detections will allow us to place powerful constraints, hinting that we may be at the cusp of detecting spin nutations in gravitational-wave data.

Darcy-Forchheimer flow behavior and thermal inferences with SWCNT/MWCNT suspensions due to shrinking rotating disk*

The goal of the present investigation is to explore the flow and thermal behavior of non-Newtonian fluid with single-walled carbon nanotube (SWCNT)/multi-walled carbon nanotube (MWCNT) suspensions over a shrunk rotating disk subject to Darcy-Forchheimer effect. The mechanisms of suction, viscous dissipation and thermal radiation have been implemented. Entropy generation analysis is carried on. Innovated Nayak-Shaw number is modeled and its profiles analysis are narrated in a lucid manner. Noble bv4c method cum shooting technique is instrumental to devise a requisite numerical solution of the developed system of the dimension-free boundary layer equations. The outcomes of the study include amplification of non-Newtonian parameter (Casson parameter) that controls the radial and azimuthal motions. Inclusion of a significant interfacial nanolayer upgrades the heat transfer rate that in turn provides better cooling for industrial needs. Addition of more nanoparticles and a medium with high porosity (Darcy-Forchheimer effect) contribute to the entropy minimization which is ubiquitous for the greater efficiency of specific thermal systems. Nayak-Shaw number due to the fluid friction irreversibility peters out and that due to porous medium irreversibility ameliorates with the strengthening of porosity parameter effectively. It is obvious that the contribution of porous medium irreversibility dominates over due to fluid friction irreversibility.

Pattern formation on the surface of the granular medium in a horizontal rotating cylinder filled with fluid

We observe a new type of pattern formation at the interface between fluid and heavy granular medium in a horizontal rotating cylinder. Gravitational force perturbs the surface of the granular medium and induces azimuthal motion of suspended granules relative to the rotating fluid. The analysis of the experimental data shows that the length of the observed ripples is consistent with the predictions of the theory of the Kelvin-Helmholtz instability.

Optimal design and trajectory tracking experiment of a novel 3-DOF parallel antenna mechanism

The tracking range and pointing performance of the antenna are important indices to measure the antenna system. First, the 3 degree of freedom parallel mechanism is proposed for the supporting mechanism of the antenna. The trajectory tracking principle of the antenna mechanism is analyzed based on the inverse position solution model. Meanwhile, the kinematic model of the antenna mechanism with a specific motion trajectory is derived. In addition, the structural optimization design is demonstrated based on the actuation torques and motion range index. In addition, the trajectory planning research is carried out according to the trajectory tracking requirements. The trajectory planning simulation is carried out in the joint space. Afterward, the antenna motion range is obtained through simulation. The specific trajectory tracking simulation of the antenna is completed. Furthermore, the pitch and azimuth motion performance experiments are carried out based on the developed antenna mechanism prototype. Finally, the pentagram trajectory tracking performance is verified via experiments. This research serves as a reference for designing and engineering application of the antenna.

Classification of radial Kerr geodesic motion

We classify radial timelike geodesic motion of the exterior non-extremal Kerr spacetime by performing a taxonomy of inequivalent root structures of the first order radial geodesic equation using a novel compact notation and by implementing the constraints from polar, time and azimuthal motion. Four generic root structures with only simple roots give rise to eight non-generic root structures when either one root becomes coincident with the horizon, one root vanishes or two roots becomes coincident. We derive the explicit phase space of all such root systems in the basis of energy, angular momentum and Carter's constant and classify whether each corresponding radial geodesic motion is allowed or disallowed from existence of polar, time and azimuthal motion. The classification of radial motion within the ergoregion for both positive and negative energies leads to 6 distinguished values of the Kerr angular momentum. The classification of null radial motion and near-horizon extremal Kerr radial motion are obtained as limiting cases and compared with the literature. We explicitly parametrize the separatrix describing root systems with double roots as the union of the following three regions that are described by the same quartic respectively obtained when (1) the pericenter of bound motion becomes a double root; (2) the eccentricity of bound motion becomes zero; (3) the turning point of unbound motion becomes a double root.

MHD vortex flow in liquid metal near a spherical particle with different conductivity

The flow of a liquid metal near a spherical particle, whose electrical conductivity differs from that of the liquid metal, is considered. A cylindrical vessel with metal is in an axial magnetic field and, accordingly, with an axial electric current flowing through it. If the conductivity of the particle is equal to the conductivity of the liquid, then the electric current flows along the magnetic field lines and there are no electromagnetic forces in the system. In the case of different conductivity, the electric field lines are either drawn to the particle or go around it, which causes the appearance of electromagnetic forces that generate a vortex flow of the metal. The flow consists of two toroidal vortices, in which the azimuthal motion develops in opposite directions. The poloidal flow in both vortices is arranged in such a way that the liquid on the axis of the cylinder always moves towards the particle. It is shown that the flow energy rapidly increases when the particle conductivity deviates from the liquid conductivity, and reaches asymptotes when the difference in conductivities turns out to be significant. So, with a relative difference in conductivity of only one percent, the energy of the azimuthal flow reaches 40% of the value corresponding to their dissimilarity by two orders of magnitude. At the same time, 80% of this value is achieved at a twofold difference. For a particle with reduced electrical conductivity, the effect is somewhat weaker than for a particle with increased electrical conductivity, but, on the whole, the structure of the emerging flow is similar. In the entire range of the considered values of the electromagnetic action parameter, the flow is unstable and generates fluctuations. As the impact grows, the emerging toroidal vortices become more compact, clinging to the particle, but the fluctuations intensify and capture an increasing volume around the particle.