Showing papers on "Magnetic field published in 1995"
TL;DR: In this article, the authors describe the properties of the triangular flux-line lattice (FLL), which is more or less perturbed by material inhomogeneities that pin the flux lines, and also by thermal fluctuations.
Abstract: Magnetic flux can penetrate a type-II superconductor in the form of Abrikosov vortices (also called flux lines, flux tubes, or fluxons) each carrying a quantum of magnetic flux phi 0=h/2e. These tiny vortices of supercurrent tend to arrange themselves in a triangular flux-line lattice (FLL), which is more or less perturbed by material inhomogeneities that pin the flux lines, and in high-Tc superconductors (HTSCs) also by thermal fluctuations. Many properties of the FLL are well described by the phenomenological Ginzburg-Landau theory or by the electromagnetic London theory, which treats the vortex core as a singularity. In Nb alloys and HTSCs the FLL is very soft mainly because of the large magnetic penetration depth lambda . The shear modulus of the FLL is c66~1/ lambda 2, and the tilt modulus c44(k)~(1+k2 lambda 2)-1 is dispersive and becomes very small for short distortion wavelengths 2 pi /k<< lambda . This softness is enhanced further by the pronounced anisotropy and layered structure of HTSCs, which strongly increases the penetration depth for currents along the c axis of these (nearly uniaxial) crystals and may even cause a decoupling of two-dimensional vortex lattices in the Cu-O layers. Thermal fluctuations and softening may `melt` the FLL and cause thermally activated depinning of the flux lines or ofthe two-dimensional `pancake vortices` in the layers. Various phase transitions are predicted for the FLL in layered HTSCs. Although large pinning forces and high critical currents have been achieved, the small depinning energy so far prevents the application of HTSCs as conductors at high temperatures except in cases when the applied current and the surrounding magnetic field are small.
866 citations
TL;DR: In this article, a three-dimensional, self-consistent numerical model of the geodynamo is described, which maintains a magnetic field for over 40,000 years, including a successful reversal of the dipole moment.
Abstract: A three-dimensional, self-consistent numerical model of the geodynamo is described, that maintains a magnetic field for over 40,000 years. The model, which incorporates a finitely conducting inner core, undergoes several polarity excursions and then, near the end of the simulation, a successful reversal of the dipole moment. This simulated magnetic field reversal shares some features with real reversals of the geomagnetic field, and may provide insight into the geomagnetic reversal mechanism.
779 citations
TL;DR: In this article, an electronic phase transition of the first order, which can be caused by an external magnetic field, was discovered in Nd 1/2 Sr 1 /2 MnO 3, where the hysteretic field region was observed to depend critically on temperature and to drastically expand with a decrease of temperature.
Abstract: An electronic (metal-to-insulator) phase transition of the first order, which can be caused by an external magnetic field, was discovered in Nd 1/2 Sr 1/2 MnO 3 . A clear hysteresis was observed during the increase and decrease of an external magnetic field at a fixed temperature. The hysteretic field region was observed to depend critically on temperature and to drastically expand with a decrease of temperature, perhaps as a result of suppression of the effect of thermal fluctuations on the first-order phase transition. Although it has seldom been observed, this is thought to be a generic feature of the first-order phase transition at low temperatures near 0 kelvin.
725 citations
TL;DR: In this article, the authors presented the first 3D, time-dependent, self-consistent numerical solution of the magneto- hydrodynamic (MHD) equations that describe thermal convection and magnetic field generation in a rapidly rotating spherical fluid shell with a solid conducting inner core.
583 citations
TL;DR: In this paper, the suppression of turbulence by the E×B flow shear and parallel Flow Shear in an arbitrary shape finite aspect ratio tokamak plasma using the two point nonlinear analysis was investigated.
Abstract: The suppression of turbulence by the E×B flow shear and parallel flow shear is studied in an arbitrary shape finite aspect ratio tokamak plasma using the two point nonlinear analysis previously utilized in a high aspect ratio tokamak plasma [Phys. Plasmas 1, 2940 (1994)]. The result shows that only the E×B flow shear is responsible for the suppression of flute‐like fluctuations. This suppression occurs regardless of the plasma rotation direction and is, therefore, relevant for the very high (VH) mode plasma core as well as for the high (H) mode plasma edge. Experimentally observed in–out asymmetry of fluctuation reduction behavior can be addressed in the context of flux expansion and magnetic field pitch variation on a given flux surface. The adverse effect of neutral particles on confinement improvement is also discussed in the context of the charge exchange induced parallel momentum damping.
552 citations
TL;DR: In this paper, a brief review of the present understanding of the transitions between integer quantized plateaus of the Hall conductivity in two-dimensional disordered systems in a strong magnetic field is given.
Abstract: A brief review is given of the present understanding of the transitions between integer quantized plateaus of the Hall conductivity in two-dimensional disordered systems in a strong magnetic field. The similarity to continuous thermodynamic phase transitions is emphasized. Results of numerical simulations for non-interacting electrons are presented and compared to experiment. The role of the Coulomb interactions at the integer quantum Hall transitions is studied.
550 citations
TL;DR: In this article, it was shown that the local spin moments and the charge carriers can in turn be coupled strongly to changes in the structure of perovskites, and that the crystal structure of the compound can be switched by application of an external magnetic field.
Abstract: A VAST number of compounds are known that exhibit structure transformations in response to changes in temperature, pressure and/or composition. One such example is the family of perovskites, La1-xSrxMnO33 for a limited range of compositions (x), they undergo a structural phase transition from an orthorhombic to a rhombohedral form with increasing temperature1, 2. These compounds are also ferromagnetic, a property that arises from coupling between the charge carriers and localized spin moments of the manganese ions3–7. Here we show that, through careful tuning of the composition, the local spin moments and the charge carriers can in turn be coupled strongly to changes in the structure. For x = 0.170, the crystal structure of the compound can be switched—reversibly or irreversibly, depending on the temperature—by application of an external magnetic field.
518 citations
TL;DR: In this article, an investigation into the electron temperature perturbations associated with tearing modes in tokamak plasmas was made, and it was found that there is a critical magnetic island width below which the conventional picture where the temperature is flattened inside the separatrix is invalid.
Abstract: An investigation is made into the electron temperature perturbations associated with tearing modes in tokamak plasmas. It is found that there is a critical magnetic island width below which the conventional picture where the temperature is flattened inside the separatrix is invalid. This effect comes about because of the stagnation of magnetic field lines in the vicinity of the rational surface and the finite parallel thermal conductivity of the plasma. Islands whose widths lie below the critical value are not destabilized by the perturbed bootstrap current, unlike conventional magnetic islands. This effect may provide an explanation for some puzzling experimental results regarding error field‐induced magnetic reconnection. The critical island width is found to be fairly substantial in conventional tokamak plasmas, provided that the long mean‐free path nature of parallel heat transport and the anomalous nature of perpendicular heat transport are taken into account in the calculation.
512 citations
TL;DR: In this paper, the authors show that magnetic reconnection may also occur in three dimensions in the absence of neutral points at so-called quasi-separatrix layers, where there is a steep gradient in field line linkage.
Abstract: In two or three dimensions, magnetic reconnection may occur at neutral points and is accompanied by the transport of magnetic field lines across separatrices, the field lines (or flux surfaces in three dimensions) at which the mapping of field lines is discontinuous. Here we show that reconnection may also occur in three dimensions in the absence of neutral points at so-called “quasi-separatrix layers,” where there is a steep gradient in field line linkage. Reconnection is a global property, and so, in order to determine where it can occur, the first step is to enclose the volume being considered by a boundary (such as a spherical surface). Then the mapping of field lines from one part of the boundary to another is determined, and quasi-separatrix layers may be identified as regions where the gradient of the mapping or its inverse is very much larger than normal. The most effective measure of the presence of such layers is the norm of the displacement gradient tensor; their qualitative location is robust and insensitive to the particular surface that is chosen. Reconnection itself occurs when there is a breakdown of ideal MHD and a change of connectivity of plasma elements, where the field line velocity becomes larger than the plasma velocity, so that the field lines slip through the plasma. This breakdown can occur in the quasi-separatrix layers with an electric field component parallel to the magnetic field. In three dimensions the electric field E (and therefore the field line velocity v⊥) depends partly on the imposed values of E (or v⊥) at the boundary and partly on the gradients of the inverse mapping function. We show that the inverse mapping determines the location of the narrow layers where the breakdown of ideal MHD can occur, while the imposed boundary values of v⊥ determine mainly the detailed flow pattern inside the layers. Thus, in general, E (and therefore v⊥) becomes much larger than its boundary values at locations where the gradients of the inverse mapping function are large. An example is given of a sheared X field, where a slow smooth continuous shear flow imposed on the boundary across one quasi-separatrix produces a flipping of magnetic field lines as they slip rapidly through the plasma in the other quasi-separatrix layer. It results in a strong plasma jetting localized in, and parallel to, the separatrix layers.
481 citations
TL;DR: In this article, the present status of magnetic resonance force microscopy (MRFM) technology, with particular attention to the feasibility of detecting single-electron magnetic moments, and the possible applications of MRFM in biological imaging.
Abstract: Recent initial experiments in magnetic resonance force microscopy (MRFM) have detected the magnetic force exerted by electrons and nuclei in microscopic samples. The experiments generate a force signal by modulating the sample magnetization with standard magnetic resonance techniques. Sample sizes of a few nanograms generate readily detected force signals of order ${10}^{\ensuremath{-}14}$ to ${10}^{\ensuremath{-}16}$ Newtons. This article describes the present status of MRFM technology, with particular attention to the feasibility of detecting single-electron magnetic moments, and the possible applications of MRFM in biological imaging.
390 citations
TL;DR: A new magnetic field sensor is presented, based on perpendicular hot electron transport in a giant magnetoresistance (Co/Cu)4 multilayer, which serves as a base region of an n-silicon metal-base transistor structure, which allows the investigation of energy resolved perpendicular transport properties, and in particular spin-dependent scattering of hot electrons in transition-metal as well as rare-earth-based multilayers.
Abstract: A new magnetic field sensor is presented, based on perpendicular hot electron transport in a giant magnetoresistance (Co/Cu)4 multilayer, which serves as a base region of an n-silicon metal-base transistor structure. A 215% change in collector current is found in 500 Oe (77 K), with typical characteristics of the spin-valve effect. The in-plane magnetoresistance was only 3%. The transistor structure allows the investigation of energy resolved perpendicular transport properties, and in particular spin-dependent scattering of hot electrons in transition-metal as well as rare-earth-based multilayers.
TL;DR: In this article, the authors evaluated the properties of magnetometers with the framework of the Landau theory for the second order phase transition or the thermodynamics in magnetic fields, and compared the results with direct experimental results as well as those obtained using the molecular field model.
Abstract: Magnetic refrigeration, an emerging new technology for cooling and gas liquefaction, needs magnetic materials with specific thermomagnetic behavior. Depending on the thermodynamic cycle selected, the isothermal magnetic entropy change or the adiabatic temperature change upon field application needs to be a preselected function of temperature. To obtain these properties, most designers rely on calorimetry, an expensive and time consuming technique. The present article describes that, classical magnetic measurements, when evaluated within the framework of the Landau theory for the second order phase transition or the thermodynamics in magnetic fields, are able to provide the preliminary information needed for the design of magnetic refrigerators. After reviewing the theory, experimental results on ferromagnetic gadolinium (Gd) and helimagnetic dysprosium (Dy) are analyzed and compared to direct experimental results as well as to those obtained using the molecular field model. The results demonstrate the reproducibility of entropy calculations and the good agreement between the experimental and the calculated specific heat anomalies. While the molecular field theory which assumes simple ferromagnetic order clearly fails for helimagnetic dysprosium, an analysis of the experimental data based on the Landau theory gives reliable results. Besides, the field and temperature dependencies of the isothermal magnetic entropy change allows one to characterize the magnetic structure (nature of the magnetic order) of the sample. Furthermore, magnetic measurements define the useful field range and provide information on transitions that influence the thermal behavior and magnetic losses.
TL;DR: A detailed comparison is made between the tearing-type modes observed in TFTR supershot plasmas and the nonlinear, neoclassical pressure-gradient--driven tearing mode theory, finding good agreement on the non linear evolution of single helicity magnetic islands.
Abstract: A detailed comparison is made between the tearing-type modes observed in TFTR supershot plasmas and the nonlinear, neoclassical pressure-gradient--driven tearing mode theory. Good agreement is found on the nonlinear evolution of single helicity magnetic islands $(m/n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3/2$, $4/3$, or $5/4$, where $m$ and $n$ are the poloidal and toroidal mode numbers, respectively). The saturation of these neoclassical tearing-type modes requires ${\ensuremath{\Delta}}^{\ensuremath{'}}l0$ (where ${\ensuremath{\Delta}}^{\ensuremath{'}}$ is the well-known parameter for classical current-driven tearing instability), which is also consistent with the numerical calculation using the experimental data.
TL;DR: The viscosity of quantum fluids with an energy gap at zero temperature is non-dissipative and is related to the adiabatic curvature on the space of flat background metrics (which plays the role of the parameter space).
Abstract: The viscosity of quantum fluids with an energy gap at zero temperature is related to the adiabatic curvature on the space parametrizing flat background metrics. For quantum Hall fluids on two-dimensional tori, the quantum viscosity is computed. It turns out to be isotropic, constant, and proportional to the magnetic field strength.
TL;DR: In this article, a mini-magnet fabricated from four melt-textured YBa2Cu3O7 - delta (MT-YBCO) discs activated at 49 K using an applied field of 14 T was observed to crack.
Abstract: Quasi-permanent magnets made of melt-textured YBa2Cu3O7 - delta (MT-YBCO) superconductor can now trap multi-tesla fields, B sub t. The interaction of the trapped field and the critical current causes an outward pressure, proportional to B sub t (2), which can crack the magnet. The authors have done an experiment to observe such cracking in a mini-magnet fabricated from four MT-YBCO discs activated at 49 K using an applied field of 14 T. They have compared the results to existing theories which describe magnetic pressure in a trapped-field magnet (TFM) previously activated. They find that a modification is needed to describe magnetic pressure during the process of activation. They present the experimental results and the expanded theory, based on the simple Bean model. Theory and experiment show good agreement. The authors find that cracking is more likely during activation, and conclude that 10 T is achievable in TFM`s composed of present materials. Cracking is most probable at the center of a TFM, with the cracks running radially outward.
TL;DR: The authors have reformulated outer sphere relaxation theory to incorporate progressive magnetic saturation of solute nanoparticles and indicate how to use empirical magnetization data for realistic particles when their magnetic properties are not ideal.
Abstract: Organically coated iron oxide crystallites with diameters of 5-50 nm ("nanoparticles") are potential magnetic resonance imaging contrast agents. 1/T1 and 1/T2 of solvent water protons are increased dramatically by magnetic interactions in the "outer sphere" environment of the nanoparticles; subsequent diffusive mixing distributes this relaxation throughout the solvent. Published theory, valid for the solute magnetic energy small compared with thermal energy, is applicable to small magnetic solutes (e.g., gadolinium and manganese diethylenetriaminopentaacetic acid, and nitroxide free radicals) at generally accessible fields (< or = 50 T). It fails for nanoparticles at fields above approximately 0.05 T, i.e., at most imaging fields. The authors have reformulated outer sphere relaxation theory to incorporate progressive magnetic saturation of solute nanoparticles and, in addition, indicate how to use empirical magnetization data for realistic particles when their magnetic properties are not ideal. It is important to handle the effects of rapid thermally induced reorientation of the magnetization of the nanoparticles (their "superparamagnetism") effectively, including their sensitivity to particle size. The theoretical results are presented as the magnetic field dependence (NMRD profiles) of 1/T1 and 1/T2, normalized to Fe content, for three sizes of particles, and then compared with the limited data extant for well-characterized material.
TL;DR: In this paper, an analysis of magnetic braking of a rotating star by the disk due to field-line twisting is presented, where it is shown that magnetic braking can give spin-up or spin-down (or no spin change) of the star depending mainly on the star's magnetic moment and the mass accretion rate.
Abstract: An investigation is made of disk accretion of matter onto a rotating star with an aligned dipole magnetic field. A new aspect of this work is that when the angular velocity of the star and disk differ substantially we argue that the $\bf B$ field linking the star and disk rapidly inflates to give regions of open field lines extending from the polar caps of the star and from the disk. The open field line region of the disk leads to the possibility of magnetically driven outflows. An analysis is made of the outflows and their back affect on the disk structure assuming an ``$\ap$" turbulent viscosity model for the disk and a magnetic diffusivity comparable to this viscosity. The outflows are found to extend over a range of radial distances inward to a distance close to $r_{to}$, which is the distance of the maximum of the angular rotation rate of the disk. We find that $r_{to}$ depends on the star's magnetic moment, the accretion rate, and the disk's magnetic diffusivity. The outflow regime is accompanied in general by a spin-up of the rotation rate of the star. When $r_{to}$ exceeds the star's corotation radius $r_{cr} = (GM/\om_*^2)^{1\ov 3}$, we argue that outflow solutions do not occur, but instead that ``magnetic braking" of the star by the disk due to field-line twisting occurs in the vicinity of $r_{cr}$. The magnetic braking solutions can give spin-up or spin-down (or no spin change) of the star depending mainly on the star's magnetic moment and the mass accretion rate. For a system with $r_{to}$ comparable to $r_{cr}$, bimodal behavior is possible where extraneous perturbations cause the system to flip between spin-up and spin-down.
TL;DR: Analysis of spectral discontinuities obtained for different isotopes and magnetic field strengths and a method of readily obtaining very broad spectra without point by point acquisition demonstrate an approach that should be very useful in constraining the chemical shifts and quadrupole parameters involved in solid-state gallium NMR spectra.
TL;DR: The deposition of ferromagnetic microstructures on top of a high-mobility two-dimensional electron gas (2DEG) allows the investigation of electron transport in a periodic magnetic field which alternates on a length scale small compared to the elastic mean free path of the electrons.
Abstract: The deposition of ferromagnetic microstructures on top of a high-mobility two-dimensional electron gas (2DEG) allows the investigation of electron transport in a periodic magnetic field which alternates on a length scale small compared to the elastic mean free path of the electrons. The longitudinal resistance of the 2DEG displays, as a function of the externally applied field, the long-predicted magnetic commensurability oscillations which result from the interplay between the two characteristic length scales of the system, the classical cyclotron radius ${R}_{c}$ of the electrons and the period $a$ of the magnetic field modulation.
TL;DR: In this paper, the microwave surface resistance (30-60 GHz) for different crystallographic orientations in the vortex state was measured and a sharp magnetoabsorption resonance was observed.
Abstract: We have measured the microwave surface resistance (30-60 GHz) for different crystallographic orientations in the vortex state of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$. A sharp magnetoabsorption resonance is observed below ${T}_{c}$ when ac electric fields and magnetic fields are applied parallel to the $c$ axis (${E}_{\mathrm{ac}}\ensuremath{\parallel}B\ensuremath{\parallel}c$). We argue that the observed resonance arises from collective Josephson plasma oscillations generated by interlayer Josephson currents. From the frequency and temperature dependence of the resonance, we discuss the interlayer phase coherence in the vortex liquid and solid states quantitatively.
TL;DR: In this paper, a comprehensive two-fluid model is developed for collective modes in a nonrelativistic electron-positron plasma, both in the presence and absence of a magnetic field.
Abstract: A comprehensive two-fluid model is developed for collective modes in a nonrelativistic electron-positron plasma. Longitudinal and transverse electrostatic and electromagnetic modes, both in the presence and absence of a magnetic field, are studied. Wave properties are discussed in terms of dispersion relations, wave normal surfaces, and cylindrical mirror analyzer clemmow-Mullaly-Allis diagrams. The results are extended to include the two-stream instability and ion acoustic solitary waves. For the two-stream instability, a similar result is found as in the electron-ion plasma. For ion acoustic solitary waves, only subsonic solutions are found to exist. Furthermore, their width is proportional to their amplitude, unlike the electron-ion plasma case, where the speed is proportional to the amplitude.
TL;DR: In experiments on resonant tunneling through a "quantum antidot" (a potential hill) in the quantum Hall (QH) regime, periodic conductance peaks were observed as a function of both magnetic field and back gate voltage, implying that charge deficiency on the antidot is quantized in units of the charge of quasi-particles of the surrounding QH condensate.
Abstract: In experiments on resonant tunneling through a "quantum antidot" (a potential hill) in the quantum Hall (QH) regime, periodic conductance peaks were observed as a function of both magnetic field and back gate voltage. A combination of the two periods constitutes a measurement of the charge of the tunneling particles and implies that charge deficiency on the antidot is quantized in units of the charge of quasi-particles of the surrounding QH condensate. The experimentally determined value of the electron charge e is 1.57 x 10–19 coulomb = (0.98 ± 0.03) e for the states v = 1 and v = 2 of the integer QH effect, and the quasi-particle charge is 5.20 x 10–20 coulomb = (0.325 ± 0.01)e for the state v = ⅓ of the fractional QH effect.
TL;DR: It is explained Barkhausen noise in magnetic systems in terms of avalanches of domains near a plain old critical point in the hysteretic zero-temperature random-field Ising model, making nontrivial predictions of the shape of the distribution up to 50{percent} above the critical point.
Abstract: We explain Barkhausen noise in magnetic systems in terms of avalanches of domains near a plain old critical point in the hysteretic zero-temperature random-field Ising model. The avalanche size distribution has a universal scaling function, making nontrivial predictions of the shape of the distribution up to 50{percent} above the critical point, where two decades of scaling are still observed. We simulate systems with up to 1000{sup 3} domains, extract critical exponents in 2, 3, 4, and 5 dimensions, compare with our 2D and 6{minus}{epsilon} predictions, and compare to a variety of experiments. {copyright} {ital 1995 The American Physical Society.}
TL;DR: Magneto-optical investigations of the flux distributions in high-Tc superconductors are reviewed in this article, where various techniques (which are all based on the Faraday effect) are compared with each other concerning resolution and working range of temperature and external magnetic field.
Abstract: Magneto-optical investigations of the flux distributions in high-Tc superconductors are reviewed. The various techniques (which are all based on the Faraday effect) are compared with each other concerning resolution and working range of temperature and external magnetic field. A short description of the historical development of the magneto-optical methods is given and the existing equipment is classified. Various aspects of flux visualization are presented acid special observations made by means of magneto-optical techniques are shown. The capability of the magneto-optical techniques to observe dynamic processes allows observation of flux motion due to thermal activation or even quantum creep, and under the influence of transport currents. It is shown that magneto-optical techniques are a unique tool to show that flux patterns are extremely sensitive to the presence of defects.
TL;DR: The elastic energy and stability of a singular loop of wedge disclination and the first-order transition of the radial hedgehog into a wide singular loop, driven by an external magnetic field are analyzed.
Abstract: A suspended particle with specific director anchoring on its surface introduces a complex distortion field in a nematic liquid crystal matrix. Topological defects---disclination loops, boojums, and hedgehogs, are needed to match the director near the particle surface with that at the far distance, which is determined by boundary conditions on the sample. This paper analyzes the elastic energy and stability of a singular loop of wedge disclination and the first-order transition of the radial hedgehog into a wide singular loop, driven by an external magnetic field. The far field of distortions, created by a ``Saturn ring'' of disclination around the spherical radial particle, allows one to calculate the potential of interaction between such particles and with the surface of the liquid crystal. Particles are repelled from each other and from the rigidly anchored surface with the potential U\ensuremath{\sim}1/${\mathit{r}}^{3}$. If the sample surface has soft anchoring, the particle is attracted to it at close distances and is repelled, if beyond the anchoring coherence length ${\ensuremath{\xi}}_{\mathit{w}}$. Several experiments to test these conclusions are suggested.
TL;DR: In this paper, the boundary layer flow due to a plate stretching with a power-law velocity distribution in the presence of a transverse magnetic field is studied, and an accurate expression for the skin friction coefficient is derived using Crocco's transformation.
TL;DR: HYDRA is an experimental hot plasma investigation for the POLAR spacecraft of the GGS program as discussed by the authors, with a suite of particle analyzers that sample the velocity space of electron and ions between 2 keV/q and 35 keV /q in three dimensions, with a routine time resolution of 05 s.
Abstract: HYDRA is an experimental hot plasma investigation for the POLAR spacecraft of the GGS program A consortium of institutions has designed a suite of particle analyzers that sample the velocity space of electron and ions between ≃2 keV/q – 35 keV/q in three dimensions, with a routine time resolution of 05 s Routine coverage of velocity space will be accomplished with an angular homogeneity assumption of ≃16°, appropriate for subsonic plasmas, but with special ≃15° resolution for electrons with energies between 100 eV and 10 keV along and opposed to the local magnetic field This instrument produces 49 kilobits s−1 to the telemetry, consumes on average 14 W and requires 187 kg for deployment including its internal shielding The scientific objectives for the polar magnetosphere fall into four broad categories: (1) those to define the ambient kinetic regimes of ions and electrons; (2) those to elucidate the magnetohydrodynamic responses in these regimes; (3) those to assess the particle populations with high time resolution; and (4) those to determine the global topology of the magnetic field In thefirst group are issues of identifying the origins of particles at high magnetic latitudes, their energization, the altitude dependence of the forces, including parallel electric fields they have traversed In thesecond group are the physics of the fluid flows, regimes of current, and plasma depletion zones during quiescent and disturbed magnetic conditions In thethird group is the exploration of the processes that accompany the rapid time variations known to occur in the auroral zone, cusp and entry layers as they affect the flow of mass, momentum and energy in the auroral region In thefourth class of objectives are studies in conjunction with the SWE measurements of the Strahl in the solar wind that exploit the small gyroradius of thermal electrons to detect those magnetic field lines that penetrate the auroral region that are directly ‘open’ to interplanetary space where, for example, the Polar Rain is observed
TL;DR: In this article, the authors present two-dimensional hydrodynamical simulations of corotating stream structure in the wind from a rotating O star, together with resulting synthetic line profiles showing discrete absorption components.
Abstract: We present two-dimensional hydrodynamical simulations of corotating stream structure in the wind from a rotating O star, together with resulting synthetic line profiles showing discrete absorption components (DACs). An azimuthal variation is induced by a local increase or decrease in the radiative driving force, as would arise from a bright or dark ``star spot'' in the equatorial plane. Since much of the emergent wind structure seems independent of the exact method of perturbation, we expect similar morphology in winds perturbed by localized magnetic fields or nonradial pulsations, as well as by either rotationally-modulated structure or transient mass ejections. We find that bright spots with enhanced driving generate high-density, low-speed streams, while dark spots generate low-density, high-speed streams. Corotating interaction regions (CIRs) form where fast material collides with slow material -- e.g. at the leading (trailing) edge of a stream from a dark (bright) spot, often steepening into shocks. The unperturbed supersonic wind obliquely impacts the high-density CIR and sends back a nonlinear signal which takes the form of a sharp propagating discontinuity (``kink'' or ``plateau'') in the radial velocity gradient. These features travel inward in the co-moving frame at the radiative-acoustic characteristic speed, and thus slowly outward in the star's frame. We find that these slow kinks, rather than the CIRs themselves, are more likely to result in high-opacity DACs in the absorption troughs of unsaturated P Cygni line profiles.