Flux Injection Research Articles

Tropospheric forcing of the stratosphere: A comparative study of the two different major stratospheric warmings in 2009 and 2010

In January 2009 and 2010, two major stratospheric warmings (MSWs) took place in the boreal polar stratosphere. Both MSWs were preceded by nearly the strongest injection of tropospheric wave activity on record since 1958 and their central date was almost coincident. However, the typical external factors that influence the occurrence of MSWs (the Quasi-Biennial Oscillation, sunspot cycle, or El Nio) were dissimilar in the two midwinters: favorable in 2010 but unfavorable in 2009. In this study, the driving mechanisms of these two different MSWs were investigated focusing on the amplification of upward wave activity injection into the stratosphere before the MSW onset. By decomposing the total wave flux injection into contributions from the climatological planetary waves and from deviations from the latter we found clear differences in this amplification between both MSWs. The pre-MSW period in 2009 was characterized by a peak in the 100 hPa eddy heat flux with a predominance of wave number 2 activity. This was due to strong anomalies associated with Rossby wave packets originating from a deep ridge over the eastern Pacific. In contrast, the amplification of the upward wave propagation prior to the 2010 MSW was equally due to Rossby wave packets and to the interaction between the latter and the climatological waves. This amplification enhanced wave number 1 stationary waves in January 2010, which seemed at least partially due to the 2009/2010 El Nio event. Our results show the relevance of the internal tropospheric variability in generating MSWs, particularly when the external factors do not play any role. © 2011 by the American Geophysical Union.

Zero-β modeling of coaxial helicity injection in the HIT-II spherical torus

Coaxial helicity injection in the HIT-II [A. J. Redd et al., Phys. Plasmas 9, 2006 (2002)] spherical torus is modeled with time-dependent resistive magnetohydrodynamics computations run to steady state for conditions without strong relaxation. Laboratory and computed results on injector current and plasma current agree reasonably well as toroidal magnetic field and injector flux are scaled. The scalings are consistent with a dimensional estimate from the Grad-Shafranov equation that provides a new perspective on a previously published model based on a current-sheet equilibrium and the magnetic pressure required for the “bubble-burst” criterion. Numerical solutions of the Grad-Shafranov equation with an assumed current profile also indicate large qualitative changes as the predicted criterion is crossed.

ACCELERATION OF CORONAL MASS EJECTIONS FROM THREE-DIMENSIONAL RECONSTRUCTION OFSTEREOIMAGES

We employ a three-dimensional (3D) reconstruction technique, for the first time to study the kinematics of six coronal mass ejections (CMEs), using images obtained from the COR1 and COR2 coronagraphs on board the twin STEREO spacecraft, as also the eruptive prominences (EPs) associated with three of them using images from the Extreme UltraViolet Imager (EUVI). A feature in the EPs and leading edges (LEs) of all the CMEs was identified and tracked in images from the two spacecraft, and a stereoscopic reconstruction technique was used to determine the 3D coordinates of these features. True velocity and acceleration were determined from the temporal evolution of the true height of the CME features. Our study of kinematics of the CMEs in 3D reveals that the CME leading edge undergoes maximum acceleration typically below 2R$_\{odot}$. The acceleration profiles of CMEs associated with flares and prominences exhibit different behaviour. While the CMEs not associated with prominences show a bimodal acceleration profile, those associated with prominences do not. Two of the three associated prominences in the study show a high and rising value of acceleration up to a distance of almost 4R$_\{odot}$ but acceleration of the corresponding CME LE does not show the same behaviour, suggesting that the two may not be always driven by the same mechanism. One of the CMEs, although associated with a C-class flare showed unusually high acceleration of over 1500 m s$^{-2}$. Our results therefore suggest that only the flare-associated CMEs undergo residual acceleration, which indicates that the flux injection theoretical model holds good for the flare-associated CMEs, but a different mechanism should be considered for EP-associated CMEs.

Coupled Thermal-Magnetic Analysis on Thermally Actuated Superconducting Flux Pump

This paper presents numerical analysis of the thermally actuated superconducting flux pump. Visualization of the behavior of the magnetic flux helps our understanding of flux injection mechanism. In addition, in order to confirm validity of the result, we conducted a preliminary flux pump experiment. This result qualitatively agrees well with the experimental one. The flux pump system utilizes a particular behavior that permeability of some materials such as Gadolinium is sensitive to the temperature. In this paper a simple heater is used to control the flux pump system.

Helicity Injection Fluxes of Twist and Writhe

We consider helicity flux equations proposed by previous authors and offer interpretations of these helicity injection equations with twist and writhe. At first, comparing Pariat’s helicity flux equation (2005, A&A, 439, 1191) with Longcope’s (2007, ApJ, 668, 571), we find that the Pariat’s helicity injection equation shows helicity evolution of continuous magnetic field lines, which is an extreme case of the Longcope’s multiple flux tube model. Next, we investigated Berger’s helicity flux density (1984, J. Fluid Mech., 147, 133) and Pariat’s on the positive and negative polarities, and confirmed that these equations produce different helicity fluxes on the positive and negative polarities. Under the idea of the multiple flux tube model, we propose two interpretations of helicity injection fluxes of twist and writhe; the single flux tube model and the continuous field line model. Recent results of helicity flux injections need to be reanalyzed.

Solar activity due to magnetic complexity of active regions

AbstractActive regions (ARs), involved in the Halloween events during October-November 2003, were the source of unusual activity during the following solar rotation. The flares on 18-20 November 2003 that occur in the AR NOAA10501 were accompanied by coronal mass ejections associated to some particularly geoeffective magnetic clouds.Our analysis of the magnetic flux and helicity injection revealed that a new emerging bipole and consequent shearing motions continuously energized the region during its disk passage. The stored energy was eventually released through the interaction of the various systems of magnetic loops by several magnetic reconnection events. Active events on November 18 (filament eruptions and CMEs) were originated by shearing motions along a section of the filament channel that injected magnetic helicity with sign opposite to that of the AR. Two homologous flares, that occurred on November 20, were apparently triggered by different mechanisms as inferred from the flare ribbons evolution (filament eruption and CMEs). We studied in detail the behaviour of two North-South oriented filaments on November 20 2003. They merged and split following a process suggestive of ‘sling-shot’ reconnection between two coronal flux ropes. We successfully tested this scenario in a 3D MHD simulation that is presented in this paper.

TEMPORAL AND PHYSICAL CONNECTION BETWEEN CORONAL MASS EJECTIONS AND FLARES

The physical connection between the eruption of coronal mass ejections (CMEs) and associated flare energy release is examined. The trajectories of five CMEs are determined using LASCO/SOHO or SECCHI/STEREO data, and the associated soft X-ray (SXR) light curves are obtained from GOES 1-8 A data. As the theoretical description of CME physics, the existing erupting flux-rope model is used in which an initial flux rope is driven out of equilibrium by the increasing poloidal magnetic flux {Phi}{sub p}(t) (poloidal 'flux injection'). Mathematically, this is represented by d{Phi}{sub p}(t)/dt. For each CME, this function is adjusted to obtain the solution that best fits the observed height-time data. The resulting d{Phi}{sub p}(t)/dt is shown to be strongly constrained by the CME height data. This function and the attendant electromotive force (EMF) given by E(t){identical_to}-(1/c)d{Phi}{sub p}(t)/dt constitute predictions of the theory for each CME trajectory. It is shown that the best-fit solutions fit the CME trajectories within 1%-2% of the CME height data and that the temporal profile of the predicted d{Phi} {sub p}(t)/dt is correlated with that of the associated X-ray light curve regardless of the flare duration. Specifically, we find that the observed duration of SXR emission {Delta}T{sub SXR} is comparablemore » to and scales with the predicted duration {Delta}T{sub p} of poloidal flux injection, i.e., {Delta}T{sub SXR} {approx_equal} {Delta}T{sub p} . Neither the predicted d{Phi} {sub p}(t)/dt nor the input CME height data contain any information on X-ray data. Thus, the correlation is nontrivial, constituting evidence that poloidal flux injection is physically connected to flare energy release. It is suggested that this connection is provided by the EMF that produces electric fields to accelerate particles.« less

Effects of dilute columnar defects on the vortex matter in Bi 2Sr 2CaCu 2O 8+δ near the disorder-driven phase transition

Magneto-optical measurements are employed to characterize the disorder-driven vortex phase transition and the metastable disordered vortex state in heavy-ion irradiated and pristine regions of the same Bi 2Sr 2CaCu 2O 8+δ crystal. We find that dilute columnar defects, while hardly affect the disorder-driven phase transition line, significantly increase the lifetime of the metastable state created in the vicinity of this line. Study of flux injection from the pristine region into the irradiated region suggests that in presence of columnar defects a metastable disordered state may be created in the bulk, in addition to being injected from the edges.

THE PHOTOSPHERIC ENERGY AND HELICITY BUDGETS OF THE FLUX-INJECTION HYPOTHESIS

The flux-injection hypothesis for driving coronal mass ejections (CMEs) requires the transport of substantial magnetic energy and helicity flux through the photosphere concomitant with the eruption. Under the magnetohydrodynamics approximation, these fluxes are produced by twisting magnetic field and/or flux emergence in the photosphere. A CME trajectory, observed 2000 September 12 and fitted with a flux-rope model constrains energy and helicity budgets for testing the flux-injection hypothesis. Optimal velocity profiles for several driving scenarios are estimated by minimizing the photospheric plasma velocities for a cylindrically symmetric flux-rope magnetic field subject to the flux budgets required by the flux-rope model. Ideal flux injection, involving only flux emergence, requires hypersonic upflows in excess of the solar escape velocity 617 km/s over an area of 6x10^8 km^2 to satisfy the energy and helicity budgets of the flux-rope model. These estimates are compared with magnetic field and Doppler measurements from Solar Heliospheric Observatory/Michelson Doppler Imager on 2000 September 12 at the footpoints of the CME. The observed Doppler signatures are insufficient to account for the required energy and helicity budgets of the flux-injection hypothesis.

SMALL MAGNETIC LOOPS CONNECTING THE QUIET SURFACE AND THE HOT OUTER ATMOSPHERE OF THE SUN

Sunspots are the most spectacular manifestation of solar magnetism, yet 99% of the solar surface remains "quiet" at any time of the solar cycle. The quiet sun is not void of magnetic fields, though; they are organized at smaller spatial scales and evolve relatively fast, which makes them difficult to detect. Thus, although extensive quiet Sun magnetism would be a natural driver to a uniform, steady heating of the outer solar atmosphere, it is not clear what the physical processes involved would be, due to lack of observational evidence. We report on the topology and dynamics of the magnetic field in very quiet regions of the Sun from spectropolarimetric observations of the Hinode satellite, showing a continuous injection of magnetic flux with a well-organized topology of Ω-loop from below the solar surface into the upper layers. At first stages, when the loop travels across the photosphere, it has a flattened (staple-like) geometry and a mean velocity ascent of ∼3 km s−1. When the loop crosses the minimum temperature region, the magnetic fields at the footpoints become almost vertical and the loop topology resembles a potential field. The mean ascent velocity at chromospheric height is ∼12 km s−1. The energy input rate of these small-scale loops in the lower boundary of the chromosphere is (at least) of 1.4 × 106–2.2 × 107 erg cm−2 s−1. Our findings provide empirical evidence for solar magnetism as a multi-scale system, in which small-scale low-flux magnetism plays a crucial role, at least as important as active regions, coupling different layers of the solar atmosphere and being an important ingredient for chromospheric and coronal heating models.

Demonstration of Tokamak Ohmic Flux Saving by Transient Coaxial Helicity Injection in the National Spherical Torus Experiment

Transient coaxial helicity injection (CHI) started discharges in the National Spherical Torus Experiment (NSTX) have attained peak currents up to 300 kA and when coupled to induction, it has produced up to 200 kA additional current over inductive-only operation. CHI in NSTX has shown to be energetically quite efficient, producing a plasma current of about 10 A/J of capacitor bank energy. In addition, for the first time, the CHI-produced toroidal current that couples to induction continues to increase with the energy supplied by the CHI power supply at otherwise similar values of the injector flux, indicating the potential for substantial current generation capability by CHI in NSTX and in future toroidal devices.

Validation of a code for modeling cavitation phenomena in Diesel injector nozzles

In this paper, the validity of a code implemented for OpenFOAM ® for modeling cavitation phenomena has been checked by comparing data acquired by numerical simulations against data obtained for a simple contraction nozzle and for a real diesel injector nozzle. The comparison of numerical and experimental data has been performed, for the simple nozzle, in terms of mass flow rate, velocity at the exit and pressure and cavitation distributions. The numerical results for the real diesel nozzle geometry have been validated with experimental measurements of mass flow rate, momentum flux and effective injection velocity. The results obtained in both cases and their comparison with available experimental data showed that the model is able to predict with a high level of confidence the behavior of the fluid in such conditions.

CT Angiography: Injection and Acquisition Technique

CT scanner technology is continuously evolving, with scan times becoming shorter with each scanner generation. Achieving adequate arterial opacification synchronized with CT data acquisition is becoming increasingly difficult. A fundamental understanding of early arterial contrast medium dynamics is thus of utmost importance for the design of CT scanning and injection protocols for current and future cardiovascular CT applications. Arterial enhancement is primarily controlled by the iodine flux (injection flow rate) and the injection duration versus a patient's cardiac output and local downstream physiology. The technical capabilities of modern CT equipment require precise scan timing. Together with automated tube current modulation and weight-based injection protocols, both radiation exposure and contrast medium enhancement can be individualized.

Significance of injection modes and heterogeneity on spatial and temporal dispersion of advecting particles in two-dimensional discrete fracture networks

We investigate the impact of injection mode (flux and resident injection) and heterogeneity in hydraulic properties on dispersion of advecting particles in two-dimensional discrete fracture network models, using a Monte Carlo method. We find that the injection mode has a significant effect on dispersion: The resident injection mode exhibits anomalous features of transport whereas the flux injection mode tends to Gaussian transport; this observation is easily understood by considering phase diagrams where a limited number of particles entering low velocity fractures greatly increase macrodispersion. In spite of a sizeable portion of negative longitudinal velocities, it is shown that multiple crossings are negligible when quantifying longitudinal macrodispersion. A simple probabilistic expression of particle mass balance is shown to predict well the spatial distribution of advecting particles.

Solar Magnetic Tracking. II. The Apparent Unipolar Origin of Quiet‐Sun Flux

We investigate the origin of small-scale flux concentrations in the quiet Sun. In apparent violation of the physical requirement for flux balance, 94% of the features containing newly detected flux are unipolar at a resolution of 1.2''. We analyze 2619 of these apparent unipolar emergences in an image sequence from the SOHO MDI magnetograph and compare the ensemble average to a model of asymmetric bipolar emergence that could in principle hide opposing flux under the noise floor of MDI. We examine the statistical consequences of this mechanism and find that it cannot be responsible for more than a small fraction of the unipolar emergences. We conclude that the majority of the newly detected flux in the quiet Sun is instead due to the coalescence of previously existing but unresolved flux into concentrations that are large and strong enough to be detected. We estimate the rate of coalescence into arcsecond-scale magnetic features averaged over the solar surface to be 7 × 1021 Mx hr−1, comparable to the reported flux injection rate due to ephemeral regions. This implies that most flux in the solar network has been processed by very small scale shredding, emergence, cancellation, and/or coalescence that is not resolved at 1.2'', and it suggests that currently unresolved emergences may be at least as important as ephemeral region emergences to the overall flux budget.

On the Origin of Magnetic Helicity in the Solar Corona

Twenty-three active regions associated with pronounced sigmoidal structure in Yohkoh soft X-ray observations are selected to investigate the origin of magnetic helicity in the solar corona. We calculate the radial magnetic flux of each polarity, the rate of magnetic helicity injection, and total flux of the helicity injection ( -->? HLCT) over 4-5 days using MDI 96 minute line-of-sight magnetograms and a local correlation tracking technique. We also estimate the contribution from differential rotation to the overall helicity budget ( -->? Hrot). It is found that of the seven active regions for which the flux emergence exceeds -->1.0 ? 1022 Mx, six exhibited a helicity flux injection exceeding -->1.0 ? 1043 Mx2 (i.e., -->? H = ? HLCT ? ? Hrot). Moreover, the rate of helicity injection and the total helicity flux are larger (smaller) during periods of more (less) increase of magnetic flux. Of the remaining 16 active regions, with flux emergence less than 1022 Mx, only 4 had significant injection of helicity, exceeding 1043 Mx2. Typical contributions from differential rotation over the same period were 2-3 times smaller than that of the strong magnetic field emergence. These statistical results signify that the strong emergence of magnetic field is the most important origin of the coronal helicity, while horizontal motions and differential rotation are insufficient to explain the measured helicity injection flux. Furthermore, the study of the helicity injection in nineteen newly emerging active regions confirms the result on the important role played by strong magnetic flux emergence in controlling the injection of magnetic helicity into the solar corona.

Desulfurization Technology in the Blast Furnace Raceway by MgO–SiO2 Flux Injection

This paper presents a study on desulfurization technology in the steel industry, with attention focused on the removal of sulfur that forms acid rain, which has been creating various global problems. The study was confined to the technology that injects a mixture of serpentine and pulverized coals. Thermodynamically, a magnesium gas producing reaction occurs when magnesium oxide is turned into a hot strongly reducing atmosphere and the resulting magnesium gas forms magnesium sulfide by reaction with the sulfur in the molten iron. By dividing this desulfurization process into a magnesium gas producing reaction and a desulfurization reaction by the magnesium gas, the desulfurization effect of the magnesium oxide flux was confirmed through laboratory experiment. A thermodynamic study on the desulfurization reaction in which SiO gas resulting from the reduction of SiO2 produces a silicon sulfide gas by reaction with the sulfur in the molten iron revealed that the possibility of desulfurization of the molten iron by the silicon sulfide gas is not negligible.

Coaxial helicity injection in open-flux low-aspect-ratio toroidal discharges

Open-flux low-aspect-ratio toroidal discharges generated and sustained by coaxial helicity injection (CHI) in the Helicity Injected Torus device (HIT-II) are described. The discharges in this study are flux tubes directly connected to the CHI electrodes, with poloidal flux less than or equal to the CHI injector flux, and no possibility of a significant closed-flux plasma core. Theoretically derived scalings for the dependence of CHI injector current on the toroidal field current and magnitude of the injector flux are experimentally confirmed, and empirical models are developed for the poloidal magnetic field and toroidal plasma current in open-flux discharges. In particular, the toroidal plasma current is independent of the toroidal magnetic field, both theoretically and empirically. Variations in injector flux geometry demonstrate that the CHI injector current leaves the electrode surfaces at the flux strike points, and that the relative width of the CHI injector determines whether the dominant observed relaxation mechanism is a harmonic mode at the plasma edge or reconnection near the CHI electrodes. In the case of an effective interelectrode distance approximately equal to the device minor radius, the ratio of toroidal plasma current to CHI injector current is maximized. Global magnetic equilibrium quantities and local magnetic measurements are consistent with modelling these open-flux discharges as thin current sheets connected to the CHI electrodes.

Sustainment of FRC-equilibrium by use of a centre solenoid in TS-4

This paper addresses a basic equilibrium/confinement question whether a field reversed configuration (FRC) with a balanced amount of magnetic and thermal energies is sustained solely by inductive magnetic flux (magnetic energy) injection of a centre solenoid coil. A new finding is that preferential injection of magnetic energy causes a significant increase in thermal energy of the FRC to maintain high-beta equilibrium. The FRC plasma is concluded to have the robustness needed to self-adjust the plasma heating power depending on the magnetic energy injection. In the flux ramped-up phase, i.e. in the phase where the applied inductive electric field did not penetrate into the core of the plasma, the J × B compression (pinch effect) was considered to be dominant for heating the FRC. On the other hand, after the applied inductive electric field penetrated into the core region the resistivity of the FRC increased up to 10–20 times larger than the classical spitzer resistivity. This anomalous heating was the most probable cause for sustainment of the high-beta FRC in this phase. A quasi-steady state of the high-beta (volume averaged beta ∼0.6–0.7) FRC for 0.15 ms (∼energy confinement time of conventional FRCs) was achieved by the use of the present low power centre solenoid current drive. This successful result leads us to the next stage steady sustainment experiment of an FRC by increased capacitor bank energy.

Tendency of MHD Forces to Create Localized, Collimated Plasma-filled Flux Tubes & Ion Orbit Instability in a Flux Tube

Electrostatic helicity injection involves the injection of new azimuthal magnetic flux to link the existing axial flux of an open magnetic field. Since magnetic flux is frozen into plasma, this injection of new flux requires the injection of new plasma as well. This associated plasma injection means that helicity injection involves an increase of the density in the flux tube comprised by the initial open magnetic field lines. The injection of plasma and its embedded magnetic flux results in a collimation of the open flux tube when the embedded magnetic flux becomes compressed due to flow stagnation. Plasma injection occurs in the form of jets originating from biased electrodes having plasma sources. These jets can originate from both cathodes and anodes. An ion orbit instability may occur for cathode-originating jets. In cathode-originating jets the ions move opposite to the direction of the conventional current and so experience an anti-pinch force which can be strong enough to overwhelm the usual magnetic force responsible for cyclotron orbit motion.