Plasmoid Propagation Research Articles

Down‐tail mass loss by plasmoids in Jupiter's and Saturn's magnetospheres

AbstractRecent estimates of the plasma mass‐loss rates by the formation and down‐tail propagation of plasmoids observed in the plasma sheet in Jupiter's and Saturn's magnetosphere fall short of inner moon source rates by at least an order of magnitude. Here we argue that on the time scale between large‐scale disconnection events, ~15 h at Jupiter and ~45 h at Saturn, mass‐loaded closed flux tubes will typically have stretched out a few hundred planetary radii down tail at speeds ~100–200 km s−1. Consequently, the “plasmoids” of order ~10 planetary radii in length observed at closer planetary distances represent only a small planetward portion of the overall structure that is disconnected and lost down tail. Plasmoid mass‐loss estimates are then revised upward by around an order of magnitude, becoming comparable to the moon source values. Additional “hidden,” e.g., small‐scale, mass‐loss processes of comparable strength may not then be required. The essentially continuous azimuthally flowing source plasma in the dusk sector is shown to correspond to a plasma sheet layer adjacent to the magnetopause of width typically ~10% of the distance to the magnetopause in that local time sector. This physical picture also provides a simple explanation for the asymmetry in the plasmoid bipolar field signature observed at both Jupiter and Saturn and predicts that the apparent plasmoid length will increase with distance down tail to a limit beyond a few hundred planetary radii where the full ~100–200 planetary radii structures will be observed.

Propagation of plasmoids generated by fast reconnection in the geomagnetic tail

So-called plasmoids are most fundamental signatures of geomagnetic substorms, and precise measurements of magnetic fields have been obtained by in situ satellite observations. Hence, in understanding substorm phenomena, it is essential to clarify the physical mechanism of plasmoid dynamics. The present paper studies on the basis of the spontaneous fast reconnection model how a large-scale plasmoid is generated and propagates in weakly sheared current sheets. It is demonstrated that the basic structure and dynamics of the plasmoid, generated by the fast reconnection, are both qualitatively and quantitatively in good agreement with actual satellite observations. In particular, magnetic field lines inside the generated plasmoid deviate from a helical geometry.

Virtual satellite observations of plasmoids generated by fast reconnection in the geomagnetic tail

Abstract. The present paper studies fundamental features of plasmoid propagation by virtual satellite observations in the simulation box. The plasmoid domain is divided into the plasmoid reconnection region P, where magnetized plasmas with reconnected field lines, heated by dissipation mechanisms of fast reconnection, are accumulated, and the plasmoid core region C, where magnetized plasmas with sheared field lines, initially embedded in the current sheet, is adiabatically compressed. When the virtual satellite is located in a position through which the plasmoid core region passes, it detects distinct changes in quantities at the interface between the regions P and C, where the north-south field component Bz has the bipolar profile and the sheared field component By has the peak value. The observed magnetic field profile is, both quantitatively and qualitatively, in good agreement with the standard one detected by actual satellite observations, although when the satellite location is very close to the X neutral line, where reconnection occurs, the Bz field profile becomes dipolarization-like rather than bipolar. If the satellite detects only the plasmoid region P outside region C, the standard magnetic field profile becomes obscure even if notable plasmoid signatures, such as enhanced plasma temperature and plasma flow, are observed. Unlike the traditional flux rope model based on multiple reconnections, it is demonstrated that the standard magnetic field profile, observed for plasmoids propagating in the geomagnetic tail, is the direct outcome of the single fast reconnection evolution.

Far tail (255RE) fast response to very weak magnetic activity

[1] We present an original study of the dynamical changes measured in the far tail at XGSM ≈ −255 RE, onboard STEREO-B, related to very weak substorm activity (AE < 100 nT). Three weak auroral electrojet perturbations are well correlated with motions of the far tail in which the spacecraft passes from the lobe to the boundary layer or to the magnetosheath. These boundary motions can hardly be related to a plasmoid as a widening of the tail is expected from such a high-pressure structure. Furthermore, for one of the AE enhancements, ground measurement of auroral luminosity and ground magnetic field provided a precise timing of the substorm onset, thus allowing estimation of the propagation speed of the tail disturbance, supposing it is initiated at ∼20 RE in the midtail. The computed velocity, 1800 km/s, much greater than the typical plasmoid propagation speed, implies that the tail disturbance is due to a large-scale wave propagating inside the lobe, initiated inside the inner plasma sheet at substorm onset and linked to current disruption and/or magnetic reconnection.

Three-dimensional evolution of the fast reconnection mechanism in a force-free current sheet

As a sequence of the recent paper on the fast reconnection evolution in a sheared current sheet [M. Ugai, Phys. Plasmas 17, 032313 (2010)], the present paper further studies the three-dimensional fast reconnection evolution in a force-free current sheet system. In general, for the larger sheared field magnitude, the fast reconnection evolution requires the larger spatial scales of the current sheet. For the force-free current sheet system, the critical condition for the fast reconnection evolution is that the current sheet width (extent) in the sheet current direction is about six times larger than its thickness. Once the fast reconnection evolves, the low-β plasma pressure is drastically enhanced in the reconnection outflow region to become comparable with the ambient magnetic pressure. Ahead of the Alfvénic fast reconnection jet, a large-scale plasmoid is formed, where the enhanced plasma pressure is stored. Inside the plasmoid, the sheared field lines are piled up in the form of a core and are significantly wound (or bent) in the sheared field (sheet current) direction because of the oblique plasmoid propagation along the sheared field. The resulting spatial changes in magnetic fields in the plasmoid are found to be in good agreement with the magnetic field signatures usually obtained by satellite observations inside the plasmoid propagating down in the geomagnetic tail.

Three-dimensional evolution of the fast reconnection mechanism in a sheared current sheet

Extending the previous simulation model with the plane symmetry boundaries, the present paper studies the three-dimensional (3D) fast reconnection evolution in the presence of an initial sheared field by employing the axis symmetry boundary conditions. The fast reconnection evolution for the open system, where the reconnection outflow is open to free space, is not significantly influenced by the sheared field, although for the larger magnitude of the sheared field its onset time is more delayed and the fast reconnection process tends to proceed more steadily. In any case, the diffusion region remains to be localized around the X neutral line, and the fast reconnection outflow jet is accelerated to the Alfven velocity by standing slow shocks. The initial sheared field lines are swept away by the reconnection jet, and attached to the jet, a large-scale plasmoid is formed and propagates outward. In the plasmoid, the reconnected sheared field lines are accumulated near the interface between the reconnection jet and the plasmoid, and the sheared field is piled up in the form of a core. The 3D plasmoid propagation is considerably distorted in the direction of the sheared magnetic field since the plasma tends to be accelerated along the sheared field lines.

Solar Origin of the Radio Attributes of a Complex Type III Burst Observed on 11 April 2001

We report here on the solar origin of distinctive radiation characteristics observed for a decametric type III solar radio burst that was associated with a major solar flare and CME on 11 April 2001. The associated decimeter (Ondřejov) and meter (Potsdam) wavelength emissions, as well as the GOES soft X-ray lightcurve, suggest that there were two successive events of energy release and electron acceleration associated with this solar eruption. The Nancay radioheliograph images and additional evidence of plasmoid propagation suggest that the second event of electron acceleration resulted from coronal reconfigurations, likely caused by the erupting CME. These observational analyses provide new insights into the physical origin of the distinguishing characteristics of complex type III-like radio emissions that are typically observed at decameter wavelengths during major solar eruptive events.

The dynamics of plasmoid in asymmetric spontaneous fast reconnection

The spontaneous fast reconnection evolution is studied in asymmetric magnetic field configuration. In particular, it is investigated how shear flow influences in magnetosheath region to the propagation of plasmoid results from magnetic reconnection using two-dimensional magnetohydrodynamic simulations. According to the fast reconnection development, the resulting large-scale plasmoids swell and propagate. Once the plasmoid fully develops, the propagation speed becomes almost constant in both the symmetric and asymmetric magnetic field configuration. An asymmetric plasmoid swells predominantly in the region of a weaker magnetic field and propagates along the field lines. The associated shock structure standing at the plasma boundary is the ordinary slow shock irrespective of the intensity of shear flow. However, velocity of plasmoid is proportional to shear flow velocity.

Radial propagation of Type-I ELMs on JET

The propagation of edge localized modes (ELMs) towards the main chamber could lead to potentially serious consequences in ITER (Federici G et al 2001 Nucl. Fusion 41 1967). This effect was studied in JET by examining the interaction of a large sample (>200) of Type-I ELMs with an array of Langmuir probes on the outboard limiter. High clearance discharges were used with a separatrix to wall distance of 8–18 cm. The average ELM duration was measured as ∼ 200 ± 50 µs, the average radial propagation velocity of the ELM plasmoid in the scrape-off layer as ⟨v⊥⟩ ∼ 0.45 ± 0.1 km s−1 or as a fraction of the sound speed, ⟨v⊥/cs⟩ ∼ 0.2%, and its diffusion coefficient, D⊥, as 500 ± 100 m2 s−1—a significant increase over inter-ELM levels. The above velocities are in good agreement with the lower (∥ loss) limit of the sheath-limited model of plasmoid propagation (Krasheninnikov S I 2001 Phys. Lett. A 283 368, Krasheninnikov S I et al 2002 29th EPS Conf. on Controlled Fusion and Plasma Physics (Montreux, Switzerland)).

Basic Physical Mechanism of Fast Reconnection Evolution in Space Plasmas

Large dissipative events, such as solar flares and geomagnetic substorms, may result from sudden onset of fast (explosive) magnetic reconnection. Hence, it is a long-standing problem to find the physical mechanism that makes magnetic reconnection explosive; in particular, how can the fast magnetic reconnection explosively evolve in space plasmas? In this respect, we have proposed the spontaneous fast reconnection model as a nonlinear instability that grows by the positive feedback between plasma microphysics (anomalous resistivity) and macrophysics (global reconnection flow). On the basis of MHD simulations, we demonstrate for a variety of physical situations that the fast reconnection mechanism involving slow shocks in fact evolves explosively as a nonlinear instability and is sustained quasi-steadily on the nonlinear saturation phase. Also, distinct plasma processes, such as large-scale plasmoid propagation, magnetic loop development and loop-top heating, and asymmetric fast reconnection evolution, directly result from the spontaneous fast reconnection model. Obviously, MHD simulations are very useful in understanding the basic physics of explosive fast reconnection evolution in space plasmas. However, they cannot treat the details of microphysics near an X neutral point, which should be precisely studied in the coming 21st century.

Impulsive plasmoid penetration of a tangential discontinuity: Two‐dimensional ideal and Hall magnetohydrodynamics

Impulsive plasmoid penetration of a tangential discontinuity (e.g., the magnetopause) is studied using two‐dimensional ideal and Hall magnetohydro‐dynamics. The model assumes a unidirectional magnetic field and describes the plasma and field dynamics transverse to the field; this is an idealized model and not typical of the magnetopause. Two magnetic field configurations are studied: the parallel field case where the magnetic fields in the magnetosheath and magnetosphere are in the same direction and the antiparallel field case where they are in opposite directions. The evolution of the plasmoid is symmetric about its propagation direction in ideal MHD. One new ideal MHD result is that after the plasmoid penetrates the discontinuity it undergoes vortex shedding. The Hall MHD results are similar to those obtained by Savoini et al. [1994]. The major similarity is that the plasmoid penetration process is asymmetric. The Hall antiparallel field case, although asymmetric, evolves very much like the ideal MHD case. However, the Hall parallel field case evolves much differently from the ideal MHD case. The plasmoid undergoes a substantial deformation in the direction orthogonal to the propagation direction and does not penetrate as far into the magnetosphere. We suggest that the Hall term can be an important mechanism to provide asymmetric plasmoid propagation through the discontinuity and that Hall MHD can capture important macroscopic effects observed in hybrid simulations that are not described by ideal MHD.

Radio and X-Ray Variability of the Galactic Superluminal Source GRS 1915+105

We report results of radio and hard X-ray monitoring observations of the Galactic superluminal X-ray source GRS 1915+105 carried out with the Green Bank Interferometer and the Burst and Transient Source Experiment during the period 1994 September through 1996 March. Both the radio and the hard X-ray light curves show a complex transient behavior. The radio emission monitored at 2.25 and 8.3 GHz is correlated with episodes of enhanced hard X-ray emission. A phenomenological classification of the radio emission indicates two distinct emission modes: plateau and flaring. Plateau radio emission is in general optically thick, with a flat-topped light curve showing a rapid onset and decrease of the flux density. The radio flaring state shows large radio flares that can increase in flux density by 2 orders of magnitude in less than 18 hr, followed by an optically thin exponential decay. These observed large radio flares are consistent with external propagation of plasmoids emitting synchrotron radiation. We comment on the significance of these results, and suggest a scenario for modeling the multiwavelength behavior of GRS 1915+105.

Computer studies on plasmoid dynamics associated with the spontaneous fast reconnection mechanism

The spontaneous fast reconnection model is applied to the plasmoid dynamics, and computer simulations are performed for a wide range of parameters. According to the fast reconnection development, the resulting strong (Alfvénic) plasma jet drives a large-scale plasmoid to swell and propagate. Once the plasmoid fully develops, the propagation speed Vp becomes almost constant. It is the J×B force, not the pressure-gradient force, that plays the dominant role on the plasmoid propagation. It is estimated that Vp∼0.8VA l0, where VA l0 is the Alfvén velocity measured in the magnetic field region ahead of the plasmoid. Along the backward-half plasmoid boundary a strong slow (almost switch-off) shock is formed, whereas along the forward-half boundary a rather weak slow shock stands. The plasma pressure is largely enhanced in the middle of the plasmoid, and the magnetic energy just outside the plasmoid is notably enhanced in the forward half because of the generator effect and is then distinctly reduced in the backward half by the strong motor effect. For the uniform resistivity model, any distinct plasmoid cannot be set up. It is argued that the spontaneous fast reconnection mechanism should be most applicable to catastrophic events observed in space plasmas.

Plasmoid propagation in a transverse magnetic field and in a magnetized plasma

The propagation of plasmoids (neutralized ion beams) in a vacuum transverse-magnetic field has been studied in the University of California, Irvine laboratory for several years [Phys. Fluids 24, 739 (1981); 25, 730, 2353 (1982); 26, 2276 (1983); J. Appl. Phys. 64, 73 (1988)]. These experiments have confirmed that the plasmoid propagates by the E×B drift in a low beta and high beta plasmoid beam (0.01&amp;lt;β&amp;lt;300), where β is the ratio of beam kinetic energy to magnetic field energy. The polarization electric field E arises from the opposite deflection of the plasmoid ions and electrons, because of the Lorentz force, and allows the plasmoid to propagate undeflected at essentially the initial plasmoid velocity. In these experiments, plasmoids (150 keV, 5 kA, 50–100 A/cm2, 1 μ sec) were injected into transverse fields of Bt=0–400 G. Anomalously fast penetration of the transverse magnetic field has been observed as in the ‘‘Porcupine’’ experiments [J. Geophys. Res. 91, 10,183 (1987)]. The most recent experiments are aimed at studying the plasmoid propagation dynamics and losses in the presence of a background, magnetized plasma which is intended to short the induced polarization electric field and stop the beam. Background plasma was generated by TiH4 plasma guns fired along Bt to produce a plasma density, np =1012 −1014 cm−3 . Preliminary results indicate that the beam propagation losses increase with the background plasma density; compared to vacuum propagation, roughly a 50% reduction in ion current density was noted 70 cm downstream from the anode for np∼1013 cm−3 . Principal diagnostics include magnetically insulated Faraday cups, floating potential probes, calorimeters, microwave interferometer, and thermal-witness paper.

Comments on “Production and Propagation of Plasmoids in a Nonlinear Alfvén Wave”

Comments on “Production and Propagation of Plasmoids in a Nonlinear Alfvén Wave”

Production and Propagation of Plasmoids in a Nonlinear Alfvén Wave

A variational theory of hydromagnetic dynamic equilibria is applied to plasmoids produced in a conical theta pinch immersed in a magnetic guide field. The solutions correspond to nonlinear Alfvén waves which trap and transport plasma.

Propagation of Plasmoids at High Pressures

Propagation of Plasmoids at High Pressures