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Articoli di riviste sul tema "Plasmoids"

Autore: Grafiati

Pubblicato: 28 marzo 2023

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1

Christie, I. M., M. Petropoulou, L. Sironi e D. Giannios. "Interplasmoid Compton scattering and the Compton dominance of BL Lacs". Monthly Notices of the Royal Astronomical Society 492, n. 1 (9 dicembre 2019): 549–55. http://dx.doi.org/10.1093/mnras/stz3265.

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ABSTRACT Blazar emission models based on magnetic reconnection succeed in reproducing many observed spectral and temporal features, including the short-duration luminous flaring events. Plasmoids, a self-consistent by-product of the tearing instability in the reconnection layer, can be the main source of blazar emission. Kinetic simulations of relativistic reconnection have demonstrated that plasmoids are characterized by rough energy equipartition between their radiating particles and magnetic fields. This is the main reason behind the apparent shortcoming of plasmoid-dominated emission models to explain the observed Compton ratios of BL Lac objects. Here, we demonstrate that the radiative interactions among plasmoids, which have been neglected so far, can assist in alleviating this contradiction. We show that photons emitted by large, slow-moving plasmoids can be a potentially important source of soft photons to be then upscattered, via inverse Compton, by small fast-moving, neighbouring plasmoids. This interplasmoid Compton scattering process can naturally occur throughout the reconnection layer, imprinting itself as an increase in the observed Compton ratios from those short and luminous plasmoid-powered flares within BL Lac sources, while maintaining energy equipartition between radiating particles and magnetic fields.

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Suzuki, Y., T. H. Watanabe, A. Kageyama, T. Sato e T. Hayashi. "Three-Dimensional Simulation Study of Plasmoid Injection into Magnetized Plasma". Symposium - International Astronomical Union 188 (1998): 209–10. http://dx.doi.org/10.1017/s0074180900114780.

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Resent observations suggest that, during solar flares, plasmoids are injected into the interplanetary medium (Stewart et al., 1982). It has also been pointed out that solar wind irregularities modeled as plasmoids are penetrated into the magnetosphere (Lemaire, 1977). These plasmoid injections are considered to be an important process because they transfer mass, momentum, and energy into such magnetized plasma regions. Our objective is to investigate the dynamics of a plasmoid, which is injected into a magnetized plasma region and to reveal mechanisms to transfer them. To achieve this, we carried out three-dimensional magnetohydrodynamic (MHD) simulations.

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3

Honkonen, I., M. Palmroth, T. I. Pulkkinen, P. Janhunen e A. Aikio. "On large plasmoid formation in a global magnetohydrodynamic simulation". Annales Geophysicae 29, n. 1 (14 gennaio 2011): 167–79. http://dx.doi.org/10.5194/angeo-29-167-2011.

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Abstract. We investigate plasmoid formation in the magnetotail using the global magnetohydrodynamic (MHD) simulation GUMICS-4. Here a plasmoid implies a major reconfiguration of the magnetotail where a part of the tail plasma sheet is ejected downstream, in contrast to small Earthward-propagating plasmoids. We define a plasmoid based solely on the structure of the closed (connected to the Earth at both ends) magnetic field line region. In this definition a plasmoid is partly separated from the ordinary closed field line region by lobe field lines or interplanetary field lines resulting from lobe reconnection. We simulate an event that occurred on 18 February 2004 during which four intensifications of the auroral electroject (AE) index occurred in 8 h. Plasmoids form in the simulation for two of the four AE intensifications. Each plasmoid forms as a result of two consecutive large and fast rotations of the interplanetary magnetic field (IMF). In both cases the IMF rotates 180 degrees at 10 degrees per minute, first from southward to northward and some 15 min later from northward to southward. The other two AE intencifications however are not associated with a plasmoid formation. A plasmoid does not form if either the IMF rotation speed or the angular change of the rotation are small. We also present an operational definition for these fully connected plasmoids that enables their automatic detection in simulations. Finally, we show mappings of the plasmoid footpoints in the ionosphere, where they perturb the polar cap boundary in both hemispheres.

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Patel, Ritesh, Vaibhav Pant, Kalugodu Chandrashekhar e Dipankar Banerjee. "A statistical study of plasmoids associated with a post-CME current sheet". Astronomy & Astrophysics 644 (dicembre 2020): A158. http://dx.doi.org/10.1051/0004-6361/202039000.

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Context. Coronal mass ejections (CMEs) are often observed to be accompanied by flare, current sheets, and plasmoids/plasma blobs. 2D and 3D numerical simulations and observations reported plasmoids moving upward as well as downward along the current sheet. Aims. We aim to investigate the properties of plasmoids observed in the current sheet formed after an X-8.3 flare and followed by a fast CME eruption on September 10, 2017 using extreme-ultraviolet (EUV) and white-light coronagraph images. The main goal is to understand the evolution of plasmoids in different spatio-temporal scales using existing ground- and space-based instruments. Methods. We identified the plasmoids manually and tracked them along the current sheet in the successive images of Atmospheric Imaging Assembly (AIA) taken at the 131 Å pass band and in running difference images of the white-light coronagraphs, K-Cor and LASCO/C2. The location and size of the plasmoids in each image were recorded and analyzed, covering the current sheet from the inner to outer corona. Results. We find that the observed current sheet has an Alfvén Mach number of 0.018−0.35. The fast reconnection is also accompanied by plasmoids moving upward and downward. We identified 20 downward-moving and 16 upward-moving plasmoids using AIA 131 Å images. In white-light coronagraph images, only upward-moving plasmoids are observed. Our analysis shows that the downward-moving plasmoids have an average width of 5.92 Mm, whereas upward-moving blobs have an average size of 5.65 Mm in the AIA field of view (FOV). The upward-moving plasmoids, when observed in the white-light images, have an average width of 64 Mm in the K-Cor, which evolves to a mean width of 510 Mm in the LASCO/C2 FOV. Upon tracking the plasmoids in successive images, we find that downward- and upward-moving plasmoids have average speeds of ∼272 km s−1 and ∼191 km s−1, respectively in the EUV channels of observation. The average speed of plasmoids increases to ∼671 km s−1 and ∼1080 km s−1 in the K-Cor and LASCO/C2 FOVs, respectively, implying that the plasmoids become super-Alfvénic when they propagate outward. The downward-moving plasmoids show an acceleration in the range of −11 km s−1 to over 8 km s−1. We also find that the null point of the current sheet is located at ≈1.15 R⊙, where bidirectional plasmoid motion is observed. Conclusions. The width distribution of plasmoids formed during the reconnection process is governed by a power law with an index of −1.12. Unlike previous studies, there is no difference in trend for small- and large-scale plasmoids. The evolution of width W of the plasmoids moving at an average speed V along the current sheet is governed by an empirical relation: V = 115.69W0.37. The presence of accelerating plasmoids near the neutral point indicates a longer diffusion region as predicted by MHD models.

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5

Lemaire, J. "Plasmoid motion across a tangential discontinuity (with application to the magnetopause)". Journal of Plasma Physics 33, n. 3 (giugno 1985): 425–36. http://dx.doi.org/10.1017/s0022377800002592.

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The motion of a plasmoid (plasma-field entity) across an inhomogeneous magnetic field distribution of which the direction and strength change along the penetration trajectory has been studied. The bulk velocity decreases when the plasma element penetrates into a region of increasing magnetic field. The critical magnetic field intensity where a plasmoid is stopped or deflected is found to be the same critical field as that which has been observed in laboratory experiments for a non-rotating B-field distribution. The polarization electric field induced inside a moving plasma element has been determined for both low-β and high-β plasmoids. The momentum density vector of a plasmoid is deflected in the – B × ∇B and – B × (B. ∇)B directions as it penetrates into an inhomogeneous B-field distribution. This kinetic model has been applied to the impulsive penetration of solar wind plasma irregularities impinging on the earth's geomagnetic field with an excess momentum density. As a consequence of impulsive penetration, a plasma boundary layer is formed where the intruding plasmoids are deflected eastward. Magnetospheric plasma is dragged in the direction parallel to the flanks of the average magnetopause surface. Diamagnetic effects of these impulsively penetrating plasmoids into the magnetosphere are also briefly discussed.

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Cerutti, Benoît, e Gwenael Giacinti. "Formation of giant plasmoids at the pulsar wind termination shock: A possible origin of the inner-ring knots in the Crab Nebula". Astronomy & Astrophysics 656 (dicembre 2021): A91. http://dx.doi.org/10.1051/0004-6361/202142178.

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Context. Nearby pulsar wind nebulae exhibit complex morphological features: jets, torus, arcs, and knots. These structures are well captured and understood in the scope of global magnetohydrodynamic models. However, the origin of knots in the inner radius of the Crab Nebula remains elusive. Aims. In this work, we investigate the dynamics of the shock front and downstream flow with a special emphasis on the reconnecting equatorial current sheet. We examine whether giant plasmoids produced in the reconnection process could be good candidates for the knots. Methods. To this end, we perform large semi-global three-dimensional particle-in-cell simulations in a spherical geometry. The hierarchical merging plasmoid model is used to extrapolate numerical results to pulsar wind nebula scales. Results. The shocked material collapses into the midplane, forming and feeding a large-scale, but thin, ring-like current layer. The sheet breaks up into a dynamical chain of merging plasmoids, reminiscent of three-dimensional reconnection. Plasmoids grow to a macroscopic size. The final number of plasmoids predicted is solely governed by the inverse of the dimensionless reconnection rate. Conclusions. The formation of giant plasmoids is a robust feature of pulsar wind termination shocks. They provide a natural explanation for the inner-ring knots in the Crab Nebula, provided that the nebula is highly magnetized.

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7

Markidis, S., P. Henri, G. Lapenta, A. Divin, M. V. Goldman, D. Newman e S. Eriksson. "Collisionless magnetic reconnection in a plasmoid chain". Nonlinear Processes in Geophysics 19, n. 1 (27 febbraio 2012): 145–53. http://dx.doi.org/10.5194/npg-19-145-2012.

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Abstract. The kinetic features of plasmoid chain formation and evolution are investigated by two dimensional Particle-in-Cell simulations. Magnetic reconnection is initiated in multiple X points by the tearing instability. Plasmoids form and grow in size by continuously coalescing. Each chain plasmoid exhibits a strong out-of plane core magnetic field and an out-of-plane electron current that drives the coalescing process. The disappearance of the X points in the coalescence process are due to anti-reconnection, a magnetic reconnection where the plasma inflow and outflow are reversed with respect to the original reconnection flow pattern. Anti-reconnection is characterized by the Hall magnetic field quadrupole signature. Two new kinetic features, not reported by previous studies of plasmoid chain evolution, are here revealed. First, intense electric fields develop in-plane normally to the separatrices and drive the ion dynamics in the plasmoids. Second, several bipolar electric field structures are localized in proximity of the plasmoid chain. The analysis of the electron distribution function and phase space reveals the presence of counter-streaming electron beams, unstable to the two stream instability, and phase space electron holes along the reconnection separatrices.

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8

Dubowsky, Scott E., Amber N. Rose, Nick G. Glumac e Benjamin J. McCall. "Electrical Properties of Reversed-Polarity Ball Plasmoid Discharges". Plasma 3, n. 3 (29 giugno 2020): 92–102. http://dx.doi.org/10.3390/plasma3030008.

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Ball plasmoid discharges are a unique type of atmospheric-pressure plasma discharge with a lifetime on the order of a hundred milliseconds without attachment to a power source. These discharges are generated by a moderate current pulse over the surface of an aqueous electrolyte, and some consider the spherical plasmoid that results to bear some resemblance to ball lightning. This article presents the first analysis of the electrical properties of ball plasmoid discharges in a reversed-polarity configuration, i.e., with the central electrode serving as the anode rather than as the cathode. These experiments demonstrate that ball plasmoids can indeed be generated with either electrode polarity with similar observable properties. These results are contrary to what has previously been discussed in the literature and raise additional questions regarding formation mechanisms of ball plasmoids. Analysis of images and electrical measurements collected at various discharge energies show that two distinct processes occur during discharges with our circuitry and in this reversed-polarity configuration: the formation of spark channels between the anode and electrolyte, and the generation of streamers and a jet from the surface of the anode.

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Dvornikov, M. "Stable Langmuir solitons in plasma with diatomic ions". Nonlinear Processes in Geophysics 20, n. 4 (13 agosto 2013): 581–88. http://dx.doi.org/10.5194/npg-20-581-2013.

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Abstract. We study stable axially and spherically symmetric spatial solitons in plasma with diatomic ions. The stability of a soliton against collapse is provided by the interaction of induced electric dipole moments of ions with the rapidly oscillating electric field of a plasmoid. We derive the new cubic-quintic nonlinear Schrödinger equation, which governs the soliton dynamics and numerically solve it. Then we discuss the possibility of implementation of such plasmoids in realistic atmospheric plasma. In particular, we suggest that spherically symmetric Langmuir solitons, described in the present work, can be excited at the formation stage of long-lived atmospheric plasma structures. The implication of our model for the interpretation of the results of experiments for the plasmoids generation is discussed.

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10

Nathanail, Antonios, Christian M. Fromm, Oliver Porth, Hector Olivares, Ziri Younsi, Yosuke Mizuno e Luciano Rezzolla. "Plasmoid formation in global GRMHD simulations and AGN flares". Monthly Notices of the Royal Astronomical Society 495, n. 2 (23 maggio 2020): 1549–65. http://dx.doi.org/10.1093/mnras/staa1165.

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ABSTRACT One of the main dissipation processes acting on all scales in relativistic jets is thought to be governed by magnetic reconnection. Such dissipation processes have been studied in idealized environments, such as reconnection layers, which evolve in merging islands and lead to the production of ‘plasmoids’, ultimately resulting in efficient particle acceleration. In accretion flows on to black holes, reconnection layers can be developed and destroyed rapidly during the turbulent evolution of the flow. We present a series of two-dimensional general-relativistic magnetohydrodynamic simulations of tori accreting on to rotating black holes focusing our attention on the formation and evolution of current sheets. Initially, the tori are endowed with a poloidal magnetic field having a multiloop structure along the radial direction and with an alternating polarity. During reconnection processes, plasmoids and plasmoid chains are developed leading to a flaring activity and hence to a variable electromagnetic luminosity. We describe the methods developed to track automatically the plasmoids that are generated and ejected during the simulation, contrasting the behaviour of multiloop initial data with that encountered in typical simulations of accreting black holes having initial dipolar field composed of one loop only. Finally, we discuss the implications that our results have on the variability to be expected in accreting supermassive black holes.

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Gou, Tingyu, Rui Liu, Bernhard Kliem, Yuming Wang e Astrid M. Veronig. "The birth of a coronal mass ejection". Science Advances 5, n. 3 (marzo 2019): eaau7004. http://dx.doi.org/10.1126/sciadv.aau7004.

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The Sun’s atmosphere is frequently disrupted by coronal mass ejections (CMEs), coupled with flares and energetic particles. The coupling is usually attributed to magnetic reconnection at a vertical current sheet connecting the flare and CME, with the latter embedding a helical magnetic structure known as flux rope. However, both the origin of flux ropes and their nascent paths toward eruption remain elusive. Here, we present an observation of how a stellar-sized CME bubble evolves continuously from plasmoids, mini flux ropes that are barely resolved, within half an hour. The eruption initiates when plasmoids springing from a vertical current sheet merge into a leading plasmoid, which rises at increasing speeds and expands impulsively into the CME bubble, producing hard x-ray bursts simultaneously. This observation illuminates a complete CME evolutionary path capable of accommodating a wide variety of plasma phenomena by bridging the gap between microscale and macroscale dynamics.

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Belehaki, A., R. W. McEntire, S. Kokubun e T. Yamamoto. "Magnetotail response during a strong substorm as observed by GEOTAIL in the distant tail". Annales Geophysicae 16, n. 5 (31 maggio 1998): 528–41. http://dx.doi.org/10.1007/s00585-998-0528-5.

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Abstract. Simultaneous energetic particle and magnetic field observations from the GEOTAIL spacecraft in the distant tail (XGSM≈ –150 Re) have been analysed to study the response of the Earth's magnetotail during a strong substorm (AE ≤ 680 nT). At geosynchronous altitude, LANL spacecraft recorded three electron injections between 0030 UT and 0130 UT, which correspond to onsets observed on the ground at Kiruna Ground Observatory. The Earth's magnetotail responded to this substorm with the ejection of five plasmoids, whose size decreases from one plasmoid to the next. Since the type of magnetic structure detected by a spacecraft residing the lobes, depends on the Z extent of the structure passing underneath the spacecraft, GEOTAIL is first engulfed by a plasmoid structure; six minutes later it detects a boundary layer plasmoid (BLP) and finally at the recovery phase of the substorm GEOTAIL observes three travelling compression regions (TCRs). The time-of-flight (TOF) speed of these magnetic structures was estimated to range between 510 km/s and 620 km/s. The length of these individual plasmoids was calculated to be between 28 Re and 56 Re. The principal axis analysis performed on the magnetic field during the TCR encountered, has confirmed that GEOTAIL observed a 2-D perturbation in the X-Z plane due to the passage of a plasmoid underneath. The first large plasmoid that engulfed GEOTAIL was much more complicated in nature probably due to the external, variable draped field lines associated with high beta plasma sheet and the PSBL flux tubes surrounding the plasmoid. From the analysis of the energetic particle angular distribution, evidence was found that ions were accelerated from the distant X-line at the onset of the burst associated with the first magnetic structure. Key words. Magnetospheric physics (magnetospheric configuration and dynamics; magnetotail).

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AHMAD, Nisar, Ping ZHU, Ahmad ALI e Shiyong ZENG. "Viscous effects on plasmoid formation from nonlinear resistive tearing growth in a Harris sheet". Plasma Science and Technology 24, n. 1 (23 novembre 2021): 015103. http://dx.doi.org/10.1088/2058-6272/ac3563.

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Abstract In this work, the evolution of a highly unstable m = 1 resistive tearing mode, leading to plasmoid formation in a Harris sheet, is studied in the framework of full MHD model using the Non-Ideal Magnetohydrodynamics with Rotation, Open Discussion simulation. Following the initial nonlinear growth of the primary m = 1 island, the X-point develops into a secondary elongated current sheet that eventually breaks into plasmoids. Two distinctive viscous regimes are found for the plasmoid formation and saturation. In the low viscosity regime (i.e. P r ≲ 1), the plasmoid width increases sharply with viscosity, whereas in the viscosity dominant regime (i.e. P r ≳ 1), the plasmoid size gradually decreases with viscosity. Such a finding quantifies the role of viscosity in modulating the plasmoid formation process through its effects on the plasma flow and the reconnection itself.

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Ugai, M. "Virtual satellite observations of plasmoids generated by fast reconnection in the geomagnetic tail". Annales Geophysicae 29, n. 8 (23 agosto 2011): 1411–22. http://dx.doi.org/10.5194/angeo-29-1411-2011.

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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.

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Gunell, H., G. Stenberg Wieser, M. Mella, R. Maggiolo, H. Nilsson, F. Darrouzet, M. Hamrin et al. "Waves in high-speed plasmoids in the magnetosheath and at the magnetopause". Annales Geophysicae 32, n. 8 (22 agosto 2014): 991–1009. http://dx.doi.org/10.5194/angeo-32-991-2014.

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Abstract. Plasmoids, defined here as plasma entities with a higher anti-sunward velocity component than the surrounding plasma, have been observed in the magnetosheath in recent years. During the month of March 2007 the Cluster spacecraft crossed the magnetopause near the subsolar point 13 times. Plasmoids with larger velocities than the surrounding magnetosheath were found on seven of these 13 occasions. The plasmoids approach the magnetopause and interact with it. Both whistler mode waves and waves in the lower hybrid frequency range appear in these plasmoids, and the energy density of the waves inside the plasmoids is higher than the average wave energy density in the magnetosheath. When the spacecraft are in the magnetosphere, Alfvénic waves are observed. Cold ions of ionospheric origin are seen in connection with these waves, when the wave electric and magnetic fields combine with the Earth's dc magnetic field to yield an E × B/B2 drift speed that is large enough to give the ions energies above the detection threshold.

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Lu, Lei, Li Feng, Alexander Warmuth, Astrid M. Veronig, Jing Huang, Siming Liu, Weiqun Gan, Zongjun Ning, Beili Ying e Guannan Gao. "Observational Signatures of Tearing Instability in the Current Sheet of a Solar Flare". Astrophysical Journal Letters 924, n. 1 (1 gennaio 2022): L7. http://dx.doi.org/10.3847/2041-8213/ac42c6.

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Abstract Magnetic reconnection is a fundamental physical process converting magnetic energy into not only plasma energy but also particle energy in various astrophysical phenomena. In this Letter, we show a unique data set of a solar flare where various plasmoids were formed by a continually stretched current sheet. Extreme ultraviolet images captured reconnection inflows, outflows, and particularly the recurring plasma blobs (plasmoids). X-ray images reveal nonthermal emission sources at the lower end of the current sheet, presumably as large plasmoids with a sufficiently amount of energetic electrons trapped in them. In the radio domain, an upward, slowly drifting pulsation structure, followed by a rare pair of oppositely drifting structures, was observed. These structures are supposed to map the evolution of the primary and the secondary plasmoids formed in the current sheet. Our results on plasmoids at different locations and scales shed important light on the dynamics, plasma heating, particle acceleration, and transport processes in the turbulent current sheet and provide observational evidence for the cascading magnetic reconnection process.

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Nagai, T., H. Tsunakawa, H. Shibuya, F. Takahashi, H. Shimizu, M. Matsushima, M. N. Nishino et al. "Plasmoid formation for multiple onset substorms: observations of the Japanese Lunar Mission "Kaguya"". Annales Geophysicae 27, n. 1 (6 gennaio 2009): 59–64. http://dx.doi.org/10.5194/angeo-27-59-2009.

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Abstract. The Japanese Lunar Mission "Kaguya" carried out its first magnetic field and plasma measurements in the Earth's magnetotail on 22 December 2007. Fortuitously, three well-defined multiple onset substoms took place. Kaguya was located in the premidnight magnetotail at radial distances of 56 RE and observed plasmoids and/or traveling compression regions (TCRs). Although the present study is based on limited data sets, important issues on multiple onset substorms can be examined. Each onset in a series of onsets releases a plasmoid, and magnetic reconnection likely proceeds to tail lobe field lines for each onset. Since the duration of each plasmoid is less than 5 min, these observations imply that magnetic reconnection for each onset can develop fully to the tail lobe field lines and be quenched within this timescale.

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Xie, Xiaoyan, Zhixing Mei, Chengcai Shen, Qiangwei Cai, Jing Ye, Katharine K. Reeves, Ilia I. Roussev e Jun Lin. "Numerical experiments on dynamic evolution of a CME-flare current sheet". Monthly Notices of the Royal Astronomical Society 509, n. 1 (19 ottobre 2021): 406–20. http://dx.doi.org/10.1093/mnras/stab2954.

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ABSTRACT In this paper, we performed magnetohydrodynamics numerical experiments to look into the dynamic behaviour of the current sheet (CS) between the coronal mass ejection (CME) and the associated solar flare, especially the CS oscillation and plasmoid motions in coronal conditions. During the evolution, the disrupting magnetic configuration becomes asymmetric first in the buffer region at the bottom of the CME bubble. The Rayleigh−Taylor instability in the buffer region and the deflected motion of the plasma driven by the termination shock at the bottom of the CME bubble cause the buffer region to oscillate around the y-axis. The local oscillation propagates downwards through the CS, prompting an overall CS oscillation. As the buffer region grows, the oscillation period becomes longer, increasing from about 30 s to about 16 min. Meanwhile, there is another separated oscillation with a period between 0.25 and 1.5 min in the cusp region of the flare generated by velocity shearing. The tearing mode instability yields formations of plasmoids inside the CS. The motions of all the plasmoids observed in the experiment accelerate, which implies that the large-scale CME/flare CS itself in the true eruptive event is filled with the diffusion region according the the standard theory of magnetic reconnection.

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W Hones Jr, Edward. "Magnetic Reconnection in the Earth's Magnetotail". Australian Journal of Physics 38, n. 6 (1985): 981. http://dx.doi.org/10.1071/ph850981.

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Over the past few years satellite observations of the plasma sheet in the Earth's magnetotail during magnetospheric substorms have established beyond reasonable doubt that magnetic reconnection occurs in the magnetotail and that it plays a central role in the substorm process. The features seen at Earth by which substorms were originally identified (e.g. the auroras and geomagnetic disturbances) are simply superficial manifestations of a more fundamental physical process-the magnetosphere divesting itself of stored energy and plasma that was acquired earlier from the solar wind. It does so by shedding a part of its plasma sheet. This is accomplished by magnetic reconnection near the Earth that severs the plasma sheet, forming a plasmoid that flows out of the tail and that is lost to the solar wind. Recognition of the existence of plasmoids and our developing understanding of them have been important elements in confirming the occurrence of reconnection in the magnetosphere. In an analogous way, the best evidence for the occurrence of reconnection on the Sun has come from observations of closed magnetic configurations (plasmoids) in the solar wind and in the corona. But while magnetic reconnection is certainly the key ingredient in solar flares and substorms, analogies between them should not be carried too far, because there are basic differences in the environments in which they prevail and in the physical procesSes that lead to their occurrence.

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Hill, T. W., M. F. Thomsen, M. G. Henderson, R. L. Tokar, A. J. Coates, H. J. McAndrews, G. R. Lewis et al. "Plasmoids in Saturn's magnetotail". Journal of Geophysical Research: Space Physics 113, A1 (gennaio 2008): n/a. http://dx.doi.org/10.1029/2007ja012626.

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Ortuño-Macías, José, e Krzysztof Nalewajko. "Radiative kinetic simulations of steady-state relativistic plasmoid magnetic reconnection". Monthly Notices of the Royal Astronomical Society 497, n. 2 (3 luglio 2020): 1365–81. http://dx.doi.org/10.1093/mnras/staa1899.

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ABSTRACT We present the results of two-dimensional particle-in-cell (PIC) simulations of relativistic magnetic reconnection (RMR) in electron–positron plasma, including the dynamical influence of the synchrotron radiation process, and integrating the observable emission signatures. The simulations are initiated with a single Harris current layer with a central gap that triggers the RMR process. We achieve a steady-state reconnection with unrestricted outflows by means of open boundary conditions. The radiative cooling efficiency is regulated by the choice of initial plasma temperature Θ. We explore different values of Θ and of the background magnetization σ0. Throughout the simulations, plasmoids are generated in the central region of the layer, and they evolve at different rates, achieving a wide range of sizes. The gaps between plasmoids are filled by smooth relativistic outflows called minijets, whose contribution to the observed radiation is very limited due to their low-particle densities. Small-sized plasmoids are rapidly accelerated; however, they have lower contributions to the observed emission, despite stronger relativistic beaming. Large-sized plasmoids are slow but produce most of the observed synchrotron emission, with major part of their radiation produced within the central cores, the density of which is enhanced by radiative cooling. Synchrotron light curves show rapid bright flares that can be identified as originating from mergers between small/fast plasmoids and large/slow targets moving in the same direction. In the high-magnetization case, the accelerated particles form a broken power-law energy distribution with a soft tail produced by particles accelerated in the minijets.

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22

Hoshino, M. "Small scale plasmoids in the post-plasmoid plasma sheet: Origin of MHD turbulence?" Advances in Space Research 25, n. 7-8 (gennaio 2000): 1685–88. http://dx.doi.org/10.1016/s0273-1177(99)00684-5.

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23

Moldwin, Mark B., e W. Jeffrey Hughes. "Geomagnetic substorm association of plasmoids". Journal of Geophysical Research: Space Physics 98, A1 (1 gennaio 1993): 81–88. http://dx.doi.org/10.1029/92ja02153.

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24

Moldwin, Mark B., e W. Jeffrey Hughes. "Plasmoids as magnetic flux ropes". Journal of Geophysical Research: Space Physics 96, A8 (1 agosto 1991): 14051–64. http://dx.doi.org/10.1029/91ja01167.

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25

Nagai, T., R. Nakamura, T. Mukai, T. Yamamoto, A. Nishida e S. Kokubun. "Substorms, tail flows and plasmoids". Advances in Space Research 20, n. 4-5 (gennaio 1997): 961–71. http://dx.doi.org/10.1016/s0273-1177(97)00504-8.

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26

Pothiraja, Ramasamy, Nikita Bibinov e Peter Awakowicz. "Plasmoids for etching and deposition". Journal of Physics D: Applied Physics 47, n. 45 (23 ottobre 2014): 455203. http://dx.doi.org/10.1088/0022-3727/47/45/455203.

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27

Wells, Daniel R., e Lawrence Carl Hawkins. "Containment forces in low energy states of plasmoids". Journal of Plasma Physics 38, n. 2 (ottobre 1987): 263–74. http://dx.doi.org/10.1017/s0022377800012563.

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The application of Hamilton's principle to the problem of the determination of the structure of low free energy state plasmoids is discussed. It is shown that Clebsch representations of the vector fields and representations involving side conditions on the functional result in the same sets of Euler–Lagrange equations. The relationship of these representations to the problem of containment forces in vortex structures (plasmoids) is considered. It is demonstrated that the lowest free energy state of an incompressible plasma is always Lorentz force and Magnus force free. For a compressible plasma obeying the adiabatic gas laws, the Magnus force is finite. Introduction of conservation of angular momentum as an additional side condition also results in finite containment forces.

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28

Yu, Q., S. Günter e K. Lackner. "Formation of plasmoids during sawtooth crashes". Nuclear Fusion 54, n. 7 (1 maggio 2014): 072005. http://dx.doi.org/10.1088/0029-5515/54/7/072005.

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29

Silbergleit, V. M., M. M. Zossi de Artigas e J. R. Manzano. "Energy dissipation in substorms: plasmoids ejection". Journal of Atmospheric and Solar-Terrestrial Physics 59, n. 11 (luglio 1997): 1355–58. http://dx.doi.org/10.1016/s1364-6826(96)00108-3.

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30

Lau, Yun-Tung, e John M. Finn. "Three-dimensional kinematic reconnection of plasmoids". Astrophysical Journal 366 (gennaio 1991): 577. http://dx.doi.org/10.1086/169593.

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31

Mikikian, Maxime, Hagop Tawidian e Thomas Lecas. "Unstable Plasmoids in Dusty Plasma Experiments". IEEE Transactions on Plasma Science 42, n. 10 (ottobre 2014): 2670–71. http://dx.doi.org/10.1109/tps.2014.2326459.

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32

Sun, Haomin, Yan Yang, Quanming Lu, San Lu, Minping Wan e Rongsheng Wang. "Physical Regimes of Two-dimensional MHD Turbulent Reconnection in Different Lundquist Numbers". Astrophysical Journal 926, n. 1 (1 febbraio 2022): 97. http://dx.doi.org/10.3847/1538-4357/ac4158.

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Abstract Using two-dimensional MHD simulations in different Lundquist numbers S, we investigate physical regimes of turbulent reconnection and the role of turbulence in enhancing the reconnection rate. Turbulence is externally injected into the system with varying strength. Externally driven turbulence contributes to the conversion of magnetic energy to kinetic energy flowing out of the reconnection site and thus enhances the reconnection rate. The plasmoids formed in high Lundquist numbers contribute to the fast reconnection rate, as well. Moreover, an analysis of the power of turbulence implies its possible association with the generation of plasmoids. Additionally, the presence of turbulence has great impact on the magnetic energy conversion and may be impactful also for the Kelvin–Helmholtz instability in the magnetic reconnection process.

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33

Mészárosová, Hana, Ján Rybák, Marian Karlický e Karel Jiřička. "Separation of solar radio bursts in a complex spectrum". Proceedings of the International Astronomical Union 6, S274 (settembre 2010): 150–52. http://dx.doi.org/10.1017/s1743921311006788.

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AbstractRadio spectra, observed during solar flares, are usually very complex (many bursts and fine structures). We have developed a new method to separate them into individual bursts and analyze them separately. The method is used in the analysis of the 0.8–2.0 GHz radio spectrum of the April 11, 2001 event, which was rich in drifting pulsating structures (DPSs). Using this method we showed that the complex radio spectrum consists of at least four DPSs separated with respect to their different frequency drifts (−115, −36, −23, and −11 MHz s−1). These DPSs indicate a presence of at least four plasmoids expected to be formed in a flaring current sheet. These plasmoids produce the radio emission on close frequencies giving thus a mixture of superimposed DPSs observed in the radio spectrum.

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34

Zhang, Hao, Lorenzo Sironi e Dimitrios Giannios. "Fast Particle Acceleration in Three-dimensional Relativistic Reconnection". Astrophysical Journal 922, n. 2 (1 dicembre 2021): 261. http://dx.doi.org/10.3847/1538-4357/ac2e08.

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Abstract Magnetic reconnection is invoked as one of the primary mechanisms to produce energetic particles. We employ large-scale 3D particle-in-cell simulations of reconnection in magnetically dominated (σ = 10) pair plasmas to study the energization physics of high-energy particles. We identify an acceleration mechanism that only operates in 3D. For weak guide fields, 3D plasmoids/flux ropes extend along the z-direction of the electric current for a length comparable to their cross-sectional radius. Unlike in 2D simulations, where particles are buried in plasmoids, in 3D we find that a fraction of particles with γ ≳ 3σ can escape from plasmoids by moving along z, and so they can experience the large-scale fields in the upstream region. These “free” particles preferentially move in z along Speiser-like orbits sampling both sides of the layer and are accelerated linearly in time—their Lorentz factor scales as γ ∝ t, in contrast to γ ∝ t in 2D. The energy gain rate approaches ∼eE rec c, where E rec ≃ 0.1B 0 is the reconnection electric field and B 0 the upstream magnetic field. The spectrum of free particles is hard, dN free / d γ ∝ γ − 1.5 , contains ∼20% of the dissipated magnetic energy independently of domain size, and extends up to a cutoff energy scaling linearly with box size. Our results demonstrate that relativistic reconnection in GRB and AGN jets may be a promising mechanism for generating ultra-high-energy cosmic rays.

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35

Moldwin, Mark B., e W. Jeffrey Hughes. "Observations of earthward and tailward propagating flux rope plasmoids: Expanding the plasmoid model of geomagnetic substorms". Journal of Geophysical Research 99, A1 (1994): 183. http://dx.doi.org/10.1029/93ja02102.

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36

Sindhu, M. S., G. Renuka e C. Venugopal. "Particle diffusion and adiabatic expansion of plasmoids". Journal of Earth System Science 104, n. 1 (marzo 1995): 37–47. http://dx.doi.org/10.1007/bf02842274.

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37

Hughes, W. J., e D. G. Sibeck. "On the 3-dimensional structure of plasmoids". Geophysical Research Letters 14, n. 6 (giugno 1987): 636–39. http://dx.doi.org/10.1029/gl014i006p00636.

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38

Nemati, M. J., Z. X. Wang e Lai Wei. "FORMATION OF PLASMOIDS IN MULTIPLE CURRENT SYSTEMS". Astrophysical Journal 821, n. 2 (22 aprile 2016): 128. http://dx.doi.org/10.3847/0004-637x/821/2/128.

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39

Scholer, M., e F. Jamitzky. "Particle orbits during the development of plasmoids". Journal of Geophysical Research 92, A11 (1987): 12181. http://dx.doi.org/10.1029/ja092ia11p12181.

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40

Furov, L. V. "A Generator of Long-Lived Isolated Plasmoids". Instruments and Experimental Techniques 47, n. 5 (settembre 2004): 701–2. http://dx.doi.org/10.1023/b:inet.0000043885.72569.33.

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41

Mukai, T. "Plasma distribution functions in plasmoids: GEOTAIL observations". Advances in Space Research 26, n. 3 (gennaio 2000): 415–24. http://dx.doi.org/10.1016/s0273-1177(99)01084-4.

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42

Dubowsky, Scott E., David M. Friday, Kevin C. Peters, Zhangji Zhao, Richard H. Perry e Benjamin J. McCall. "Mass spectrometry of atmospheric-pressure ball plasmoids". International Journal of Mass Spectrometry 376 (gennaio 2015): 39–45. http://dx.doi.org/10.1016/j.ijms.2014.11.011.

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43

Dvornikov, Maxim. "Quantum exchange interaction of spherically symmetric plasmoids". Journal of Atmospheric and Solar-Terrestrial Physics 89 (novembre 2012): 62–66. http://dx.doi.org/10.1016/j.jastp.2012.08.005.

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44

Chutov, Yu I., A. Yu Kravchenko e V. V. Pikozh. "Expansion of plasmoids in a neutral gas". Journal of Mathematical Sciences 71, n. 4 (settembre 1994): 2558–62. http://dx.doi.org/10.1007/bf02111955.

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45

YANG, Hong-Ang, e Shu-Ping JIN. "Numerical Study on the Earthward Propagating Plasmoids". Chinese Journal of Geophysics 45, n. 5 (settembre 2002): 639–53. http://dx.doi.org/10.1002/cjg2.278.

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46

Peter, H., Y. M. Huang, L. P. Chitta e P. R. Young. "Plasmoid-mediated reconnection in solar UV bursts". Astronomy & Astrophysics 628 (25 luglio 2019): A8. http://dx.doi.org/10.1051/0004-6361/201935820.

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Abstract (sommario):

Context. Ultraviolet bursts are transients in the solar atmosphere with an increased impulsive emission in the extreme UV lasting for one to several tens of minutes. They often show spectral profiles indicative of a bi-directional outflow in response to magnetic reconnection. Aims. To understand UV bursts, we study how motions of magnetic elements at the surface can drive the self-consistent formation of a current sheet resulting in plasmoid-mediated reconnection. In particular, we want to study the role of the height of the reconnection in the atmosphere. Methods. We conducted numerical experiments solving the 2D magnetohydrodynamic equations from the solar surface to the upper atmosphere. Motivated by observations, we drove a small magnetic patch embedded in a larger system of magnetic field of opposite polarity. This type of configuration creates an X-type neutral point in the initial potential field. The models are characterized by the (average) plasma-β at the height of this X point. Results. The driving at the surface stretches the X-point into a thin current sheet, where plasmoids appear, accelerating the reconnection, and a bi-directional jet forms. This is consistent with what is expected for UV bursts or explosive events, and we provide a self-consistent model of the formation of the reconnection region in such events. The gravitational stratification gives a natural explanation for why explosive events are restricted to a temperature range around a few 0.1 MK, and the presence of plasmoids in the reconnection process provides an understanding of the observed variability during the transient events on a timescale of minutes. Conclusions. Our numerical experiments provide a comprehensive understanding of UV bursts and explosive events, in particular of how the atmospheric response changes if the reconnection happens at different plasma-β, that is, at different heights in the atmosphere. This analysis also gives new insight into how UV bursts might be related to the photospheric Ellerman bombs.

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47

Dihingia, Indu K., Bhargav Vaidya e Christian Fendt. "Jets, disc-winds, and oscillations in general relativistic, magnetically driven flows around black hole". Monthly Notices of the Royal Astronomical Society 505, n. 3 (27 maggio 2021): 3596–615. http://dx.doi.org/10.1093/mnras/stab1512.

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ABSTRACT Relativistic jets and disc-winds are typically observed in black hole X-ray binaries (BH-XRBs) and active galactic nuclei. However, many physical details of jet launching and the driving of disc winds from the underlying accretion disc are still not fully understood. In this study, we further investigate the role of the magnetic field strength and structure in launching jets and disc winds. In particular, we explore the connection between jet, wind, and the accretion disc around the central black hole. We perform axisymmetric general relativistic magneto-hydrodynamical simulations of the accretion-ejection system using adaptive mesh refinement. Essentially, our simulations are initiated with a thin accretion disc in equilibrium. An extensive parametric study by choosing different combinations of magnetic field strength and initial magnetic field inclination is also performed. Our study finds relativistic jets driven by the Blandford & Znajek mechanism and the disc-wind driven by the Blandford & Payne (BP) mechanism. We also find that plasmoids are formed due to the reconnection events, and these plasmoids advect with disc-winds. As a result, the tension force due to the poloidal magnetic field is enhanced in the inner part of the accretion disc, resulting in disc truncation and oscillation. These oscillations result in flaring activities in the jet mass flow rates. We find simulation runs with a lower value of the plasma-β, and lower inclination angle parameters are more prone to the formation of plasmoids and subsequent inner disc oscillations. Our models provide a possible template to understand spectral state transition phenomena in BH-XRBs.

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48

Maiden, Martha E., e W. A. Christiansen. "Hercules A: a precessing cannon?" Canadian Journal of Physics 64, n. 4 (1 aprile 1986): 490–94. http://dx.doi.org/10.1139/p86-092.

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Hercules A is an unusual radio source in that its structure is dominated (most specifically on the western side of the source) by an undulating chain of discrete "rings" of radio emission, whose individual radii increase progressively with distance from the nuclear core while their apparent separation decreases. In the theoretical model presented here, these interesting radio features are presumed to be due to emission from a discrete set of ram-pressure confined plasmoids that have been periodically ejected by a precessing nuclear engine. The predicted deceleration and expansion of these ram-pressure confined plasmoids provides an excellent fit to the observed spacing and radii of the radio rings observed on the western side of Hercules A. Furthermore, a satisfactory fit to the morphology of the undulating eastern jet can also be achieved using this discrete ejection model, providing the eastward ejections alternate with the westward ejections, thus implying a form of flip-flop behavior for this particular source.

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49

Hakobyan, Hayk, Maria Petropoulou, Anatoly Spitkovsky e Lorenzo Sironi. "Secondary Energization in Compressing Plasmoids during Magnetic Reconnection". Astrophysical Journal 912, n. 1 (1 maggio 2021): 48. http://dx.doi.org/10.3847/1538-4357/abedac.

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50

WENZEL, Uwe. "Ascent Velocity of Plasmoids Generated by Surface Discharges". Plasma and Fusion Research 4 (2009): 046. http://dx.doi.org/10.1585/pfr.4.046.

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