Reconnection Of Lines Research Articles

Distinctive features of measuring <I>T<SUB>e</SUB></I> and <I>n<SUB>e</SUB></I> spatial distributions in the Globus-M2 spherical tokamak using method of Thomson scattering of laser radiation

The results of measuring the electron temperature and density spatial distributions in plasma of the Globus-M2 tokamak using the Thomson scattering diagnostics are presented. The diagnostics provides measurements throughout the entire tokamak discharge, starting from time of gas breakdown. The Thomson scattering data were analyzed in order to determine the positions of the last closed flux surface, the plasma magnetic axis, and the radius of inversion during the saw-tooth oscillations. The results of measurements performed during the internal reconnection of magnetic field lines are presents, as well as the dynamics of spatial distributions of electron temperature, density and pressure during the plasma transition to the H-mode. The results of measuring the electron temperature distribution in the scrape-off layer using the Thomson scattering diagnostics are also presented for distances up to 4 cm outside the last closed flux surface.

Simulation of Interaction Between Proton‐Electron Plasma Beam and Arched Magnetic Field

ABSTRACTThe present study investigates the interaction between a proton‐electron plasma beam and an arched magnetic trap using the particle‐in‐cell (PIC) simulation method. The results show that when the magnetic field is sufficiently weak, the beam disrupts the arched magnetic field configuration, causing the breaking and reconnection of magnetic field lines. The relationships between the coil current threshold (the coil current at which the disruption of the magnetic induction just happens) and initial plasma velocity, and between the critical beam velocity (the plasma is just enough to reach the arched magnetic field) and coil current, are quantified. Additionally, the interaction between the beam and the arched magnetic field is observed to induce microwave excitation. These findings lay the foundation for theoretically simulating the dynamic behavior of space plasma in a unique magnetic field environment within a laboratory setting.

Sunward Oxygen Ion Fluxes and the Magnetic Field Topology at Mars From Hybrid Simulations

AbstractIt is commonly believed that because of the direct solar wind interaction with the Martian atmosphere/ionosphere, the planet could have lost a significant part of its atmosphere. Closed field lines of the crustal magnetic field can weaken a transport of the ionospheric ions to the tail. Reconnection of the interplanetary magnetic field lines draping around Mars and the crustal magnetic field can also lead to a presense of sunward fluxes of planetary ions that might affect the total ion loss. The LatHyS (LATMOS Hybrid Simulation) three‐dimensional multispecies hybrid model is used here to characterize sunward fluxes of O+ ions and the magnetic field topology at Mars. It is shown that although reconnection between the interplanetary magnetic field (IMF) and the crustal magnetic fields strongly modifies the field topology, then sunward ion fluxes are rather small and do not significantly change the total ion loss.

Approach and rotation of reconnecting topological defect lines in liquid crystal

Topological defects are a universal concept across many disciplines, such as crystallography, liquid-crystalline physics, low-temperature physics, cosmology, and even biology. In nematic liquid crystals, topological defects called disclinations have been widely studied. For their three-dimensional (3D) dynamics, however, only recently have theoretical approaches dealing with fully 3D configurations been reported. Further, recent experiments have observed 3D disclination line reconnections, a phenomenon characteristic of defect line dynamics, but detailed discussions were limited to the case of approximately parallel defects. In this paper, we focus on the case of two disclination lines that approach at finite angles and lie in separate planes, a more fundamentally 3D reconnection configuration. Observing and analyzing such reconnection events, we find the square-root law of the distance between disclinations and the decrease of the interdisclination angle over time. We compare the experimental results with theory and find qualitative agreement on the scaling of distance and angle with time, but quantitative disagreement on distance and angle relative mobilities. To probe this disagreement, we derive the equations of motion for systems with reduced twist constant and also carry out simulations for this case. These, together with the experimental results, suggest that deformations of disclinations may be responsible for the disagreement. Published by the American Physical Society 2024

Finding reconnection lines and flux rope axes via local coordinates in global ion-kinetic magnetospheric simulations

Abstract. Magnetic reconnection is a crucially important process for energy conversion in plasma physics, with the substorm cycle of Earth's magnetosphere and solar flares being prime examples. While 2D models have been widely applied to study reconnection, investigating reconnection in 3D is still, in many aspects, an open problem. Finding sites of magnetic reconnection in a 3D setting is not a trivial task, with several approaches, from topological skeletons to Lorentz transformations, having been proposed to tackle the issue. This work presents a complementary method for quasi-2D structures in 3D settings by noting that the magnetic field structures near reconnection lines exhibit 2D features that can be identified in a suitably chosen local coordinate system. We present applications of this method to a hybrid-Vlasov Vlasiator simulation of Earth's magnetosphere, showing the complex magnetic topologies created by reconnection for simulations dominated by quasi-2D reconnection. We also quantify the dimensionalities of magnetic field structures in the simulation to justify the use of such coordinate systems.

Statistical Survey of Thin Current Sheets in Earth's Magnetotail: MMS Observations

AbstractThin current sheets (TCS) formed in Earth's magnetotail and hosting magnetic field line reconnection are important element of magnetospheric dynamics. In this paper, a statistical survey of 163 TCS crossing events in Earth's magnetotail using observations by MMS during 2017–2020 is performed. We find that magnetotail TCSs typically have a very strong current density primarily carried by electrons, with a thickness of a few ion inertial lengths. Our statistical results reveal different characteristics between TCSs located on the duskside and dawnside. Specifically, we find that TCSs on the duskside have a smaller thickness, higher current density, and stronger Hall electric field than on the dawnside. Our results also show that there is a correlation between the TCS thickness and the Hall electric field magnitude, with a stronger Hall electric field present in thinner TCSs. Our statistics results confirm previously reported key TCS dawn‐dusk asymmetries, with the main advance of directly measurable plasma currents. TCS characteristics of the presented data set will be useful for initialization of realistic numerical simulations and theoretical investigations of TCS instabilities resulted in various dynamical models of the magnetotail.

Gradient profile for the reconnection of vortex lines with the boundary in type-II superconductors

Gradient profile for the reconnection of vortex lines with the boundary in type-II superconductors

Multi‐Scale Observation of Magnetotail Reconnection Onset: 2. Microscopic Dynamics

AbstractWe analyze the local dynamics of magnetotail reconnection onset using Magnetospheric Multiscale (MMS) data. In conjunction with MMS, the macroscopic dynamics of this event were captured by a number of other ground and space‐based observatories, as is reported in a companion paper. We find that the local dynamics of the onset were characterized by the rapid thinning of the cross‐tail current sheet below the ion inertial scale, accompanied by the growth of flapping waves and the subsequent onset of electron tearing. Multiple kinetic‐scale magnetic islands were detected coincident with the growth of an initially sub‐Alfvénic, demagnetized tailward ion exhaust. The onset and rapid enhancement of parallel electron inflow at the exhaust boundary was a remote signature of the intensification of reconnection Earthward of the spacecraft. Two secondary reconnection sites are found embedded within the exhaust from a primary X‐line. The primary X‐line was designated as such on the basis that (a) while multiple jet reversals were observed in the current sheet, only one reversal of the electron inflow was observed at the high‐latitude exhaust boundary, (b) the reconnection electric field was roughly five times larger at the primary X‐line than the secondary X‐lines, and (c) energetic electron fluxes increased and transitioned from anti‐field‐aligned to isotropic during the primary X‐line crossing, indicating a change in magnetic topology. The results are consistent with the idea that a primary X‐line mediates the reconnection of lobe magnetic field lines and accelerates electrons more efficiently than its secondary X‐line counterparts.

Methods and techniques for increasing the safety and efficacy of pulmonary vein isolation in patients with atrial fibrillation.

The most common type of sustained arrhythmia is atrial fibrillation (AF). Pulmonary vein isolation (PVI) is the cornerstone of catheter ablation for atrial fibrillation, which has emerged as the primary therapeutic strategy for atrial fibrillation patients. Unfortunately, about one-third of patients experience recurrent atrial arrhythmias after the procedure.

RADIO EMISSION SPECTRUM OF COMPOSITE SUPERNOVA REMNANT G74.9+1.2

Measurements of the flux densities of the supernova remnant (SNR) G74.9+1.2 (CTB 87) at frequencies of 4840 and 8450 MHz were carried out with the RT-32 radio telescope of the Svetloye observatory of the IAA RAS in 2018–2019. The data obtained contain signs of the presence of a source of a variable component in the radio emission on a time scale of a month or more. The flux densities of G74.9+1.2 over the time interval 1959.7–2010 are determined from published data, which makes it possible to compare the intensities of G74.9+1.2 and standard sources. All data are presented in a single system based on the exact scale of “artificial moon” (AM) fluxes. A refined spectrum of SOS G74.9+1.2 was obtained. The totality of available data is approximated by two power-law sections with different spectral indices: \({{\alpha }_{1}} = 0.31\) at frequencies \(f {{f}_{b}}\) and \({{\alpha }_{2}} = 0.71\) at \(f {{f}_{b}}\). The projections of two power law sections intersect at a frequency \({{f}_{b}} \approx 3409\) MHz. The break in the radio spectrum of the source, taking into account its age (more than 4000 years), could be formed as a result of synchrotron losses. The increase in the steepness of the spectrum close to 0.5 above the frequency \({{f}_{b}}\) is an argument in favor of such an assumption. The totality of data obtained during measurements on the RT-32 and on the basis of published works allows us to state that the variable component in the G74.9+1.2 radio emission on all time scales is much less pronounced compared to younger PWNs. As a possible mechanism for the observed variability, a reconnection of the magnetic field lines in the pulsar magnetosphere is proposed.

Automated precision localization of peripherally inserted central catheter tip through model-agnostic multi-stage networks

Background:Peripherally inserted central catheters (PICCs) have been widely used as one of the representative central venous lines (CVCs) due to their long-term intravascular access with low infectivity. However, PICCs have a fatal drawback of a high frequency of tip mispositions, increasing the risk of puncture, embolism, and complications such as cardiac arrhythmias. To automatically and precisely detect it, various attempts have been made by using the latest deep learning (DL) technologies. However, even with these approaches, it is still practically difficult to determine the tip location because the multiple fragments phenomenon (MFP) occurs in the process of predicting and extracting the PICC line required before predicting the tip. Objective:This study aimed to develop a system generally applied to existing models and to restore the PICC line more exactly by removing the MFs of the model output, thereby precisely localizing the actual tip position for detecting its misposition. Methods:To achieve this, we proposed a multi-stage DL-based framework post-processing the PICC line extraction result of the existing technology. Our method consists of the following three stages: 1. Existing PICC line segmentation network for a baseline, 2. Patch-based PICC line refinement network, 3. PICC line reconnection network. The proposed second and third-stage models address MFs caused by the sparseness of the PICC line and the line disconnection due to confusion with anatomical structures respectively, thereby enhancing tip detection. Results:To verify the objective performance of the proposed MFCN, internal validation and external validation were conducted. For internal validation, learning (130 samples) and verification (150 samples) were performed with 280 data, including PICC among Chest X-ray (CXR) images taken at our institution. External validation was conducted using a public dataset called the Royal Australian and New Zealand College of Radiologists (RANZCR), and training (130 samples) and validation (150 samples) were performed with 280 data of CXR images, including PICC, which has the same number as that for internal validation. The performance was compared by root mean squared error (RMSE) and the ratio of single fragment images (RatioSFI) (i.e., the rate at which model predicts PICC as multiple sub-lines) according to whether or not MFCN is applied to seven conventional models (i.e., FCDN, UNET, AUNET, TUNET, FCDN-HT, UNET-ELL, and UNET-RPN). In internal validation, when MFCN was applied to the existing single model, MFP was improved by an average of 45 %. The RMSE improved over 63% from an average of 27.54 mm (17.16 to 35.80 mm) to 9.77 mm (9.11 to 10.98 mm). In external validation, when MFCN was applied, the MFP incidence rate decreased by an average of 32% and the RMSE decreased by an average of 65%. Therefore, by applying the proposed MFCN, we observed the consistent detection performance improvement of PICC tip location compared to the existing model. Conclusion:In this study, we applied the proposed technique to the existing technique and demonstrated that it provides high tip detection performance, proving its high versatility and superiority. Therefore, we believe, in countries and regions where radiologists are scarce, that the proposed DL approach will be able to effectively detect PICC misposition on behalf of radiologists.

Rotational Flows in Solar Coronal Flux Rope Cavities

We present a 2.5D magnetohydrodynamic simulation of a systematically rotating prominence inside its coronal cavity using the open-source MPI-AMRVAC code. Our simulation starts from a nonadiabatic, gravitationally stratified corona, permeated with a sheared arcade magnetic structure. The flux rope (FR) is formed through converging and shearing footpoints driving, simultaneously applying randomized heating at the bottom. The latter induces a left–right asymmetry of temperature and density distributions with respect to the polarity inversion line. This asymmetry drives flows along the loops before the FR formation, which gets converted to net rotational motions upon reconnection of the field lines. As the thermal instability within the FR develops, angular momentum conservation about its axis leads to a systematic rotation of both hot coronal and cold condensed plasma. The initial rotational velocity exceeds 60 km s−1. The synthesized images confirm the simultaneous rotations of the coronal plasma seen in 211 and 193 Å and condensations seen in 304 Å. Furthermore, the formation of the dark cavity is evident in 211 and 193 Å images. Our numerical experiment is inspired by observations of so-called giant solar prominence tornadoes and reveals that asymmetric FR formation can be crucial in triggering rotational motions. We reproduce observed spinning motions inside the coronal cavity, augmenting our understanding of the complex dynamics of rotating prominences.

Regimes of ion dynamics in current sheets: The machine learning approach.

Current sheets are spatially localized almost-one-dimensional (1D) structures with intense plasma currents. They play a key role in storing the magnetic field energy and they separate different plasma populations in planetary magnetospheres, the solar wind, and the solar corona. Current sheets are primary regions for the magnetic field line reconnection responsible for plasma heating and charged particle acceleration. One of the most interesting and widely observed types of 1D current sheets is the rotational discontinuity, which can be force-free or include plasma compression. Theoretical models of such 1D current sheets are based on the assumption of adiabatic motion of ions, i.e., ion adiabatic invariants are conserved. We focus on three current sheet configurations, widely observed in the Earth magnetopause and magnetotail and in the near-Earth solar wind. The magnetic field in such current sheets is supported by currents carried by transient ions, which exist only when there is a sufficient number of invariants. In this paper, we apply a machine learning approach, AI Poincaré, to determine parametrical domains where adiabatic invariants are conserved. For all three current sheet configurations, these domains are quite narrow and do not cover the entire parametrical range of observed current sheets. We discuss possible interpretation of obtained results indicating that 1D current sheets are dynamical rather than static plasma equilibria.

Reconnection-driven energy cascade in magnetohydrodynamic turbulence.

Magnetohydrodynamic turbulence regulates the transfer of energy from large to small scales in many astrophysical systems, including the solar atmosphere. We perform three-dimensional magnetohydrodynamic simulations with unprecedentedly large magnetic Reynolds number to reveal how rapid reconnection of magnetic field lines changes the classical paradigm of the turbulent energy cascade. By breaking elongated current sheets into chains of small magnetic flux ropes (or plasmoids), magnetic reconnection leads to a previously undiscovered range of energy cascade, where the rate of energy transfer is controlled by the growth rate of the plasmoids. As a consequence, the turbulent energy spectra steepen and attain a spectral index of -2.2 that is accompanied by changes in the anisotropy of turbulence eddies. The omnipresence of plasmoids and their consequences on, for example, solar coronal heating, can be further explored with current and future spacecraft and telescopes.

A Very Large Array Study of Newly Discovered Southern Latitude Nonthermal Filaments in the Galactic Center: Radio Continuum Total-intensity and Spectral Index Properties

The nonthermal filament (NTF) radio structures clustered within a few hundred parsecs of the Galactic center (GC) are apparently unique to this region of the Galaxy. Recent radio images of the GC using MeerKAT at 1 GHz have revealed a multitude of faint, previously unknown NTF bundles (NTFBs), some of which are comprised of as many as 10 or more individual filaments. In this work we present Very Large Array observations at the C- and X-bands (4–12 GHz) at arcsecond-scale resolutions of three of these newly discovered NTFBs, all located at southern Galactic latitudes. These observations allow us to compare their total-intensity properties with those of the larger NTF population. We find that these targets generally possess properties similar to what is observed in the larger NTF population. However, the larger NTF population generally has steeper spectral indices than what we observe for our chosen targets. The results presented here based on the total-intensity properties of these structures indicate that the NTFs are likely a result of synchrotron emission from relativistic electrons that have been generated either by a nearby compact source or by extended magnetic field structures in which the magnetic field line reconnection has accelerated the electrons. In either scenario, once the relativistic electrons are produced and injected locally into the field they diffuse along the magnetic field lines, producing the filaments.

The Location and Angle Distribution of Magnetic Reconnection in the Solar Corona

A major unresolved issue in solar physics is the nature of the reconnection events that may give rise to the extreme temperatures measured in the solar corona. In the nanoflare heating paradigm of coronal heating, localized reconnection converts magnetic energy into thermal energy, producing multithermal plasma in the corona. The properties of the corona produced by magnetic reconnection, however, depend on the details of the reconnection process. A significant challenge in understanding the details of reconnection in magnetohydrodynamic (MHD) models is that these models are frequently only able to tell us that reconnection has occurred, but there is significant difficulty in identifying precisely where and when it occurred. In order to properly understand the consequences of reconnection in MHD models, it is crucial to identify reconnecting field lines and where along the field lines reconnection occurs. In this work, we analyze a fully 3D MHD simulation of a realistic sunspot topology, driven by photospheric motions, and we present a model for identifying reconnecting field lines. We also present a proof-of-concept model for identifying the location of reconnection along the reconnecting field lines, and use that to measure the angle at which reconnection occurs in the simulation. We find evidence that magnetic reconnection occurs preferentially near field line footpoints, and discuss the implications of this for coronal heating models.

Ultra-High-Energy Particles at the Border of Kerr Black Holes Triggered by Magnetocentrifugal Winds

The source, origin, and acceleration mechanisms of ultra-high-energy cosmic rays (UHECR) (E>1020 eV, beyond the GZK limit) remain uncertain and unclear. The main explanations are associated with particular mechanisms, such as the Fermi mechanism, in which charged particles could be accelerated by clouds of magnetized gas moving within our Galaxy, or by the magnetic reconnection of field lines at, e.g., the core of high-energy astrophysical sources, where the topology of the magnetic field is rearranged and magnetic energy is converted into kinetic energy. However, the recent observation of extragalactic neutrinos may suggest that the source of UHECRs is likely an extragalactic supermassive black hole. In the present work, we propose that charged particles can be accelerated to ultrahigh energies in marginally bound orbits near extreme rotating black holes and could be triggered by collisions of magnetocentrifugal winds; the accretion disk surrounding the black hole would provide such winds. The ultra-high-energy process is governed by the frame-dragging effects of the black hole spacetime.

On the Magnetic Dip Ahead of the Dipolarization Fronts

AbstractDipolarization front (DF), a transient structure that is associated with the earthward plasma flow, is widely considered as a result of magnetic reconnection. It is often characterized with a sharp increase in the northward magnetic field Bz preceded by a minor decrease of it. However, the small magnetic dip ahead of the DF is not always present, the reason of which is not well known. By analyzing in site Magnetospheric MultiScale spacecraft measurements at the magnetotail, we present two events of DF with and without a dip ahead of it. It is found that the magnetic dip ahead of DF is accompanied by a guide field By. To investigate the physical mechanism that determines the appearance of the dip, we perform kinetic simulations of symmetric single X line magnetic reconnection under various guide fields. The simulation results show that the dip is generated due to the separation of the gyro‐motion between ions and electrons under the influence of the guide field. Ions are reflected at the DF and further deviated by the guide field away from the neutral sheet, while more electrons remain in the neutral sheet due to their small gyroradius. In the absence of a compensating ion current, a dawnward current thus is formed, carried by the electrons, and generates the dip. Our results bring in a new perspective on the formation of the dip in single X line reconnection.

Reconnection patterns after CLOSE-guided 50 W high-power-short-duration circumferential pulmonary vein isolation and substrate modification-PV reconnection might no longer be an issue.

Ablation of atrial fibrillation (AF) with high-power-short-duration (HPSD) radiofrequency (RF) technology is emerging as a new standard of care in many electrophysiology laboratories. While procedural short-term efficacy and efficiency is very promising, little is known about mid- to long-term effects of HPSD ablation for pulmonary vein isolation (PVI) and left atrial substrate modification. In a single-center registry, 412 AF procedures were performed in 400 individual patients using a standardized CLOSE protocol-guided fixed 50 W HPSD ablation, aiming for an ablation index (AI) of 400 on the posterior and 550 on the anterior wall. Additional substrate-tailored lines were performed when required. After a mean clinical follow-up of 337 ± 134 days, 15 patients suffered from AF recurrence beyond the blinding period. Twelve gave consent to the indicated reablation. Here, 11 of 12 patients had chronic isolation of all fourpulmonary veins (PV). In three of sixpatients, a reconnection of additional left atrial ablation lines was revealed. Ten out of 12 patients showed progressive fibrous atrial cardiomyopathy and required additional left atrial substrate modification or reisolation of left-atrial lines. During the follow-up no clinical case of atrioesophageal fistula was registered. No PV stenosis after initial HPSD PVI was documented. Patients requiring reablation of AF or other atrial tachycardia after a fixed 50 W HPSD circumferential PVI and substrate modification predominantly suffer from progressive fibrous atrial cardiomyopathy, while PV reconnection appears to be a rare cause of AF recurrence.

Magnetic reconnection and energy extraction from a spinning black hole with broken Lorentz symmetry

In the Penrose process and the Blandford-Znajek mechanism, the rotational energy of a black hole (BH) is extracted via particle fission and magnetic tension, respectively. Recently, inspired by a fundamental trait in plasma astrophysics known as magnetic reconnection (MR), a new energy extraction mechanism based on the fast reconnection of the magnetic field lines inside the ergosphere has been proposed by Comisso and Asenjo. In this paper, we investigate energy extraction caused by MR in the ergosphere of a rapidly spinning BH with broken Lorentz symmetry by a background bumblebee vector field. The desired rotating BH solution differentiates from the standard Kerr BH via the Lorentz symmetry breaking (LSB) parameter $l$, which comes from nonminimal coupling between the bumblebee field with nonzero vacuum expectation value and gravity. We find that incorporating $l<0$ in the background is in the interest of the energy extraction via MR for the fast-spinning BH surrounded by the plasma with weak magnetization, below what is expected from the scenario by Comisso and Asenjo. Our analysis robustly indicates that the power of energy extraction and efficiency of the plasma energization process through fast MR is more efficient than the Comisso-Asenjo solution, provided that the LSB parameter is negative, $l<0$. Compared to the Blandford-Znajek mechanism arising from the underlying background, we also show that MR is a more efficient energy extraction mechanism if $l<0$.