Reconnection Rate Research Articles

First-Principles Theory of the Relativistic Magnetic Reconnection Rate in Astrophysical Pair Plasmas.

We develop a first-principles model for the relativistic magnetic reconnection rate in strongly magnetized pair plasmas. By considering the energy budget and required current density near the x-line, we analytically show that in the magnetically dominated relativistic regime, the x-line thermal pressure is significantly lower than the upstream magnetic pressure due to the extreme energy needed to sustain the current density, consistent with kinetic simulations. This causes the upstream magnetic field lines to collapse in, producing the open outflow geometry which enables fast reconnection. The result is important for understanding a wide range of extreme astrophysical environments, where fast reconnection has been evoked to explain observations such as transient flares and nonthermal particle signatures.

The adjunctive effect for left pulmonary vein isolation of vein of Marshall ethanol infusion in persistent atrial fibrillation.

This study sought to assess the effect of ethanol infusion into the vein of Marshall (EIVOM) on the acute success of left pulmonary vein (LPV) isolation in persistent atrial fibrillation (PeAF). A total of 313 patients with drug-resistant PeAF were enrolled (135 in Group 1 and 178 in Group 2). In Group 1, EIVOM was firstly performed, followed by radiofrequency ablation (RFA) including bilateral pulmonary vein isolation (PVI) and linear ablation at roofline, cavotricuspid isthmus, and mitral isthmus (MI). In Group 2, PVI and linear ablations were completed with RFA. First-pass isolation of the LPV was achieved in 119 (88.1%) and 132 (74.2%) patients in Groups 1 and 2, respectively (P = 0.002). The rate of acute pulmonary vein reconnection (PVR) was significantly lower in Group 1 (9.6% vs. 22.5%, P = 0.003). About half of acute PVR occurred in the carina with or without EIVOM. EIVOM is effective in achieving a higher first-pass isolation and a lower acute PVR of LPV in PeAF.

Juno Magnetometer Observations at Ganymede: Comparisons With a Global Hybrid Simulation and Indications of Magnetopause Reconnection

AbstractJuno's flyby of Ganymede on 7 June 2021, provides a unique opportunity to explore the moon's magnetosphere. By means of Magnetometer (MAG) observations and a hybrid numerical simulation, we provide a global description of this environment and analyze the upstream magnetopause in detail. In particular, LATMOS Hybrid Simulation results suggest Juno observed open (one foot‐point connected to Ganymede, the other to Jupiter) and closed magnetic field lines along its trajectory. Additionally, we determine that the upstream magnetopause location and orientation seen by Juno MAG are consistent with previous Galileo observations. We observe a non‐zero normal component of the magnetic field across the magnetopause, along with flux rope structures embedded within the boundary's current sheet. Both signatures are strong indicators that magnetic reconnection was occurring along Ganymede's magnetopause. Based on this crossing, we calculate a shear angle of ∼78° across the magnetopause, with a dimensionless reconnection rate of ∼0.12.

Secondary island induced during magnetic reconnection by an external sub-Alfvénic shear flow

Secondary tearing instability induced associated with sub-Alfvénic shear flow during magnetic reconnection processes is investigated using a compressible resistive MHD model. Compared to the without shear flow case, it is found that a secondary island can be built up during the reconnection process with an external sub-Alfvénic shear flow. For further investigation, we also found that the built-up island is not developed so larger due to the pairs of discontinuities formed in the inflow region of the reconnection. For the fixed initial asymptotic shear flow velocity v0, there existing a critical value λvc fastest to excite the secondary island. The critical value λvc may vary with different v0. Although, there is a significant gap for reconnection rates between the simulation results and observations, it can be deduced that the discontinuities can be formed in the situations with sheared flows associated with the magnetic reconnection. The results can be applied to interpret the multiple-X lines reconnections and discontinuities observations at the Earth's dayside magnetopause and magnetotail.

Evidence of oblique electron acoustic solitary waves triggered by magnetic reconnection in Earth’s magnetosphere

Motivated by the recent Magnetospheric Multiscale (MMS) observations of oblique electron acoustic waves, we addressed the generation mechanism of the observed waves by utilizing the reductive perturbation technique. A nonlinear Zakharov-Kuznetsov (ZK) equation is derived for a collisionless, magnetised plasma composed of cool inertial background electrons, cool inertial electron beam, hot inertialess suprathermal electrons; represented by a κ-distribution, and stationary ions. Moreover, the instability growth rate is derived by using the small-k perturbation expansion method. Our findings revealed that the structure of the electrostatic wave profile is significantly influenced by the external magnetic field, the unperturbed hot, cool, and electron beam densities, the obliquity angle, and the rate of superthermality. Such parameters also have an effect on the instability growth rate. This study clarifies the characteristics of the oblique electron solitary waves that may be responsible for changing the electron and ion distribution functions, which alter the magnetic reconnection process. Moreover, the increase of the growth rate with the plasma parameters could be a source of anomalous resistivity that enhances the rate of magnetic reconnection.

Magnetic Reconnection Rates in a Confined X Class Flare

Magnetic Reconnection Rates in a Confined X Class Flare

Implications of High-density, High-temperature Ridges Observed in Some Two-ribbon Flares

Several two-ribbon solar flares observed on the disk, notably including the Bastille flare of 2000 July 14, show an extended ridge of plasma running along the loop tops of the post-reconnection arcade. In that and two more recent examples, the ridge is visible in emission by Fe xxiv at roughly 17 MK, with a high, steadily increasing emission measure suggesting an expanding column of very dense plasma. We find that ridges are consistent with overhead views of long, vertical plasma sheets, such as seen above certain limb flares. Those vertical features show enhanced temperature and density over their entire lengths, making explanations in terms of termination shocks and evaporation collision seem less plausible. We use observations of several ridge events to argue in favor of compression and heating by slow magnetosonic shocks in the reconnection outflow. In this scenario, the ridge is built up as retracting flux piles hot, compressed plasma atop the post-flare arcade. Thanks to the overhead perspective offered by the ridge observations, we are able to measure the reconnection rate and show it to be consistent with the rate of increase in column emission measure across the ridge. This consistency supports the hypothesis that slow shocks and retraction compress the plasma seen in ridges, vertical plasma sheets, and possibly the high-temperature fans through which post-reconnection downflows are observed. Such a unified picture of these diverse features enhances our understanding of the role played by magnetic reconnection in solar flares.

TOPOLOGICAL STUDY OF TORSIONAL SPINE MAGNETIC RECONNECTION AT NULL POINT

The spine is an isolated field line which approaches the null (or recedes from it), so called torsional spine reconnection occurs when field lines in the vicinity of the fan rotate, with current becoming concentrated along the spine so that nearby field lines undergo rotational slippage. In of these region, the spine and fan are perpendicular and there is no flux transfer across spine or fan. The geometry of the current layers within which torsional spine reconnection occur is strongly dependent on the symmetry of the magnetic field. Torsional spine reconnection occurs in a narrow tube around the spine, with elliptical crosssection when the fan eigenvalues are different. The eccentricity of the ellipse increases as the degree of asymmetry increases, with the short axis of the ellipse being along the strong field direction. The spatiotemporal peak current, and the peak reconnection rate attained, are found not to depend strongly on the degree of asymmetry.

Findings from repeat ablation using high-density mapping after pulmonary vein isolation with pulsed field ablation.

Pulsed-field ablation (PFA) can offer a novel perspective for atrial fibrillation (AF) ablation. We aimed to characterize the incidence of pulmonary vein (PV) reconnection, types of recurrent atrial tachyarrhythmia (ATa) and lesion quality after PFA-guided PV isolation (PVI). Patients undergoing second ablation for recurrent ATa following the initial PVI using the pentaspline PFA catheter were investigated. The rate of PV reconnection, the features of recurrent ATa, and the amount of isolated posterior wall (PW) surface area (ISAPW%) (ratio of the isolated- to total surface area on PW) were analyzed. Among 360 patients treated with PFA, 25 patients (paroxysmal AF, n = 19) with 99 PVs underwent a second procedure 6.1 ± 4.0 months after the initial procedure. The rate of PV reconnection was 9.1% (9 PVs). Patients presented with atrial tachycardia (AT) (n = 16), AF (n = 8) and typical atrial flutter (n = 1). The mechanism of all but one AT was macro-reentry. The critical isthmus was found to be linked to the initial lesion set at the left atrial (LA) PW in eight patients and linked to pre-existing substrate at the LA anterior wall in four patients. One AT had a focal origin at the septum. In three patients, AT were unmappable. Mean ISAPW% was 72.7 ± 19.0%. We revealed a remarkable low reconnection rate with a large antral lesion at the PW after pentaspline PFA catheter-guided PVI. However, macro-reentrant AT with a critical isthmus at the LAPW linked to the PVI lesion set was commonly observed.

Power-transfer and fixed-point analysis of sawtooth simulations of a current-carrying stellarator

Power-transfer and fixed-point analysis of previous NIMROD simulations (Roberds et al., Phys. Plasmas, vol. 23, issue 9, 2016, 092513) improved the understanding of the effect of 3D (non-axisymmetric equilibrium) magnetic fields on sawtooth oscillations in the Compact Toroidal Hybrid (CTH) experiment. Computing the locations of order-1 fixed points, their Greene's residues, and local values for the rotational transform results in a description of CTH sawteeth consistent with Kadomtsev's model. A power-transfer analysis quantifies the distribution of energy among toroidal Fourier modes and their nonlinear interactions. The Lorentz power transfer drives sawtooth growth, and it is unambiguously interpreted as the flow of energy from toroidal mode $n'$ to mode $n$ , catalysed by $\boldsymbol {B}_{n-n'}$ . It has been reported previously that the CTH sawtooth frequency increases with the 3D field strength. This is attributed to an increased growth rate of the internal kink that drives sawtooth oscillations. Here, 3D fields remove energy from the kink, eliminating the possibility that these fields are an additional energy source that drives growth. Instead, 3D fields catalyse energy transfer from large-to-small scales, where magnetic reconnection is stronger. It is proposed that this energy transfer increases the reconnection rate at small scales, which is consistent with the increased growth rate observed at higher 3D field strengths.

Abstract 14153: The Effect of Gender on Atrial Fibrillation Ablation Outcomes Using a Propensity Score Matched Analysis

Introduction: Previous studies have shown that woman with atrial fibrillation (AF) have increased non-pulmonary vein (PV) triggers which requires additional substrate modification during AF ablation. However, there remains an incomplete understanding of the impact of gender on AF ablation strategies and outcomes. Methods: At a single tertiary care center between January 2013 and July 2021, we analyzed 1576 AF ablations in 1412 patients, of whom 33% were female. Patients were followed for at least 6 months (mean 34 months) to detect AF recurrence, complications, and emergency room visits/hospitalizations. The effects of gender on AF clinical characteristics, AF recurrence, procedural approach and complications were assessed by multivariate logistic regression analysis using propensity score matching. Results: Of 1412 patients, mean age was 64 and mean BMI was 31 kg/m2. 77% underwent de novo ablations, and 27% patients had persistent AF at the time of ablation. The overall rate of AF recurrence was 37%. There was no difference in AF recurrence when stratified by gender (HR 1.15; CI: 0.92-1.43, p >0.05) and age (Fig. 1A & 1B). After propensity score matching gender 1:1 (criteria: age, type of AF, HTN, DM, and BMI, n = 888 patients), there was no difference in AF recurrence (Fig. 1C) or procedure related complications. Additional substrate modification was associated with persistent AF (OR 2.99; CI: 1.9-4.69, p <0.05) or age greater than 70 years (OR 1.03; CI: 1.02-1.05, p <0.05) with no difference based on gender. During ablation, first pass PV isolation was more likely achieved in males (OR 0.7; CI: 0.53-0.93, p <0.05) and patients with BMI < 30 kg/m2. There was no significant difference in the rate of PV reconnection during redo ablations between genders (OR 1.05; CI: 0.71-1.55, p >0.05). Conclusions: Despite a lower rate of first-pass PV isolation in female patients, there is no difference in overall safety or efficacy outcomes between genders following AF ablation.

Abstract 11177: Pulmonary Vein Reconnections Predict Good Clinical Outcomes After a Second Catheter Ablation of Persistent Atrial Fibrillation: Insight From the EARNEST-PVI Trial

Introduction: The effect of an extensive ablation strategy in addition to pulmonary vein (PV) isolation is still controversial in persistent atrial fibrillation (AF) ablation. Electrical PV reconnection is an important confounder affecting the trial results. Objectives: To evaluate the PV reconnection rate and association between the reconnection and AF recurrence after a re-do AF ablation in the EARNEST-PVI trial (NCT03514693). Methods: The analysis was performed using the extended data of the EARNEST-PVI trial (N=512), a randomized controlled trial to evaluate ablation strategies for persistent AF, which was conducted in the Osaka region of Japan. During a median follow-up of 47 months, a total of 126 (25%) patients underwent a re-do AF ablation. Among them, 120 (median age, 68 years; 36% female; 31% long-standing persistent AF, 95% contact force-sensing catheter use) whose follow-up data were available after the 2 nd AF ablation were enrolled in this study. Results: PV reconnections were observed in 75 (63%) patients. Although there was no difference in age, gender, long-standing persistent AF, and CA strategy during the index procedure, AF recurrence within 1 year was more frequent in patients with PV reconnections (81.3% vs. 64.4%, p = 0.039). During a median follow-up of 31 months after the re-do AF ablation, patients with PV reconnections had a lower clinical recurrence rate than those without (38.7 vs. 44.4%, log-rank p = 0.047). However, additional linear ablation did not affect the recurrence rate. Even after adjustment for age, gender, long-standing persistent AF, and presence of non-PV triggers, Cox regression analysis revealed that a number of reconnected PVs of ≥2 was independently associated with a lower recurrence of AF after the 2 nd AF ablation (hazard ratio, 0.36; 95% confidence interval, 0.19-0.67; p = 0.001). Conclusions: Among patients who underwent a redo-AF ablation in the EARNEST-PVI trial, about two-thirds exhibited PV reconnections. Patients with ≥2 PV reconnections had better clinical outcomes than those with ≤1 PV reconnections. A durable PV isolation is an important pre-requisite before exploring any additional ablation strategies for persistent AF.

Abstract 15077: Reconnection of Pulmonary Veins and Left Atrial Posterior Wall Following Catheter Ablation for Atrial Fibrillation in Real-World Patients: Registry Data From a High-Volume Center

Introduction: Durable isolation of the pulmonary veins (PV) and the left atrial posterior wall (LAPW) are considered as key determinants of long-term success after catheter ablation in AF patients. Objective: We aimed to evaluate the PV and LAPW reconnection rate in real-world patients undergoing redo-ablation at our center. Methods: Consecutive AF patients that underwent their first AF ablation at our center from 2015-19 were included in this analysis. At the index procedure, all received electrical isolation of PVs and the LAPW area between the PVs, using radiofrequency (RF) ablation. Procedure was conducted with 3.5-mm irrigated-tip catheter guided by circular mapping catheter, intra-cardiac echocardiography and a 3-D mapping system. RF energy was delivered with a maximum temperature setting of 42 0 C, contact force of 10g and a power of up to 45W. Posterior wall isolation was performed using multiple ablation points covering the whole posterior wall. An esophageal probe was utilized in all patients to monitor esophageal temperature during ablation in the LAPW in close proximity to the esophagus. Complete abolition of all PV potentials rather than decrease in the amplitudes was the end point and confirmed by entrance and/or exit block. All patients were followed up prospectively for 2 years with quarterly evaluation during the first year and bi-annually afterwards and the data was collected in our IRB-approved AF registry. Recovery of conduction in the PVs and LAPW were assessed at the redo procedure using pacing or incremental isoproterenol infusion of 20- 30μg/min for 15-20min. Results: During the study period, 6,817 AF ablation procedures were performed at our institution of which 3,113 AF patients undergoing their first catheter ablation were included in the analysis and prospectively followed up for 2 years. Baseline characteristics of the study population is given in Table 1. At 23.1±12.8 months of follow-up, 614 (19.7%) patients had received redo-ablation, of which 139 (22.6%) had one or more PV or LAPW reconnected. Conclusion: In this series, with experienced operators performing the procedures, the rate of recovery of conduction in the PVs and LAPW was low compared to the reported high incidence rate in the literature.

Scaling of reconnection parameters in magnetic island coalescence: Role of in-plane shear flow

A 2D incompressible viscoresistive-MHD model [Mahapatra et al., Phys. Plasmas 28, 072103 (2021)] is used to study the scaling of reconnection parameters in the magnetic island coalescence problem under two interesting scenarios. First, the effect of changing island half-width at a fixed system size is investigated. As the island half-width increases, the total magnetic flux content of the islands increases, resulting in an increase in upstream magnetic field, upstream velocity field, and unnormalized reconnection rate. However, the downstream magnetic field, current sheet length and normalized reconnection rate (normalized to the upstream magnetic field and upstream Alfvénic velocity) remain independent of it. Interestingly, the reconnection rate is found to be different from the upstream to downstream velocity ratio as well as from the aspect ratio of the current sheet, as opposed to the findings of the Sweet–Parker model. Second, the in-plane shear flow effects are studied, keeping the island width and system size fixed. Here, thickness and length of the current sheet, the upstream magnetic and velocity field components, reconnection rate and time, current sheet inclination angle with shear flow length scale, and amplitude are calculated. Interestingly, the inclination angle of the current sheet and the diffusion region are found to be different, and the differences are more in stronger shear flows. These results are significantly different from the Harris sheet setup with shear flow.

Evolution, Structure, and Topology of Self-generated Turbulent Reconnection Layers

We present a 3D MHD simulation of two merging flux ropes exhibiting self-generated and self-sustaining turbulent reconnection (SGTR) that is fully 3D and fast. The exploration of SGTR is crucial for understanding the relationship between MHD turbulence and magnetic reconnection in astrophysical contexts including the solar corona. We investigate the pathway toward SGTR and apply novel tools to analyze the structure and topology of the reconnection layer. The simulation proceeds from 2.5D Sweet–Parker reconnection to 2.5D nonlinear tearing, followed by a dynamic transition to a final SGTR phase that is globally quasi-stationary. The transition phase is dominated by a kink instability of a large “cat-eye” flux rope and the proliferation of a broad stochastic layer. The reconnection layer has two general characteristic thickness scales, which correlate with the reconnection rate and differ by a factor of approximately six: an inner scale corresponding with current and vorticity densities, turbulent fluctuations, and outflow jets, and an outer scale associated with field line stochasticity. The effective thickness of the reconnection layer is the inner scale of the effective reconnection electric field produced by turbulent fluctuations, not the stochastic thickness. The dynamics within the reconnection layer are closely linked with flux rope structures that are highly topologically complicated. Explorations of the flux rope structures and distinctive intermediate regions between the inner core and stochastic separatrices (“SGTR wings”) are potentially key to understanding SGTR. The study concludes with a discussion on the apparent dualism between plasmoid-mediated and stochastic perspectives on SGTR.

The Helicity Sign of Flux Transfer Event Flux Ropes and Its Relationship to the Guide Field and Hall Physics in Magnetic Reconnection at the Magnetopause

AbstractFlux Transfer Events (FTEs) are transient magnetic flux ropes typically found at the Earth's magnetopause on the dayside. While it is known that FTEs are generated by magnetic reconnection, it remains unclear how the details of magnetic reconnection controls their properties. A recent study showed that the helicity sign of FTEs positively correlates with the east‐west (By) component of the Interplanetary Magnetic Field (IMF). With data from the Cluster and Magnetospheric Multiscale missions, we performed a statistical study of 166 quasi force‐free FTEs. We focus on their helicity sign and possible association with upstream solar wind conditions and local magnetic reconnection properties. Using both in situ data and magnetic shear modeling, we find that FTEs whose helicity sign corresponds to the IMF By are associated with moderate magnetic shears while those that do not correspond to the IMF By are associated with higher magnetic shears. While uncertainty in IMF propagation to the magnetopause may lead to randomness in the determination of the flux rope core field and helicity, we rather propose that for small IMF By, which corresponds to high shear and low guide field, the Hall pattern of magnetic reconnection determines the FTE core field and helicity sign. In that context we explain how the temporal sequence of multiple X‐line formation and the reconnection rate are important in determining the flux rope helicity sign. This work highlights a fundamental connection between kinetic processes at work in magnetic reconnection and the macroscale structure of FTEs.

Acceleration of cold ions in magnetic reconnection

This paper describes the results of 2.5D particle-in-cell kinetic simulations of magnetic reconnection. We consider the case without cold ions (case 0) and with a cold ion flow loaded at two localized positions (cases 1 and 2). The cold ions are loaded on the lower side of the inflow region in cases 1 and 2: along the x-direction, the cold ions are centered at the x location of the X-line in case 1 and are positioned to one side in case 2. Our simulations suggest that cold ions are accelerated and heated near the upper separatrix region in both cases 1 and 2. The gyroradius of the orbit of cold ions increases in the diffusion region owing to the weak magnetic field and then enter the outflow region, where the cold ions pick up the E×B outflow. The cold ions are prevented from crossing the upper separatrix by the Hall electric field, which is negative at the upper exhaust region separatrix. The cold ions are accelerated along the negative z-direction in the upper inflow region by the nonideal electric field (E+vci×B)z for case 1. During this process, the cold ions undergo demagnetization drift association with the finite Larmor radius effect of cold ions. Yet, the reconnection rate decreases after the cold ions flow into the diffusion region. However, the magnetic reconnection rate exhibits no significant changes in case 2.

Storm‐Time Magnetopause: Pressure Balance

AbstractThe magnetopause is treated as a boundary where the pressure of the incoming solar wind is balanced by the pressure of the geomagnetic field and the plasma pressure inside the magnetopause is often neglected. However, published studies of pressure balance at the magnetopause reveal an excess of the magnetosheath pressure. Moreover, our survey of about 50,000 THEMIS magnetopause crossings shows that about 1% of them exhibits even larger magnetic field in the magnetosheath than in the magnetosphere. A subsequent analysis of crossings observed in the subsolar region under a southward interplanetary magnetic field shows the pressure of the dense cold ion population as an important component of the total magnetospheric pressure. This component is too cold to be registered by standard ion analyzers but its density can reach 300 cm−3. The second effect connected with a presence of cold plasma population is a reduction of the reconnection rate that slows down the transport of the magnetic flux down the tail and leads to magnetic pile‐up in the subsolar magnetosheath.

Effect of epicardial fat volume on outcomes after left atrial posterior wall isolation in addition to pulmonary vein isolation in patients with persistent atrial fibrillation.

Greater epicardial adipose tissue (EAT) is related to higher recurrences after atrial fibrillation catheter ablation (AFCA). We investigated the effects of posterior wall box isolation (POBI) in conjunction with circumferential pulmonary vein isolation (CPVI) on rhythm outcomes according to varying EAT volumes among patients with persistent atrial fibrillation (PeAF). We included 1,187 patients with PeAF undergoing a de novo AFCA including those receiving CPVI alone (n = 687) and those receiving additional POBI (n = 500). The rhythm outcomes at 2 years post-AFCA were compared in subgroups stratified by the EAT volume using propensity overlap weighting. A reduced EAT volume was linearly associated with more favorable rhythm outcomes for additional POBI than for CPVI alone (P for interaction = 0.002). Among the patients with smaller EAT volumes (≤116.23 mL, the median value, n = 594), additional POBI was associated with a reduced AF recurrence risk as compared to CPVI only [weighted HR (hazard ratio) 0.74, 95% CI (confidence interval) 0.56-0.99]. In contrast, among the remaining 593 patients with greater EAT volumes (>116.23 mL), No difference was observed in the recurrence risk between the additional POBI and CPVI alone groups (weighted HR 1.13, 95% CI 0.84-1.52). Among 205 patients with repeat ablations, the POBI reconnection rate was more frequent in the large EAT group (77.4%) than in the small EAT group (56.7%, P = 0.034). While PeAF patients with a smaller EAT volume averted AF recurrence by additional POBI after CPVI, no benefit of the POBI was observed in those with a greater EAT volume.

Calculating the Electron Diffusion Region Aspect Ratio With Magnetic Field Gradients

AbstractWe calculate the aspect ratio of the electron diffusion region (EDR) during symmetric magnetic reconnection using magnetic field gradients measured by the Magnetospheric Multiscale (MMS) Mission. The technique introduced in this paper is validated using a particle‐in‐cell simulation and used to calculate the EDR aspect ratios for three MMS‐observed magnetotail EDRs which are compared with the EDR aspect ratio predicted by scaling dependencies on asymptotic upstream electron β. We then use the aspect ratio to calculate the normalized reconnection rate and show that it is within uncertainty of the normalized reconnection rate found by previous studies for three MMS‐observed EDRs. Because the magnetic field gradients are velocity‐frame independent and typically very well measured by MMS, the technique can be used to obtain the normalized reconnection rate with higher fidelity than established methods.