Role of Z-pinches in magnetic reconnection in space plasmas

Olshevsky, Vyacheslav; Lapenta, Giovanni; Divin, Andrey

doi:10.1017/s0022377814000725

Cited by 6 publications

(13 citation statements)

References 40 publications

(40 reference statements)

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“…Pressure imbalance is a trigger for the initial explosive relaxation of the system. During this phase, half of the magnetic energy is converted to the particle energy (Olshevsky et al 2015b). The second stage of the evolution is characterized by randomly distributed, turbulent dissipation events taking place all over the domain.…”

Section: Results: "Multiple Nulls"mentioning

confidence: 99%

“…Further investigation has indicated that spiral magnetic nulls and current filaments exhibited strong energy dissipation and magnetic reconnection signatures. In contrast, energy dissipation events at the radial nulls were rather short-living and localized (Olshevsky et al 2015a(Olshevsky et al , 2015b. These findings motivated us to perform this survey of magnetic nulls in other kinetic simulations of space plasmas.…”

Section: Introductionmentioning

confidence: 97%

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Magnetic Null Points in Kinetic Simulations of Space Plasmas

Olshevsky

Deca

Divin

et al. 2016

ApJ

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We present a systematic attempt to study magnetic null points and the associated magnetic energy conversion in kinetic particle-in-cell simulations of various plasma configurations. We address three-dimensional simulations performed with the semi-implicit kinetic electromagnetic code iPic3D in different setups: variations of a Harris current sheet, dipolar and quadrupolar magnetospheres interacting with the solar wind,and a relaxing turbulent configuration with multiple null points. Spiral nulls are more likely created in space plasmas: in all our simulations except lunar magnetic anomaly (LMA) and quadrupolar mini-magnetosphere the number of spiral nulls prevails over the number of radial nulls by a factor of 3-9. We show that often magnetic nulls do not indicate the regions of intensive energy dissipation. Energy dissipation events caused by topological bifurcations at radial nulls are rather rare and short-lived. The so-called X-lines formed by the radial nulls in the Harris current sheet and LMA simulations are rather stable and do not exhibit any energy dissipation. Energy dissipation is more powerful in the vicinity of spiral nulls enclosed by magnetic flux ropes with strong currents at their axes (their crosssections resemble 2D magnetic islands). These null lines reminiscent of Z-pinches efficiently dissipate magnetic energy due to secondary instabilities such as the two-stream or kinking instability, accompanied by changes in magnetic topology. Current enhancements accompanied by spiral nulls may signal magnetic energy conversion sites in the observational data.

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Section: Results: "Multiple Nulls"mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Magnetic Null Points in Kinetic Simulations of Space Plasmas

Olshevsky

Deca

Divin

et al. 2016

ApJ

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“…The simulation data in this study are from Olshevsky et al [, ], who initiate magnetic reconnection at Ω ci t = 0 and terminate it at Ω ci t = 52. The two snapshots we investigate are at the middle (Ω ci t = 26) and final (Ω ci t = 52) stages of the simulation.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…In theory [ Greene , ; Lau and Finn , ] and simulations [ Galsgaard and Pontin , ; Olshevsky et al , , ], the properties and topology of magnetic nulls have been well studied. Generally, the null topology consists of a spine and a fan [ Priest and Titov , ; Parnell et al , ] and can have both “radial” and “spiral” features.…”

Section: Introductionmentioning

confidence: 99%

“…We therefore suggest using this method to find magnetic nulls and reconstruct field topology with four-point measurements, particularly from Cluster and the forthcoming MMS mission. For the MMS mission, this null-finding algorithm can be used to trigger its burst-mode measurements.In theory [Greene, 1988;Lau and Finn, 1990] and simulations [Galsgaard and Pontin, 2011;Olshevsky et al, 2013Olshevsky et al, , 2015, the properties and topology of magnetic nulls have been well studied. Generally, the null topology consists of a spine and a fan [Priest and Titov, 1996;Parnell et al, 1996] and can have both "radial" and "spiral" features.…”

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How to find magnetic nulls and reconstruct field topology with MMS data?

et al. 2015

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In this study, we apply a new method—the first‐order Taylor expansion (FOTE)—to find magnetic nulls and reconstruct magnetic field topology, in order to use it with the data from the forthcoming MMS mission. We compare this method with the previously used Poincare index (PI), and find that they are generally consistent, except that the PI method can only find a null inside the spacecraft (SC) tetrahedron, while the FOTE method can find a null both inside and outside the tetrahedron and also deduce its drift velocity. In addition, the FOTE method can (1) avoid limitations of the PI method such as data resolution, instrument uncertainty (Bz offset), and SC separation; (2) identify 3‐D null types (A, B, As, and Bs) and determine whether these types can degenerate into 2‐D (X and O); (3) reconstruct the magnetic field topology. We quantitatively test the accuracy of FOTE in positioning magnetic nulls and reconstructing field topology by using the data from 3‐D kinetic simulations. The influences of SC separation (0.05~1 di) and null‐SC distance (0~1 di) on the accuracy are both considered. We find that (1) for an isolated null, the method is accurate when the SC separation is smaller than 1 di, and the null‐SC distance is smaller than 0.25~0.5 di; (2) for a null pair, the accuracy is same as in the isolated‐null situation, except at the separator line, where the field is nonlinear. We define a parameter ξ ≡ |( λ1 + λ2 + λ3 )|/|λ|max in terms of the eigenvalues (λi) of the null to quantify the quality of our method—the smaller this parameter the better the results. Comparing to the previously used parameter (η≡|∇ ⋅ B|/|∇ × B|), ξ is more relevant for null identification. Using the new method, we reconstruct the magnetic field topology around a radial‐type null and a spiral‐type null, and find that the topologies are well consistent with those predicted in theory. We therefore suggest using this method to find magnetic nulls and reconstruct field topology with four‐point measurements, particularly from Cluster and the forthcoming MMS mission. For the MMS mission, this null‐finding algorithm can be used to trigger its burst‐mode measurements.

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Methods for Finding Magnetic Nulls and Reconstructing Field Topology

Wang

Zong

et al. 2020

Geophysical Monograph Series

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Role of Z-pinches in magnetic reconnection in space plasmas

Cited by 6 publications

References 40 publications

Magnetic Null Points in Kinetic Simulations of Space Plasmas

Magnetic Null Points in Kinetic Simulations of Space Plasmas

How to find magnetic nulls and reconstruct field topology with MMS data?

Methods for Finding Magnetic Nulls and Reconstructing Field Topology

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