On the value of the reconnection rate

Comisso, Luca; Bhattacharjee, A.

doi:10.1017/s002237781600101x

Cited by 67 publications

(57 citation statements)

References 65 publications

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“…In spite of the uncertainties -due to both large measurement errors, insufficient computational resources for realistic problems, and far-from- [67] and assume the value of the global reconnection rate to be ≈ 0.1. This value does not depend on S, in contrast with the predictions of Sweet and Parker's and Petschek's models of reconnection.…”

Section: Discussionmentioning

confidence: 99%

“…of (26), this is equivalent to say that we expect (26) still to hold when shock waves are present, but with a somewhat larger value of v thr : if shocks are present, then merging is more difficult. Indeed, the value of M A may strongly differ from 0.1 if compressibility plays a role [67].…”

Section: B Comparison Of (26) and (27) With Available Datamentioning

confidence: 99%

“…In spheromak-like plasmas we write Ω P J d 3 x = Ω E · jd 3 x ∝ Ω E · Bd 3 x ≈ (∆Φ) · E // ds where E // ds is computed on a magnetic field line and its maximum value (on the field lines) is ∝ Moreover, the model of [66] provides no explicit dependence of M A on S. In contrast, Sweet and Parker's model gives M A = S − 1 2 , and Petschek's model predicts that the maximum value of M A is equal to π 8 ln S . However, both Sweet and Parker's and Petschek's models are steady state models; but in a reconnection layer dominated by the presence of plasmoids, the complexity of the dynamics gives rise to a strongly time-dependent process [67]. If S is small enough, then the maximum value of M A predicted by these models exceeds the constant value of M A in (27).…”

Section: More About (27)mentioning

confidence: 99%

“…If these assumptions are violated, as e.g. in compressible plasmas where shock waves are present [3], then different values of M A are expected [67]). The qualitative nature of our arguments may justify the discrepancy.…”

Section: More About (27)mentioning

confidence: 99%

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On super-elastic collisions between magnetized plasmoids in the heliosphere

Vita

2018

Eur. Phys. J. D

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Recently, a unique collision between two large-scale magnetized plasmoids produced by coronal mass ejections in the heliosphere has been observed [C. Shen et al., Nature Physics 8, 923-928 (2012)]. Results suggest that the collision is super-elastic, i.e. the total linear kinetic energy of the two plasmoids after the collision is larger than before the collision, and that an anti-correlation exists, i.e. the lower the initial relative velocity of the plasmoids, the larger the relative increase in total kinetic energy. The problemCoronal mass ejections (CMEs) give birth to large-scale plasmoids, originating from the solar atmosphere and expanding and propagating into the heliosphere [1] [2]. The occurrence rate of CMEs is about 4-5 CMEs per day at solar maximum [3], so that encounters and interactions between plasmoids are unavoidable. Nevertheless, inter-plasmoid collisions are far from understood. While collisions between blobs of ordinary gases are heavily affected by mixing, cross-field diffusion is effectively prohibited by sufficiently strong magnetic field.Experiments show that initially well-distinct plasmoids preserve their identity after a collision; historically, these experiments led to the very definition of 'plasmoid' as a 'plasma magnetic entity' with well-distinguished identity and geometrical structure [4]. In the lab, conventional magnetohydrodynamics fails to provide adequate macroscopic description of isolated plasmoids [5] -let alone their mutual interaction. In space, such description requires detailed knowledge of energy balance and state equation [2].Recent observation of a collision between plasmoids [1] suggests that such collisions may be superelastic, i.e. the total linear kinetic energy of the colliding plasmoids after the collision is larger than before the collision. A similar phenomenon is observed in collisions of spheres with elastoplastic plates, where rotational kinetic energy may be transferred into linear kinetic energy [6]. This analogy suggests that the linear kinetic energy in collisions between plasmoids may increase at the expense of the energy of some other degree of freedom, and magnetic energy is an obvious candidate. A preliminary investigation of energy balance supports this point of view; moreover, it has been suggested that the lower the impact velocity, the larger the relative increase of the linear kinetic energy [1]; in contrast, if the relative velocity of colliding plasmoids is too large, then no elastic scattering occurs [7], and the plasmoids may merge into each other.The aim of this work is to investigate this suggestion. We invoke the analogy [8] between plasmoids in the lab and space plasmoids and show how recent progress [5] [9] in the analytical description of the former provide information on the latter. In particular, we show that quantities usually invoked in Hall MHD [10] lead to a simple macroscopic description of interacting plasmoids. Some relevant properties of our plasmoids are discussed in Sec. 2. Secs. 3 and 4 discuss the structure...

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Section: Discussionmentioning

confidence: 99%

Section: B Comparison Of (26) and (27) With Available Datamentioning

confidence: 99%

Section: More About (27)mentioning

confidence: 99%

Section: More About (27)mentioning

confidence: 99%

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On super-elastic collisions between magnetized plasmoids in the heliosphere

Vita

2018

Eur. Phys. J. D

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“…Therefore, a Sweet-Parker regime is often a misnomer when describing reconnection processes occurring in the Sun's corona, since the inflows from the surroundings of the reconnection region are not themselves steady state. How the reconnection rate is actually determined by boundary conditions is still poorly understood (see the discussions in Comisso & Bhattacharjee 2016). Recently, Forbes et al (2013), Baty et al (2014) have argued that the rate of reconnection is more likely to be controlled by the non-uniformity of the normal magnetic field in reconnecting layers rather than by the boundary conditions.…”

Section: Current Layer Formation and Evolutionmentioning

confidence: 99%

Three-dimensional magnetic reconnection and its application to solar flares

Janvier

2017

J. Plasma Phys.

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Solar flares are powerful radiations occurring in the Sun's atmosphere. They are powered by magnetic reconnection, a phenomenon that can convert magnetic energy into other forms of energy such as heat and kinetic energy, and which is believed to be ubiquitous in the universe. With the ever increasing spatial and temporal resolutions of solar observations, as well as numerical simulations benefiting from increasing computer power, we can now probe into the nature and the characteristics of magnetic reconnection in three dimensions to better understand the phenomenon's consequences during eruptive flares in our star's atmosphere. We review in the following the efforts made on different fronts to approach the problem of magnetic reconnection. In particular, we will see how understanding the magnetic topology in three dimensions helps in locating the most probable regions for reconnection to occur, how the current layer evolves in three dimensions and how reconnection leads to the formation of flux ropes, plasmoids and flaring loops.

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On the Collisionless Asymmetric Magnetic Reconnection Rate

Liu

Hesse

Cassak

et al. 2016

Geophysical Research Letters

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A prediction of the steady state reconnection electric field in asymmetric reconnection is obtained by maximizing the reconnection rate as a function of the opening angle made by the upstream magnetic field on the weak magnetic field (magnetosheath) side. The prediction is within a factor of 2 of the widely examined asymmetric reconnection model (Cassak & Shay, 2007, https://doi.org/10.1063/1.2795630) in the collisionless limit, and they scale the same over a wide parameter regime. The previous model had the effective aspect ratio of the diffusion region as a free parameter, which simulations and observations suggest is on the order of 0.1, but the present model has no free parameters. In conjunction with the symmetric case (Liu et al., 2017, https://doi.org/10.1103/PhysRevLett.118.085101), this work further suggests that this nearly universal number 0.1, essentially the normalized fast‐reconnection rate, is a geometrical factor arising from maximizing the reconnection rate within magnetohydrodynamic‐scale constraints.

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On the value of the reconnection rate

Cited by 67 publications

References 65 publications

On super-elastic collisions between magnetized plasmoids in the heliosphere

On super-elastic collisions between magnetized plasmoids in the heliosphere

Three-dimensional magnetic reconnection and its application to solar flares

On the Collisionless Asymmetric Magnetic Reconnection Rate

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