Why does Steady-State Magnetic Reconnection have a Maximum Local Rate of Order 0.1?

Liu, Yi‐Hsin; Hesse, Michael; Guo, Fan; Daughton, W.; Li, H.; Cassak, P. A.; Shay, M. A.

doi:10.1103/physrevlett.118.085101

Cited by 153 publications

(228 citation statements)

References 63 publications

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“…In the following, we are going to justify this assumption, to draw the consequences and to show that our results fit the results of Ref. [66] and justify (27). Our discussion is qualitative; then, the operator '=' refers to order-of-magnitude-estimates only in the following.…”

Section: More About (27)mentioning

confidence: 98%

“…In spite of the huge uncertaintiespossibly due to both large measurement errors [3], insufficient computational resources for realistic problems, and far-from-complete understading of magnetic reconnection -this comparison seems to confirm our result, qualitatively at least. Finally, we discuss a possible connection among (11), (27) and the results of [61], [66], [67] and [68] in Appendix C .…”

Section: Merging Vs Bouncingmentioning

confidence: 99%

“…[66] (where M A is dubbed 'local reconnection rate'): M A is a complicated function of the geometry of the magnetic field lines, but its maximum is a quite broad one -i.e., near the maximum M A depends very weakly on the detailed geometry of field lines. Of course, the motion of the merging plasmoids modifies the geometry of the field lines.…”

Section: More About (27)mentioning

confidence: 99%

“…This is a long-standing puzzle of reconnection physics. For a long time now, observations in a wide variety of settings -including reconnection events in solar flares, geomagnetic substorms and sawtooth crashes in magnetically confined fusion devices [65] [66] [67] -have suggested that…”

Section: Merging Vs Bouncingmentioning

confidence: 99%

“…|B| is the absolute value of the inflow speed. The normalizing value of |B|c A in M A is taken asymptotically far from the ('micro-scale') region ruled by magnetic diffusion [66], rather than immediately upstream of it. Now, it comes to the merging.…”

Section: Merging Vs Bouncingmentioning

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: More About (27)mentioning

confidence: 98%

Section: Merging Vs Bouncingmentioning

confidence: 99%

Section: More About (27)mentioning

confidence: 99%

Section: Merging Vs Bouncingmentioning

confidence: 99%

Section: Merging Vs Bouncingmentioning

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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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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Scaling the Ion Inertial Length and Its Implications for Modeling Reconnection in Global Simulations

et al. 2017

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We investigate the use of artificially increased ion and electron kinetic scales in global plasma simulations. We argue that as long as the global and ion inertial scales remain well separated, (1) the overall global solution is not strongly sensitive to the value of the ion inertial scale, while (2) the ion inertial scale dynamics will also be similar to the original system, but it occurs at a larger spatial scale, and (3) structures at intermediate scales, such as magnetic islands, grow in a self‐similar manner. To investigate the validity and limitations of our scaling hypotheses, we carry out many simulations of a two‐dimensional magnetosphere with the magnetohydrodynamics with embedded particle‐in‐cell (MHD‐EPIC) model. The PIC model covers the dayside reconnection site. The simulation results confirm that the hypotheses are true as long as the increased ion inertial length remains less than about 5% of the magnetopause standoff distance. Since the theoretical arguments are general, we expect these results to carry over to three dimensions. The computational cost is reduced by the third and fourth powers of the scaling factor in two‐ and three‐dimensional simulations, respectively, which can be many orders of magnitude. The present results suggest that global simulations that resolve kinetic scales for reconnection are feasible. This is a crucial step for applications to the magnetospheres of Earth, Saturn, and Jupiter and to the solar corona.

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Why does Steady-State Magnetic Reconnection have a Maximum Local Rate of Order 0.1?

Cited by 153 publications

References 63 publications

On super-elastic collisions between magnetized plasmoids in the heliosphere

On super-elastic collisions between magnetized plasmoids in the heliosphere

On the Collisionless Asymmetric Magnetic Reconnection Rate

Scaling the Ion Inertial Length and Its Implications for Modeling Reconnection in Global Simulations

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