Implosive collapse about magnetic null points

A quantitative comparison between 2D and 3D nulls

Jonathan Thurgood (Lead / Corresponding author), David Pontin, James A. McLaughlin

Research output: Contribution to journalArticle

3 Citations (Scopus)
83 Downloads (Pure)

Abstract

Null collapse is an implosive process whereby MHD waves focus their energy in the vicinity of a null point, forming a current sheet and initiating magnetic reconnection. We consider, for the first time, the case of collapsing 3D magnetic null points in nonlinear, resistive MHD using numerical simulation, exploring key physical aspects of the system as well as performing a detailed parameter study. We find that within a particular plane containing the 3D null, the plasma and current density enhancements resulting from the collapse are quantitatively and qualitatively as per the 2D case in both the linear and nonlinear collapse regimes. However, the scaling with resistivity of the 3D reconnection rate - which is a global quantity - is found to be less favorable when the magnetic null point is more rotationally symmetric, due to the action of increased magnetic back-pressure. Furthermore, we find that, with increasing ambient plasma pressure, the collapse can be throttled, as is the case for 2D nulls. We discuss this pressure-limiting in the context of fast reconnection in the solar atmosphere and suggest mechanisms by which it may be overcome. We also discuss the implications of the results in the context of null collapse as a trigger mechanism of Oscillatory Reconnection, a time-dependent reconnection mechanism, and also within the wider subject of wave-null point interactions. We conclude that, in general, increasingly rotationally asymmetric nulls will be more favorable in terms of magnetic energy release via null collapse than their more symmetric counterparts.

Original languageEnglish
Article number50
Pages (from-to)1-15
Number of pages15
JournalAstrophysical Journal
Volume855
Issue number1
DOIs
Publication statusPublished - 7 Mar 2018

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trigger mechanism
plasma
plasma pressure
solar atmosphere
current sheets
plasma density
energy
comparison
electrical resistivity
actuators
current density
scaling
augmentation
atmosphere
simulation
interactions
rate
parameter

Keywords

  • Sun: flares
  • Sun: oscillations
  • magnetic reconnection
  • magnetohydrodynamics (MHD)
  • plasmas
  • shock waves

Cite this

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title = "Implosive collapse about magnetic null points: A quantitative comparison between 2D and 3D nulls",
abstract = "Null collapse is an implosive process whereby MHD waves focus their energy in the vicinity of a null point, forming a current sheet and initiating magnetic reconnection. We consider, for the first time, the case of collapsing 3D magnetic null points in nonlinear, resistive MHD using numerical simulation, exploring key physical aspects of the system as well as performing a detailed parameter study. We find that within a particular plane containing the 3D null, the plasma and current density enhancements resulting from the collapse are quantitatively and qualitatively as per the 2D case in both the linear and nonlinear collapse regimes. However, the scaling with resistivity of the 3D reconnection rate - which is a global quantity - is found to be less favorable when the magnetic null point is more rotationally symmetric, due to the action of increased magnetic back-pressure. Furthermore, we find that, with increasing ambient plasma pressure, the collapse can be throttled, as is the case for 2D nulls. We discuss this pressure-limiting in the context of fast reconnection in the solar atmosphere and suggest mechanisms by which it may be overcome. We also discuss the implications of the results in the context of null collapse as a trigger mechanism of Oscillatory Reconnection, a time-dependent reconnection mechanism, and also within the wider subject of wave-null point interactions. We conclude that, in general, increasingly rotationally asymmetric nulls will be more favorable in terms of magnetic energy release via null collapse than their more symmetric counterparts.",
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Implosive collapse about magnetic null points : A quantitative comparison between 2D and 3D nulls. / Thurgood, Jonathan (Lead / Corresponding author); Pontin, David; McLaughlin, James A.

In: Astrophysical Journal, Vol. 855, No. 1, 50, 07.03.2018, p. 1-15.

Research output: Contribution to journalArticle

TY - JOUR

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T2 - A quantitative comparison between 2D and 3D nulls

AU - Thurgood, Jonathan

AU - Pontin, David

AU - McLaughlin, James A.

N1 - The authors acknowledges generous support from the Leverhulme Trust and this work was funded by a Leverhulme Trust Research Project Grant: RPG-2015-075. The authors acknowledge IDL support provided by STFC. The computational work for this paper was carried out on HPC facilities provided by the Faculty of Engineering and Environment, Northumbria University, UK.

PY - 2018/3/7

Y1 - 2018/3/7

N2 - Null collapse is an implosive process whereby MHD waves focus their energy in the vicinity of a null point, forming a current sheet and initiating magnetic reconnection. We consider, for the first time, the case of collapsing 3D magnetic null points in nonlinear, resistive MHD using numerical simulation, exploring key physical aspects of the system as well as performing a detailed parameter study. We find that within a particular plane containing the 3D null, the plasma and current density enhancements resulting from the collapse are quantitatively and qualitatively as per the 2D case in both the linear and nonlinear collapse regimes. However, the scaling with resistivity of the 3D reconnection rate - which is a global quantity - is found to be less favorable when the magnetic null point is more rotationally symmetric, due to the action of increased magnetic back-pressure. Furthermore, we find that, with increasing ambient plasma pressure, the collapse can be throttled, as is the case for 2D nulls. We discuss this pressure-limiting in the context of fast reconnection in the solar atmosphere and suggest mechanisms by which it may be overcome. We also discuss the implications of the results in the context of null collapse as a trigger mechanism of Oscillatory Reconnection, a time-dependent reconnection mechanism, and also within the wider subject of wave-null point interactions. We conclude that, in general, increasingly rotationally asymmetric nulls will be more favorable in terms of magnetic energy release via null collapse than their more symmetric counterparts.

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KW - Sun: flares

KW - Sun: oscillations

KW - magnetic reconnection

KW - magnetohydrodynamics (MHD)

KW - plasmas

KW - shock waves

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JO - Astrophysical Journal

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