Observation of explosive collisionless reconnection in 3D nonlinear gyrofluid simulations

Biancalani, A.; Scott, B.

doi:10.1209/0295-5075/97/15005

Cited by 10 publications

(23 citation statements)

References 18 publications

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“…Because of the normalization assumed in these articles, the increase of the growth rates with decreasing plasma β implies for the linear growth rate a scaling

γ_{I} τ_{_{A}}^{*} \sim d_{e}

and for the nonlinear one a scaling

γ_{II} τ_{_{A}}^{*} \sim d_{e}^{0}

at fixed ρ s , thus suggesting (cf. equations and for p = 1) that an ideal tearing regime was observed in the nonlinear stage of the simulations discussed by Biancalani and Scott []. Future studies will elucidate whether the explosive reconnection predicted by equation and that studied in Biancalani and Scott [] are effectively the same phenomenon.…”

Section: Discussionmentioning

confidence: 85%

“…The above discussions demonstrate that the rescaling argument at the basis of ideal tearing may provide a fairly general paradigm to describe explosive growth rate increases. Consider now what is observed in the nonlinear stage of simulations of reconnection at L / a not much larger than unity [ Ali et al , ; Biancalani and Scott , ; Yu et al , ], when an X point collapses into two Y points and the current sheet between the two becomes tearing unstable, eventually leading to what has been interpreted as the plasmoid chain instability.…”

Section: Discussionmentioning

confidence: 94%

“…Of course, a more detailed analysis would be required to verify whether the rescaling argument summarized by equations and the corresponding threshold conditions for the ideal tearing suffice to explain the explosive reconnection regimes observed in the above mentioned numerical studies. However, the qualitative considerations about the scalings provided in Figure 3 of Biancalani and Scott [] and in Figure 2 of Biancalani and Scott [] seem encouraging. Because of the normalization assumed in these articles, the increase of the growth rates with decreasing plasma β implies for the linear growth rate a scaling

γ_{I} τ_{_{A}}^{*} \sim d_{e}

and for the nonlinear one a scaling

γ_{II} τ_{_{A}}^{*} \sim d_{e}^{0}

at fixed ρ s , thus suggesting (cf.…”

Section: Discussionmentioning

confidence: 99%

“…The large predicted growth rates and the presence of critical values for dimensionless numbers such as current sheet aspect ratio make the described instabilities good candidates to understand and model the mechanisms behind observed fast reconnection phenomena [ Velli et al , ]. Indeed, to date there is no agreed theoretical explanation for the fast time scales over which reconnection events develop in nature nor for their triggering, while evidence from both experiments and numerical simulations points to the importance of small‐scale formation and kinetic effects, [ Daughton et al , ; Moser and Bellan , ; Biancalani and Scott , ] which are theoretically expected to lead to Alfvénic (or “ideal”) reconnection in 3‐D configurations as well [ Boozer , ]. Moreover, numerical simulations of tearing mode instabilities have identified a secondary, nonlinear, increase of the reconnection rate that has been sometimes interpreted in terms of a nascent plasmoid‐unstable SP regime [ Loureiro et al , ; Ali et al , ] or generically a secondary “explosive reconnection” regime [ Biancalani and Scott , ].…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, to date there is no agreed theoretical explanation for the fast time scales over which reconnection events develop in nature nor for their triggering, while evidence from both experiments and numerical simulations points to the importance of small‐scale formation and kinetic effects, [ Daughton et al , ; Moser and Bellan , ; Biancalani and Scott , ] which are theoretically expected to lead to Alfvénic (or “ideal”) reconnection in 3‐D configurations as well [ Boozer , ]. Moreover, numerical simulations of tearing mode instabilities have identified a secondary, nonlinear, increase of the reconnection rate that has been sometimes interpreted in terms of a nascent plasmoid‐unstable SP regime [ Loureiro et al , ; Ali et al , ] or generically a secondary “explosive reconnection” regime [ Biancalani and Scott , ]. A nonlinear increase of the reconnection rate on ideal, Alfvénic time scales was also numerically measured by Yu et al [] in simulations of low mode number reconnection instabilities.…”

Section: Introductionmentioning

confidence: 99%

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“Ideal” tearing and the transition to fast reconnection in the weakly collisional MHD and EMHD regimes

et al. 2016

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This paper discusses the transition to fast growth of the tearing instability in thin current sheets in the collisionless limit where electron inertia drives the reconnection process. It has been previously suggested that in resistive MHD there is a natural maximum aspect ratio (ratio of sheet length and breadth to thickness) which may be reached for current sheets with a macroscopic length L, the limit being provided by the fact that the tearing mode growth time becomes of the same order as the Alfvén time calculated on the macroscopic scale. For current sheets with a smaller aspect ratio than critical the normalized growth rate tends to zero with increasing Lundquist number S, while for current sheets with an aspect ratio greater than critical the growth rate diverges with S. Here we carry out a similar analysis but with electron inertia as the term violating magnetic flux conservation: previously found scalings of critical current sheet aspect ratios with the Lundquist number are generalized to include the dependence on the ratio de2/L2, where de is the electron skin depth, and it is shown that there are limiting scalings which, as in the resistive case, result in reconnecting modes growing on ideal time scales. Finite Larmor radius effects are then included, and the rescaling argument at the basis of “ideal” reconnection is proposed to explain secondary fast reconnection regimes naturally appearing in numerical simulations of current sheet evolution.

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“…Because of the normalization assumed in these articles, the increase of the growth rates with decreasing plasma β implies for the linear growth rate a scaling

γ_{I} τ_{_{A}}^{*} \sim d_{e}

and for the nonlinear one a scaling

γ_{II} τ_{_{A}}^{*} \sim d_{e}^{0}

Section: Discussionmentioning

confidence: 85%

Section: Discussionmentioning

confidence: 94%

γ_{I} τ_{_{A}}^{*} \sim d_{e}

and for the nonlinear one a scaling

γ_{II} τ_{_{A}}^{*} \sim d_{e}^{0}

at fixed ρ s , thus suggesting (cf.…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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“Ideal” tearing and the transition to fast reconnection in the weakly collisional MHD and EMHD regimes

et al. 2016

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Gyrofluid analysis of electron β_e effects on collisionless reconnection

et al. 2022

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The linear and nonlinear evolutions of the tearing instability in a collisionless plasma with a strong guide field are analysed on the basis of a two-field Hamiltonian gyrofluid model. The model is valid for a low ion temperature and a finite $\beta _e$ . The finite $\beta _e$ effect implies a magnetic perturbation along the guide field direction, and electron finite Larmor radius effects. A Hamiltonian derivation of the model is presented. A new dispersion relation of the tearing instability is derived for the case $\beta _e=0$ and tested against numerical simulations. For $\beta _e \ll 1$ the equilibrium electron temperature is seen to enhance the linear growth rate, whereas we observe a stabilizing role when electron finite Larmor radius effects become more relevant. In the nonlinear phase, stall phases and faster than exponential phases are observed, similarly to what occurs in the presence of ion finite Larmor radius effects. Energy transfers are analysed and the conservation laws associated with the Casimir invariants of the model are also discussed. Numerical simulations seem to indicate that finite $\beta _e$ effects do not produce qualitative modifications in the structures of the Lagrangian invariants associated with Casimirs of the model.

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Numerical investigation of a compressible gyrofluid model for collisionless magnetic reconnection

et al. 2012

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International audienceIon Larmor radius effects on guide field collisionless magnetic reconnection are investigated by means of numerical simulations based on a gyrofluid model for compressible plasmas. Compressibility along the magnetic field is seen to favour the distribution of ion guiding center density along the neutral line, rather than along the separatrices, unlike the electron density. On the other hand, increasing ion temperature reduces the intensity of ion guiding flow that develop in the direction parallel to the magnetic guide field. Numerical simulations suggest that the width of these bar-shaped layers scale linearly with the ion Larmor radius. The increase of ion temperature radius causes also a reduction of the electron parallel velocity. As a consequence, it is found that the cusp-like profiles distinctive of non-dissipative reconnection are strongly attenuated. The field structures are interpreted in terms of the behavior of the four topological invariants of the system. Two of these are seen to behave similarly to invariants of simpler models that do not account for parallel ion flow. The other two exhibit different structures, partly as a consequence of the small electron/ion mass ratio. The origin of these invariants at the gyrokinetic level is also discussed. The investigation of the field structures is complemented by an analysis of the energetics of the system

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Observation of explosive collisionless reconnection in 3D nonlinear gyrofluid simulations

Cited by 10 publications

References 18 publications

“Ideal” tearing and the transition to fast reconnection in the weakly collisional MHD and EMHD regimes

“Ideal” tearing and the transition to fast reconnection in the weakly collisional MHD and EMHD regimes

Gyrofluid analysis of electron β_e effects on collisionless reconnection

Numerical investigation of a compressible gyrofluid model for collisionless magnetic reconnection

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Observation of explosive collisionless reconnection in 3D nonlinear gyrofluid simulations

Cited by 10 publications

References 18 publications

“Ideal” tearing and the transition to fast reconnection in the weakly collisional MHD and EMHD regimes

“Ideal” tearing and the transition to fast reconnection in the weakly collisional MHD and EMHD regimes

Gyrofluid analysis of electron β e effects on collisionless reconnection

Numerical investigation of a compressible gyrofluid model for collisionless magnetic reconnection

Contact Info

Product

Resources

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Gyrofluid analysis of electron β_e effects on collisionless reconnection