On the explosive phase of the tearing mode in double current sheet plasmas: effect of the equilibrium magnetic configuration on the onset threshold and growth rate. (arXiv:2107.10069v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Baty_H/0/1/0/all/0/1">Hubert Baty</a>
Magnetic reconnection associated with the tearing instability occurring in
double-current sheet systems is investigated within the framework of reduced
resistive magnetohydrodynamics (MHD) in a two-dimensional Cartesian geometry.
The explosive non linear phase is particularly explored using the adaptive
finite-element FINMHD code. The critical aspect ratio, that is defined as the
minimum $L/x_s$ ratio (with $L$ and $x_s$ being the system length and
half-distance between the two current layers respectively) necessary for non
linear destabilization after the linear and early non linear saturation phases,
is obtained. The latter threshold is independent of the details of the chosen
initial equilibrium (double Harris-like magnetic profile) and of the
resistivity. Its value is shown to be $4.7$, that is close and slightly smaller
than the value of order $5$ deduced using a more particular equilibrium
configuration in previous studies. The time dependence of the kinetic energy
($E_K$) is shown to follow a double exponential law, $E_K propto exp
[e^{(gamma^* t)} ]$, with a pseudo-growth rate $gamma^* simeq 0.1 t_A^
{-1}$ ($t_A$ being the characteristic Alfv’en time) that is again independent
of the configuration and resistivity. The mechanism offers a possible
explanation for the sudden onset of explosive magnetic energy release occurring
on the fast Alfv’en time scale in disruptive events of astrophysical plasmas
with pre-existing double current sheets like in the solar corona.
Magnetic reconnection associated with the tearing instability occurring in
double-current sheet systems is investigated within the framework of reduced
resistive magnetohydrodynamics (MHD) in a two-dimensional Cartesian geometry.
The explosive non linear phase is particularly explored using the adaptive
finite-element FINMHD code. The critical aspect ratio, that is defined as the
minimum $L/x_s$ ratio (with $L$ and $x_s$ being the system length and
half-distance between the two current layers respectively) necessary for non
linear destabilization after the linear and early non linear saturation phases,
is obtained. The latter threshold is independent of the details of the chosen
initial equilibrium (double Harris-like magnetic profile) and of the
resistivity. Its value is shown to be $4.7$, that is close and slightly smaller
than the value of order $5$ deduced using a more particular equilibrium
configuration in previous studies. The time dependence of the kinetic energy
($E_K$) is shown to follow a double exponential law, $E_K propto exp
[e^{(gamma^* t)} ]$, with a pseudo-growth rate $gamma^* simeq 0.1 t_A^
{-1}$ ($t_A$ being the characteristic Alfv’en time) that is again independent
of the configuration and resistivity. The mechanism offers a possible
explanation for the sudden onset of explosive magnetic energy release occurring
on the fast Alfv’en time scale in disruptive events of astrophysical plasmas
with pre-existing double current sheets like in the solar corona.
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