80 research outputs found
Generalized Magnetofluid Connections in Relativistic Magnetohydrodynamics
The concept of magnetic connections is extended to non-ideal relativistic
magnetohydrodynamical plasmas. Adopting a general set of equations for
relativistic magnetohydrodynamics including thermal-inertial, thermal
electromotive, Hall and current-inertia effects, we derive a new covariant
connection equation showing the existence of generalized magnetofluid
connections that are preserved during the dissipationless plasma dynamics.
These connections are intimately linked to a general antisymmetric tensor that
unifies the electromagnetic and fluid fields, allowing the extension of the
magnetic connection notion to a much broader concept.Comment: Accepted for publication in Physical Review Letter
Formation of Plasmoid Chains in Fusion Relevant Plasmas
The formation of plasmoid chains is explored for the first time within the
context of the Taylor problem, in which magnetic reconnection is driven by a
small amplitude boundary perturbation in a tearing-stable slab plasma
equilibrium. Numerical simulations of a magnetohydrodynamical model of the
plasma show that for very small plasma resistivity and viscosity, the linear
inertial phase is followed by a nonlinear Sweet-Parker evolution, which gives
way to a faster reconnection regime characterized by a chain of plasmoids
instead of a slower Rutherford phase
Extended theory of the Taylor problem in the plasmoid-unstable regime
A fundamental problem of forced magnetic reconnection has been solved taking
into account the plasmoid instability of thin reconnecting current sheets. In
this problem, the reconnection is driven by a small amplitude boundary
perturbation in a tearing-stable slab plasma equilibrium. It is shown that the
evolution of the magnetic reconnection process depends on the external source
perturbation and the microscopic plasma parameters. Small perturbations lead to
a slow nonlinear Rutherford evolution, whereas larger perturbations can lead to
either a stable Sweet-Parker-like phase or a plasmoid phase. An expression for
the threshold perturbation amplitude required to trigger the plasmoid phase is
derived, as well as an analytical expression for the reconnection rate in the
plasmoid-dominated regime. Visco-resistive magnetohydrodynamic simulations
complement the analytical calculations. The plasmoid formation plays a crucial
role in allowing fast reconnection in a magnetohydrodynamical plasma, and the
presented results suggest that it may occur and have profound consequences even
if the plasma is tearing-stable.Comment: Accepted for publication in Physics of Plasma
Gyro-induced acceleration of magnetic reconnection
The linear and nonlinear evolution of magnetic reconnection in collisionless
high-temperature plasmas with a strong guide field is analyzed on the basis of
a two-dimensional gyrofluid model. The linear growth rate of the reconnecting
instability is compared to analytical calculations over the whole spectrum of
linearly unstable wave numbers. In the strongly unstable regime (large \Delta
'), the nonlinear evolution of the reconnecting instability is found to undergo
two distinctive acceleration phases separated by a stall phase in which the
instantaneous growth rate decreases. The first acceleration phase is caused by
the formation of strong electric fields close to the X-point due to ion
gyration, while the second acceleration phase is driven by the development of
an open Petschek-like configuration due to both ion and electron temperature
effects. Furthermore, the maximum instantaneous growth rate is found to
increase dramatically over its linear value for decreasing diffusion layers.
This is a consequence of the fact that the peak instantaneous growth rate
becomes weakly dependent on the microscopic plasma parameters if the diffusion
region thickness is sufficiently smaller than the equilibrium magnetic field
scale length. When this condition is satisfied, the peak reconnection rate
asymptotes to a constant value.Comment: Accepted for publication on Physics of Plasma
Thermal-inertial effects on magnetic reconnection in relativistic pair plasmas
The magnetic reconnection process is studied in relativistic pair plasmas
when the thermal and inertial properties of the magnetohydrodynamical fluid are
included. We find that in both Sweet-Parker and Petschek relativistic scenarios
there is an increase of the reconnection rate owing to the thermal-inertial
effects, both satisfying causality. To characterize the new effects we define a
thermal-inertial number which is independent of the relativistic Lundquist
number, implying that reconnection can be achieved even for vanishing
resistivity as a result of only thermal-inertial effects. The current model has
fundamental importance for relativistic collisionless reconnection, as it
constitutes the simplest way to get reconnection rates faster than those
accessible with the sole resistivity.Comment: Accepted for publication in Physical Review Letters; 1 figure;
Relativistic plasma physic
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