Tilting Instability of Magnetically Confined Spheromaks

Abstract

We consider the tilting instability of a magnetically confined spheromak using 3D MHD and relativistic PIC calculations with an application to astrophysical plasmas, specifically those occurring in magnetar magnetospheres. The instability is driven by the counter alignment of the spheromak's intrinsic magnetic dipole with the external magnetic field. Initially the spheromak rotates - tilts - trying to lower its magnetic potential energy. As a result a current sheet forms between the internal magnetic field of a spheromak and the confining field. Magnetic reconnection sets in; this leads to the annihilation of the newly counter-aligned magnetic flux of the spheromak. This occurs on few Alfvén time scales. In the case of higher order (second order) spheromak, the internal core is first pushed out of the envelope, resulting in formation of two nearly independent tilting spheromaks. Thus, the magnetically twisted outer shell cannot stabilize the inner core. During dissipation, helicity of the initial spheromak is carried away by torsional Alfvén waves, violating the assumptions of the Taylor relaxation theorem. In applications to magnetars' giant flares, fast development of tilting instabilities, and no stabilization of the higher order spheromaks, make it unlikely that trapped spheromaks are responsible for the tail emission lasting hundreds of seconds.

arXiv comment20 pages, 10 figures, accepted for publication in Journal of Plasma Physics

References in corpus (13)

• PLUTO: a Numerical Code for Computational Astrophysics
• Magnetars
• The Evolution and Structure of Pulsar Wind Nebulae
• Gamma-Ray Observations of a Giant Flare from The Magnetar SGR 1806-20
• The Giant Flare of 1998 August 27 from SGR 1900+14: II. Radiative Mechanism and Physical Constraints on the Source
• Explosive reconnection in magnetars
• The electromagnetic model of Gamma Ray Bursts
• The first giant flare from SGR 1806-20: observations with the INTEGRAL SPI Anti-Coincidence Shield
• Tearing instability in relativistic magnetically dominated plasmas
• Structure of magnetic fields in intracluster cavities
• Coronal mass ejections as expanding force-free structures
• Nonideal evolution of nonaxisymmetric, force-free magnetic fields in a magnetar
• Toroidal equilibria in spherical coordinates

Cited by in corpus (2)

• The spheromak tilting and how it affects modelling coronal mass ejections
• Relativistic magnetic explosions