Magnetic X-point Research Articles

Resistive modes at a magnetic X-point

The characteristic time of (incompressible) resistive modes in the neighbourhood of an X-point in the absence of external forcing is found to scale, when normalized on the Alfven time, as ( epsilon mod ln epsilon mod )-1 with epsilon the ratio between the Alfven and the resistive time. In X-point configurations with oblique separatrices, the mode time-scale becomes faster as the angle between the separatrices decreases. When this angle becomes of the order of mod ln epsilon mod -1, the ( epsilon mod ln epsilon mod )-1 scaling breaks down. Similar to the case of a resonant magnetic line configuration, resistive modes can be driven unstable by the inhomogeneity of the current density.

A theory of filament eruptions before the impulsive phase of solar flares

We present a theory of filament eruption before the impulsive phase of solar flares. We show that the upward motion of the magnetic X-point tracing the filament eruption begins several minutes before the impulsive phase of the flare, where the explosive magnetic reconnection starts at the X-point magnetic field configuration located under the filament. No change occurs in the character of the motion of the X-point during the onset of the explosive magnetic reconnection. The upward speed of the X-point is about 110 km s-1 at the onset of the impulsive phase. We give an important condition leading to filament eruptions, which relate to the state of the current sheet under the filament, where the magnetic energy can be released.

The dynamics of the energetic proton bursts in the course of the magnetic field topology reconstruction in the earth‘s magnetotail

The paper considers the energy spectrum of particles accelerated near X-point of the magnetic field in the course of the tearing instability development in the current layer. The time dynamics of the spectrum at the linear and nonlinear stages of the instability is studied. The contribution of the particles inflowing into the vicinity of the magnetic X-point due to drift in the crossed electrical and magnetic fields was also taken into account. The dynamics of particle acceleration is numerically simulated and the results of the simulation are compared with the theoretical model. The analytical and numerical calculations are in reasonable agreement with the results of IMP satellites 7 and 8 energetic proton measurements in a wide energy interval.

Nonlinear evolution of the sheet pinch

An incompressible, dissipative numerical code of the spectral type is used to follow the nonlinear evolution of a magnetohydrodynamic sheet pinch in two spatial dimensions. The evolution involves considerable turbulent activity in the electric current field, with the excited spatial scales ranging from the size of the containing volume down to the dissipation lengths of the magnetic and velocity fields. Strong current filamentation near magnetic X-points is observed, as is lsquo;jetting’, or expulsion of magnetofluid from the vicinity of the X-point parallel to the current sheet.