Magnetic Field Lines Break Research Articles

Conversion of magnetic energy in the magnetic reconnection layer of a laboratory plasma.

Magnetic reconnection, in which magnetic field lines break and reconnect to change their topology, occurs throughout the universe. The essential feature of reconnection is that it energizes plasma particles by converting magnetic energy. Despite the long history of reconnection research, how this energy conversion occurs remains a major unresolved problem in plasma physics. Here we report that the energy conversion in a laboratory reconnection layer occurs in a much larger region than previously considered. The mechanisms for energizing plasma particles in the reconnection layer are identified, and a quantitative inventory of the converted energy is presented for the first time in a well-defined reconnection layer; 50% of the magnetic energy is converted to particle energy, 2/3 of which transferred to ions and 1/3 to electrons. Our results are compared with simulations and space measurements, for a key step towards resolving one of the most important problems in plasma physics.

Magnetic reconnection at the edge of Uranus's magnetic field

A new modeling study sheds light on how the magnetosphere of Uranus compares to those of other planets. Magnetospheres around the inner planets Mercury and Earth are primarily driven by the solar wind—the charged particles spewed out from the Sun—through magnetic reconnection, in which the planet's magnetic field lines break and reconnect, releasing energy in the process.

Magnetic reconnection from a multiscale instability cascade

Magnetic reconnection, the process whereby magnetic field lines break and then reconnect to form a different topology, underlies critical dynamics of magnetically confined plasmas in both nature and the laboratory. Magnetic reconnection involves localized diffusion of the magnetic field across plasma, yet observed reconnection rates are typically much higher than can be accounted for using classical electrical resistivity. It is generally proposed that the field diffusion underlying fast reconnection results instead from some combination of non-magnetohydrodynamic processes that become important on the 'microscopic' scale of the ion Larmor radius or the ion skin depth. A recent laboratory experiment demonstrated a transition from slow to fast magnetic reconnection when a current channel narrowed to a microscopic scale, but did not address how a macroscopic magnetohydrodynamic system accesses the microscale. Recent theoretical models and numerical simulations suggest that a macroscopic, two-dimensional magnetohydrodynamic current sheet might do this through a sequence of repetitive tearing and thinning into two-dimensional magnetized plasma structures having successively finer scales. Here we report observations demonstrating a cascade of instabilities from a distinct, macroscopic-scale magnetohydrodynamic instability to a distinct, microscopic-scale (ion skin depth) instability associated with fast magnetic reconnection. These observations resolve the full three-dimensional dynamics and give insight into the frequently impulsive nature of reconnection in space and laboratory plasmas.

New detail on auroral processes

High‐resolution imaging from spacecraft is revealing new detail on structures in bright, dynamic auroras. In the auroral regions where particles are accelerated to high energies, dynamic structures evolve on time scales of seconds or less, although the processes that drive particle acceleration and transfer of energy to small scales are not fully understood. Chaston et al. show how new spaceborne auroral imagery combined with simultaneous particle measurements can help improve understanding of the physical processes involved in the aurora. In particular, they show how magnetic reconnection (in which magnetic field lines break and reconnect, releasing energy), tearing, and sheared flows can transfer energy from larger to smaller scales and help form the auroral structures observed. (Geophysical Research Letters, doi:10.1029/2011GL049185, 2011)

Research Spotlight: Magnetic island observed at Earth's magnetopause

Understanding processes in the Earth's magnetosphere can help scientists understand and predict space weather and its effects on technology such as satellites and communications and navigation systems. Magnetic reconnection, in which magnetic field lines break, rearrange, and rejoin each other, is an important process that converts magnetic field energy into thermal and kinetic energy in the space plasma environment.

Dynamics and waves near multiple magnetic null points in reconnection diffusion region

Identifying the magnetic structure in the region where the magnetic field lines break and how reconnection happens is crucial to improving our understanding of three‐dimensional reconnection. Here we show the in situ observation of magnetic null structures in the diffusion region, the dynamics, and the associated waves. Possible spiral null pair has been identified near the diffusion region. There is a close relation among the null points, the bipolar signature of the Z component of the magnetic field, and enhancement of the flux of energetic electrons up to 100 keV. Near the null structures, whistler‐mode waves were identified by both the polarity and the power law of the spectrum of electric and magnetic fields. It is found that the angle between the fans of the nulls is quite close to the theoretically estimated maximum value of the group‐velocity cone angle for the whistler wave regime of reconnection.

Experimental onset threshold and magnetic pressure pile-up for 3D reconnection

Magnetic reconnection—the process by which magnetic field-lines break and reform in a plasma—is believed to be an important part of many astrophysical phenomena, but is poorly understood. The recreation of 3D reconnection events in a laboratory plasma provides a powerful means of studying the parameters that govern the onset, evolution and decay of this process.

Slipping Magnetic Reconnection in Coronal Loops

Magnetic reconnection of solar coronal loops is the main process that causes solar flares and possibly coronal heating. In the standard model, magnetic field lines break and reconnect instantaneously at places where the field mapping is discontinuous. However, another mode may operate where the magnetic field mapping is continuous but shows steep gradients: The field lines may slip across each other. Soft x-ray observations of fast bidirectional motions of coronal loops, observed by the Hinode spacecraft, support the existence of this slipping magnetic reconnection regime in the Sun's corona. This basic process should be considered when interpreting reconnection, both on the Sun and in laboratory-based plasma experiments.

Compressible dynamics of magnetic field lines for incompressible magnetohydrodynamic flows

It is demonstrated that the deformation of magnetic field lines in incompressible magnetohydrodynamic flows results from a compressible mapping associated with the transverse motion of fluid particles. Appearance of zeros for the Jacobian of this mapping corresponds to the breaking of magnetic field lines and the local blowup of the magnetic field intensity. The occurrence of such events is found to be unlikely in two dimensions but possible in three dimensions.