Magnetic reconnection

Magnetic reconnection is a physical process occurring in electrically conducting <a href="/facts/Plasma_(physics)/1d3btMVU">plasmas</a>, in which the <a href="/facts/Magnetic_topology/C0cVwHfl">magnetic topology</a> is rearranged and magnetic energy is converted to <a href="/facts/Kinetic_energy/aJRxUd4p">kinetic energy</a>, <a href="/facts/Thermal_energy/eVaKAC7K">thermal energy</a>, and <a href="/facts/Particle_acceleration/gRHpkT4v">particle acceleration</a>. Magnetic reconnection involves plasma flows at a substantial fraction of the <a href="/facts/Alfv%25C3%25A9n_wave/t1xtbVuf">Alfvén wave</a> speed, which is the fundamental speed for mechanical information flow in a magnetized plasma.
The concept of magnetic reconnection was developed in parallel by researchers working in solar physics and in the interaction between the solar wind and magnetized planets. This reflects the bidirectional nature of reconnection, which can either disconnect formerly connected magnetic fields or connect formerly disconnected magnetic fields, depending on the circumstances.
<a href="/facts/Ron_Giovanelli/q9ABV7dY">Ron Giovanelli</a> is credited with the first publication invoking magnetic energy release as a potential mechanism for <a href="/facts/Particle_acceleration/gRHpkT4v">particle acceleration</a> in <a href="/facts/Solar_flare/6kCvPKxD">solar flares</a>. Giovanelli proposed in 1946 that solar flares stem from the energy obtained by charged particles influenced by induced <a href="/facts/Electric_field/tt4MooBs">electric fields</a> within close proximity of <a href="/facts/Sunspot/7E8cWSGl">sunspots</a>. In the years 1947-1948, he published more papers further developing the reconnection model of solar flares. In these works, he proposed that the mechanism occurs at points of neutrality (weak or null magnetic field) within structured magnetic fields.
<a href="/facts/James_Dungey/5J4HoFQC">James Dungey</a> is credited with first use of the term “magnetic reconnection” in his 1950 PhD thesis, to explain the coupling of mass, energy and momentum from the <a href="/facts/Solar_wind/BvuB3dT8">solar wind</a> into Earth's <a href="/facts/Magnetosphere/BXzgPoPy">magnetosphere</a>. The concept was published for the first time in a seminal paper in 1961. <a href="/facts/James_Dungey/5J4HoFQC">Dungey</a> coined the term "reconnection" because he envisaged field lines and plasma moving together in an inflow toward a magnetic neutral point (2D) or line (3D), breaking apart and then rejoining again but with different magnetic field lines and plasma, in an outflow away from the magnetic neutral point or line. 
In the meantime, the first theoretical framework of magnetic reconnection was established by <a href="/facts/Peter_Alan_Sweet/ADgG7zfN">Peter Sweet</a> and <a href="/facts/Eugene_Parker/WxoeHcVp">Eugene Parker</a> at a conference in 1956. Sweet pointed out that by pushing two plasmas with oppositely directed magnetic fields together, resistive diffusion is able to occur on a length scale much shorter than a typical equilibrium length scale. Parker was in attendance at this conference and developed scaling relations for this model during his return travel.

Magnetic reconnection open-in-new

Magnetic reconnection