(Color online) A phase diagram for magnetic reconnection in two dimensions. If either S or the normalized size, λ, is small, reconnection with a single X-line occurs in collisional or in collisionless phases. When both S and λ are sufficiently large, three new multiple X-line phases appear with magnetic islands. The dynamics of new current sheets between these islands are determined either by collisional physics or by collisionless physics (see Secs.III and IV.). The conditions for electron runaway are shown as red lines (see Sec. V). The locations for reconnection in Earth’s magnetosphere, solar corona, solar chromosphere, and solar tachocline are also shown. The existing experiments, such as MRX, do not have access to these new phases. A NGRX is required for such accesses to these new phases directly relevant to reconnection in heliophysical and astrophysical plasmas.
(Color online) In the regimes of high Lundquist number and large plasma size, the plasmoid instability gives rise to a hierarchy of interacting current sheets and islands. The above sketch gives the notation used here for describing this hierarchy.
(Color online) The phase diagram in a smaller parameter space to show dotted and dashed lines better (see texts in Sec. III). Other symbols are same as in Fig. 1.
(Color) Results from a kinetic simulation (Ref. 65) of guide field reconnection showing the formation and interaction of flux ropes as illustrated by an isosurface of the particle density colored by the magnitude of the current density along with sample magnetic field lines (yellow). Simulation parameters are m i /m e = 100 with the initial guide field equal to the reconnecting field. The domain size is 70d i × 70d i × 35d i corresponding to 2048 × 2048 × 1024 cells and ∼1012 particles.
(Color online) Various laboratory, heliophysical, and astrophysical plasmas, in which magnetic reconnection is believed to occur, are shown in the phase diagram. Other symbols are same as in Fig. 1. See the text and Table I for details.
Key parameters of various plasmas from laboratory, heliophysics, and astrophysics. Unless explicitly stated, assumptions are (1) , (2) the reconnecting field is 1/10 of total magnetic field, B R = 0.1B T , (3) equal electron and ion temperatures, T e = T i , and (4) ions are protons. We note that there are opinions that the plasmas in Crab pulsar wind and radio lobes are nonthermal so that temperature may not be a good description (Refs. 68 and 69). There are some laboratory experiments which are not listed: flux rope experiments (Refs. 70–72) with S ∼λ∼ 101 and plasma merging experiments (Refs. 73 and 74) with S = 102–103 and λ = 101–102.
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