Thermodynamic Phase Transition in Magnetic Reconnection

By examining the entropy production in fully kinetic simulations of collisional plasmas, it is shown that the transition from collisional Sweet-Parker reconnection to collisionless Hall reconnection may be viewed as a thermodynamic phase transition. The phase transition occurs when the reconnection electric field satisfies E = E-D root m(e)/m(i), where m(e)/m(i) is the electron-to-ion mass ratio and E-D is the Dreicer electric field. This condition applies for all m(i)/m(e), including m(i)/m(e) = 1, where the Hall regime vanishes and a direct phase transition from the collisional to the kinetic regime occurs. In the limit m(e)/m(i) -> 0, this condition is equivalent to there being a critical electron temperature T-e approximate to m(i)Omega(2)(i)delta(2), where Omega(i) is the ion cyclotron frequency and delta is the current sheet half-thickness. The heat capacity of the current sheet changes discontinuously across the phase transition, and a critical power law is identified in an effective heat capacity. A model for the time-dependent evolution of an isolated current sheet in the collisional regime is derived.

Automated summary

Through examining entropy production in fully kinetic simulations of collisional plasmas, it is shown that the transition from collisional Sweet-Parker reconnection to collisionless Hall reconnection can be viewed as a thermodynamic phase transition. A specific condition for the phase transition is identified, where the reconnection electric field satisfies a particular equation. During the phase transition, the heat capacity of the current sheet undergoes a discontinuous change, and a critical power law is observed in the effective heat capacity.