Current sheet equilibrium selection via relaxation and dynamo processes

From the Harris equilibrium to the force-free equilibrium, there is a continuous spectrum of 1D kinetic current sheet equilibria. However, only a select few solutions, notably those at each end of the spectrum, are readily being used for analyses of magnetized plasma phenomena such as magnetic reconnection. This limited usage is rather unjustified given the infinite number of mixed equilibria, and arises from our lack of understanding of the current sheet equilibrium selection process. Here we show how a particular equilibrium is selected by a given system, by revealing the equilibration process of an initially disequilibrated current sheet with a finite guide field. The initial current sheet equilibrates in a way that entails a dynamo process in which the seed guide field is locally amplified, eventually yielding a mixed equilibrium. The ubiquity of such equilibria is demonstrated by comparing particle-in-cell simulations to spacecraft observations.