MAGNETIC RECONNECTION IN PLASMAS

A review of the present status of the theory of magnetic reconnection is given. In strongly collisional plasmas reconnection proceeds via re sistive current sheets, i.e. quasi-stationary macroscopic Sweet-Parker sheets at intermediate values of the magnetic Reynolds number R-m, or mirco-current sheets in MHD turbulence, which develops at high R-m. I n hot, dilute plasmas the reconnection dynamics is dominated by nondis sipative effects, mainly the Hall term and electron inertia. Reconnect ion rates are found to depend only on the ion mass, being independent of the electron inertia and the residual dissipation coefficients. Sma ll-scale whistler turbulence is readily excited giving rise to an anom alous electron viscosity. Hence reconnection may be much more rapid th an predicted by conventional resistive theory.