  The destabilization mechanism of the collisional microtearing mode driven by
an electron temperature gradient is studied using theoretical analyses and
gyrokinetic simulations including a comprehensive collision model, in
magnetized slab plasmas. The essential destabilization mechanism of the
microtearing mode is the lag of the parallel inductive electric field behind
the magnetic field owing to the time-dependent thermal force and inertia force
induced by the velocity-dependent electron--ion collisions. Quantitative
measurements of the collision effects enable us to identify the unstable regime
against collisionality and reveal the relevance of the collisional microtearing
mode with existing toroidal experiments. A nonlinear simulation demonstrates
that the microtearing mode does not drive magnetic reconnection with the
explosive release and conversion of the magnetic energy.
