On the tearing mode in quasi‐neutral sheets

For a quasi‐neutral current sheet with a finite normal magnetic component the tearing mode is stabilized by the adiabatic motion of the magnetized electrons. If the current sheet is not absolutely quiescent but contains electromagnetic wave turbulence (or collisions) which pitch angle scatters the mirror‐trapped electrons, the tearing mode is destabilized with a growth rate proportional to the pitch angle diffusion coefficient. For observed turbulence levels in the earth's plasma sheet the tearing growth time could be 5 min.