Coalescence Instability in the Electron Magnetohydrodynamics

The relaxation of a magnetic field perturbation periodic in two directions is studied in the electron magnetohydrodynamic approximation. It is shown that the relaxation is accompanied by the coalescence of magnetic cells. When transport coefficients are sufficiently low, the nonlinear stage of the coalescence process is independent of their values. This effect may help to explain why the duration of the crash phase of sawtooth oscillations in tokamaks is anomalously short.