Crisis in the periodic Lorentz gas.
The attractor of the nonequilibrium Lorentz gas covers the whole of the accessible phase space at small values of the field. Here we investigate the transition from this state to a state with fractal support, corresponding to a discontinuity in the box dimension as a function of field. A number of numerical techniques are employed, the most effective involving symbolic dynamics. It is found that above the transition, the dynamics is effectively irreversible in a manner not evident below the transition. A similar crisis occurs at different spacings and rotation angles. @S1063-651X~96!10111-2#