The central plasma sheet (CPS) is simulated as a 1D cellular automaton. The system is driven deterministically and globally by a spatially non-uniform energy loading (convection). Each node (a flux tube) evolves until one of two local instability criteria is exceeded. The unstable node releases a small amount of energy to the ionosphere and another small amount is distributed to its neighboring nodes. The partition between the two modes of energy distribution is the only random factor in the model. The energy redistribution relaxes the node deterministically to a stable state. The simulation suggests that a central plasma sheet driven in the above manner is in a self-organized critical state, with energy avalanches obeying a scale-free distribution. The avalanches, however, co-exist with quasi-periodic intermittencies manifested in ring-current injection, which is correlated with strong CPS avalanches, and tailward energy ejection, which shows no apparent correlation in this aspect.