This study of the magnetotail employs a large-scale kinetic ion model specifically developed to consider the region's approach to equilibrium and its dynamics under the influence of an imposed electric field. Results from the self-consistent, two-dimensional model indicate that the magnetotail achieves equilibrium by maintaining a delicate balance between the influx of plasma from a mantle source and the accelerated loss of these particles resulting from nonadiabatic particle dynamics. The quasi-steady oscillations that result from instantaneous imbalances between sources and losses occur independent of solar wind variations. This variability occurs even for steady solar wind conditions and is caused by the rapid nonadiabatic energization of ions incident on the current sheet and their loss through the flanks of the magnetotail faster than they can be replenished. To determine the influence of external parameters on the dynamical state of the magnetotail, we performed a parameter search in which we varied the magnitude of the convection electric field and the influx of plasma mantle ions. This parameter search showed that the magnetotail configuration can adjust itself to compensate for the various combinations of solar wind parameters. As a rule, this self-adjustment occurs in the form of quasi-steady magnetotail states, where only the average characteristics of the configuration are steady but pronounced cyclic variations occur in the magnetotail topology. For cases in which the magnetotail is underpopulated, the current sheet is depleted via the flanks. In overpopulation cases a flaring of magnetotail field lines caused by the additional current in the neural sheet limits access of additional mantle particles to the region. The magnetotail system is flexible enough to self-consistently regulate its own population. However, the resulting configuration becomes dynamic and only a quasi-steady state is achieved. ¿ 2000 American Geophysical Union