  We perform first-principles relativistic particle-in-cell simulations of
aligned pulsar magnetosphere. We allow free escape of particles from the
surface of a neutron star and continuously populate the magnetosphere with
neutral pair plasma to imitate pair production. As pair plasma supply
increases, we observe the transition from a charge-separated electrosphere
solution with trapped plasma and no spin-down to a solution close to the ideal
force-free magnetosphere with electromagnetically-dominated pulsar wind. We
calculate the magnetospheric structure, current distribution and spin-down
power of the neutron star. We also discuss particle acceleration in the
equatorial current sheet.
