  The origin of pulsar radio emission is one of the old puzzles in theoretical
astrophysics. In this Letter we present a global kinetic plasma simulation
which shows from first-principles how and where radio emission can be produced
in pulsar magnetospheres. We observe the self-consistent formation of electric
gaps which periodically ignite electron-positron discharge. The gaps form above
the polar-cap, and in the bulk return-current. Discharge of the gaps excites
electromagnetic modes which share several features with the radio emission of
real pulsars. We also observe the excitation of plasma waves and charge bunches
by streaming instabilities in the outer magnetosphere. Our numerical experiment
demonstrates that global kinetic models can provide deep insight into the
emission physics of pulsars, and may help interpret their multi-wavelength
observations.
