  Radio pulsars exhibit an enormous diversity of single pulse behaviour that
involves sudden changes in pulsation mode and nulling occurring on timescales
of tens or hundreds of spin periods. The pulsations appear both chaotic and
quasi-regular, which has hampered their interpretation for decades. Here I show
that the pseudo-chaotic complexity of single pulses is caused by the viewing of
a relatively simple radio beam that has a sector structure traceable to the
magnetospheric charge distribution. The slow ExB drift of the sector beam, when
sampled by the line of sight, produces the classical drift-period-folded
patterns known from observations. The drifting azimuthal zones of the beam
produce the changes in pulsation modes and both the intermodal and sporadic
nulling at timescales of beating between the drift and the star spin. The
axially symmetric conal beams are thus a superficial geometric illusion, and
the standard carousel model of pulsar radio beams does not apply. The beam
suggests a particle flow structure that involves inward motions with possible
inward emission.
