On plasma rotation and drifting subpulses in pulsars; using aligned
  pulsar B0826-34 as a voltmeter
  We derive the exact drift velocity of plasma in the pulsar polar cap, in
contrast to the order-of-magnitude expressions presented by Ruderman &
Sutherland (1975) and generally used throughout the literature. We emphasize
that the drift velocity depends not on the absolute value, as is generally
used, but on the variation of the accelerating potential across the polar cap.
If we assume that drifting subpulses in pulsars are indeed due to this plasma
drift, several observed subpulse-drift phenomena that are incompatible with the
Ruderman & Sutherland family of models can now be explained: we show that
variations of drift rate, outright drift reversals, and the connection between
drift rates and mode changes have natural explanations within the frame of the
"standard" pulsar model, when derived exactly. We apply this model for drifting
subpulses to the case of PSR B0826-34, an aligned pulsar with two separate
subpulse-drift regions emitted at two different colatitudes. Careful
measurement of the changing and reversing drift rate in each band independently
sets limits on the variation of the accelerating potential drop. The derived
variation is small, ~10^{-3} times the vacuum potential drop voltage. We
discuss the implications of this result for pulsar modeling.
