Nulls, subpulse drift and mode switching in pulsars: the polar-cap surface

Little attention has so far been paid to the division of the observed population between pulsars of the two spin directions that are possible. Almost all pulsars with positive corotational charge density at the polar caps are expected to satisfy space-charge-limited flow boundary conditions. Charge separation by blackbody photoelectric transitions in moving ions limits the acceleration potential, analogously with the more usually considered pair creation. However, the limitation is more severe so that proton and ion energies can be relativistic but not ultrarelativistic, and these allow the growth of Langmuir-mode-induced turbulence that couples directly with the radiation field, as shown by Asseo, Pelletier & Sol. The consequences of this, and of the several possible physical states of the polar cap, are described, qualitatively, as possible explanations for the complex phenomena of nulls, subpulse drift and mode switching observed in subsets of pulsars.