Charge densities above pulsar polar caps

The ability of the neutron star surface to supply all or only part of the c harges filling the pulsar magnetosphere is crucial for the physics prevaili ng within it, with direct consequences for the possible formation of pair-c reation regions. We evaluate the conditions for e(-) emission from pulsar s urfaces for a simple Goldreich-Julian geometry taking both thermal and fiel d emission processes into account. Using recently published estimates for t he equation of state at the neutron star's surface, we show that, for a lar ge range of T-surf, B, and P, the liberated charges will fully screen the a ccelerating B-parallel electric field E-parallel to. For surface temperatur es T-surf < 2 x 10(5) K a balance between field emission of electrons and s hielding of the field will occur. Even in the overidealized case of T-surf = 0 one can expect a prodigious supply of electrons, which will weaken the accelerating E-<parallel>. We calculated the motion of electrons along sele cted polar field lines numerically for the low-temperature, field emission scenario yielding their Lorentz factors, as well as the produced radiation densities. Inverse Compton and later curvature losses are seen to balance t he acceleration by the residual electric fields. We found that the conditio ns for magnetic pair production are not met anywhere along the field lines up to a height of 1500 pulsar radii. We did not a priori assume an "inner g ap," and our calculations did not indicate the formation of one under reali stic physical conditions without the introduction of further assumptions.