Inner vacuum gap formation and drifting subpulses in pulsars

The problem of formation of the inner vacuum gap in neutron stars with $\mathbf{\Omega }\cdot \mathbf{B}<0$ is considered. It is argued by means of the condition $T_i\mathrm{/}{T}_s>1$, where $T_i$ is the melting temperature of surface ${}_{26}^{56}$Fe ions and $T_s$ is the actual temperature of the polar cap surface, that the inner vacuum gap can form, provided that the actual surface magnetic field is extremaly strong ($B_s\gtrsim {10}^{13}$ G) and curved (${\cal R}<10^6$ cm), irrespective of the value of dipolar component measured from the pulsar spin down rate. The calculations are carried out for pulsars with drifting subpulses and/or periodic intensity modulations, in which the existence of the quasi steady vacuum gap discharging via $\mathbf{E}\times \mathbf{B}$ drifting sparks is almost unavoidable.