  We propose that the violent breakdown of the Ruderman-Sutherland type vacuum
gap above the pulsar polar cap region may produce copious primary particles and
make the charge density above the gap in excess of the Goldreich-Julian
density. Such an excess residue of charge density may arise some
re-acceleration regions above the gap due to the space-charge-limited flow
mechanism. Such re-acceleration regions, if exist, may accelerate particles to
carry away more spin-down energy, and may have some implications for pulsar
$\gamma$-ray emission.
