Due to the electron-gas collision ionization in a FED, positively charged ions bombard the cathode. This can destroy the field emitters and cause instabilities. In this study we have selected a normal-gate sub-cell to calculate the ion bombardment (IB). In the cases of uniform emitting and ring emitting, the process of ion bombardment and cathode damage has been investigated. (c) 2004 Published by Elsevier B.V.