DE2623207

A novel method and apparatus for achieving electrostatic deflection of high current ion beams within a scanning apparatus. In one embodiment, a pair of gates are provided, with one gate being oriented proximate each side of the deflection plates, and each gate being biased to a negative voltage of a sufficient amplitude to repel electrons which otherwise would be attracted to the positively-biased deflection plates to thereby protect the electron cloud from degradation, and maintain space charge neutralization of the ion beam. In another embodiment, means are provided to drive the deflection plates at negative voltages at all times and to maintain portions of the ground tube of the apparatus adjacent the deflection plates at a ground or negative level in order to avoid degradation of the electron sheath.