Ion beam apparatus provides beam blanking by utilizing an aperture through which the beam passes during unblanked periods, and elements for deflecting the beam during blanking so that the beam is deflected away from the aperture. Electrodes between the aperture element and the deflecting elements generate a potential exceeding the kinetic energy of charged particles emitted from the aperture element due to ions striking the aperture element during blanking. Charged particles emitted from the aperture element are thus prevented from striking the beam deflecting elements, thereby reducing hydrocarbon cracking, insulator accumulation, and charge accumulation on the deflecting elements. Beam stability is thereby enhanced. Charged particles emitted from the aperture element are also returned to the aperture element, so that an accurate measure of ion beam current is obtained by measuring current flow to the aperture element.