Ion Source for Low-Energy Negative Ions

A negative ion source is described which is capable of producing negative ion beams of moderate intensity, but with relatively narrow spread in ion energy. The source consists essentially of a jet of gas intersected by an electron beam. The pressure in the vicinity of the thermionic electron source is kept low by differential pumping. Although ion currents are not as high as those obtained with discharge sources, the present source produces ion beams particularly free of noise and instability.