Production of Negative Ions and Noise in Negative Ion Beams

In a search for high current sources of low energy ({≈}100 ev) negative atomic ions of hydrogen and oxygen, five types of sources were examined. The most promising practical source for both H^- and O^- was found to be the dc glow discharge from which beams of 10^-7 ampere of either ion could be drawn. Hot cathode arc discharges yielded H^- currents of 7×{}10^-8 ampere. Rf discharges, hollow cathode discharges, and sources involving the Arnot effect seem inferior as high current sources.Two results were found which are of interest both for the mechanism of the discharge and for the production of negative ions. First, the most copious source of negative ions seems to be the anode side of well-formed striations such as are present in the two superior sources. Second, when either of these sources is used, the beam noise in the low audiofrequency range is much greater than shot noise and is related to fluctuations in the striations.