Negative Oxygen Ions from a Glow Discharge Source

A simple source of O - ions suitable for accelerator applications is described. Negative atomic ion currents of over 2 μA can be directly extracted at 10 keV energy for a low-pressure cold-cathode oxygen discharge source which incorporates an electrostatic constrictor electrode. The input power is only 25 watts and the gas consumption 14 cm 3 h -1 of oxygen at atmospheric pressure. Mass analysis of the beam has shown the primary components to be O - and O 2 - ions whilst the main impurity ions are OH - , Cl - and NO 2 - . A study has been made of the relationship between the negative ion yield and various source operating conditions. The O - and O 2 - ion yields are shown to be related to the striated structure of the positive column. With a singly striated column the beam is composed mainly of atomic ions. Only when a doubly striated column is formed does the O 2 - yield become large. Ion production processes are discussed in terms of this relationship.