Transmission of keV O⁻ ions through a single tapered glass capillary

An experimental study of 14 keV O⁻ ions transmission through a tapered glass capillary with the inlet diameters of 580 μm, an outlet diameter of 68 μm and a length of 45 mm, has been performed in this work. It indicates that the O⁻ ions transmitting through the tapered capillary had a density enhancement of about 5.5 times with the tilt angle of 0°. It was found that more than 97% of the transmitted and focused ions remained their initial charge state in central area. It's the first time that focusing effect was observed and was reported in experiment for negative ions. The angular distribution of transmitted ions was narrow. These results clearly indicated that the focusing effect can be achieved in the transmission process of keV O⁻ ions through a tapered glass capillary.