Observation of negative ions of cesium from thermionic converters and in desorption from metal surfaces

The flux from an 'open' thermionic converter is analyzed by molecular beam sampling and electron impact mass spectrometry. Both singly and doubly positively charged ions are normally observed, even without any electron emission in the ion source. The flux from a hot foil surface of iridium, with cesium diffusing through the foil, is studied in another type of experiment. It is shown to give large positive or negative currents to a collector, depending on the voltage of a grid closely located in front of the collector. Both experiments give strong evidence for the existence of multiply-excited, neutral and negative Rydberg states of Cs in the flux.