A TOFMS study of excited cesium species from a thermal plasma device

Abstract

The flux of cesium species from a thermal cesium plasma is studied by time-of-flight mass spectrometry. Excited cesium species drift to an ionization region located in a separately pumped chamber. In this region some of the excited cesium species are field ionized by an electric field which has a field strength of 200 V cm −1 in the ionizing pulses. The ions formed are accelerated with less than 100 V into a flight path and are finally detected. Typical time-of-flight (TOF) mass spectra display two peaks. The first peak is due to Cs + formed from singly excited cesium atoms, and the second peak is due to cesium clusters with 5–15 cesium atoms which have fragmented to atomic ions in the flight path. The emission of excited species increases with increasing emitter saturation current, while it is generally quite low when the plasma shows a large back-current, i.e. in the mode with accumulation of Rydberg species and Rydberg matter in the thermionic energy converter (TEC).