Trajectory analysis of ions formed in the field emitter inter-electrode region

Ion trajectories are three-dimensionally analyzed to determine the main source of ions striking the emitting area of a field emitter. Computer calculations of the ion trajectories are made for a field emitter in the shape of a sphere radius 1000 Å, mounted on an orthogonal cone, and anode radii of 3 cm and 1 cm centered at the emitter. Approximately 10^?10 to 10^?9fraction of the ions formed at the anode by electron impact desorption reach the emitter tip. Only those residual gas ions generated in the space of a few μm around the tip are able to impinge on the emitting area. Under typical operating conditions of 10^?9 Torr, the residual gas ions striking the tip are 10 to 10² times greater than those from the anode, assuming an ion ejection of one ion per 10⁵ electrons, and an anode potential of about 3 kV.