Vacuum solid-state ion-conducting silver source for application in field emission electric propulsion systems

A point-like silver ion source with thin film of RbAg4I5 solid electrolyte was developed for application in field emission electric propulsion systems. The solid electrolyte produced by mechano-chemical synthesis was deposited on the apex of a silver tip using pulsed laser deposition. The running tests at 195 °C working temperature and 10 kV accelerating potential have demonstrated that the source can continuously produce positive ion current of several hundred pA during a few days with a peak value of 25–50 nA. Using TOF-SIMS analysis it has been shown that the ion current consists of Ag+ with a small contribution of Rb+, lower than 0.5 at.%. We suggest that Ag+ emission occurs mainly by means of field-assisted ion evaporation and/or ion desorption, and the solid electrolyte plays a role of the transport system, in which the emitted Ag+ ions are continually replaced by mobile Ag+ ions delivered from the silver reservoir by direct mass transfer under the influence of an external electric field.