Investigation of emission instabilities of liquid metal ion sources

Ion emission instabilities have been investigated using simultaneously taken current oscillograms and frequency spectra, for Ga, AuGe and AuGeSi liquid metal ion sources (LMISs). The current fluctuation intensity depends nonlinearly on emission current: it displays an S-like shape and tends towards saturation at currents of 70–80 μA in the case of Ga. The saturation value of the mean fluctuation amplitude (rms) is ∼5 μA about the d.c. level for this source. For alloy sources the emitter temperature was varied between 400 and 1060 °C; the onset for the appearance of current fluctuations – indicative of electrohydrodynamic instabilities at the liquid anode – varied with temperature. Moreover, it was found that with increasing temperature a LMIS becomes increasingly unstable. The experimental results are supported by existing theory.