EMISSION CURRENT DEPENDENCE IN THE TIME AND ANGLE NOISE SPECTRA OF GALLIUM LIQUID METAL ION SOURCES

Abstract
The frequency and inverse angular power spectra of the emission of ions from a gallium liquid metal ion source has been studied as a fonction of emission current using an ion streak camera. The camera records the angle and time of arrival of individual ions with a chevron multichannel plate detector. Results indicate that the previously reported decrease in fluctuation power with increasing angular wave number is present at all emission currents between 5 and 75 µA and becomes only slightly more pronounced with increasing source current. There is also a distinct rolloff in fluctuation power with increasing frequency above 200 Mhz, the slope of this rolloff increasing slightly with increasing source current. The total power in the fluctuations is roughly proportional to the axial current density from the source. At emission currents greater that 100 µA the emission of individual droplets is evident as "shadows" in the angle-time images. The shapes of these shadows are influenced both by droplet size and charge.