An emittance scanning device for liquid metal ion sources

A new emittance scanning device has been developed to investigate the phase space emittance distribution of a 30 keV-Gallium Liquid Metal Ion Source (LMIS) equipped with condenser lens optics. This device consists of two subsequent electrostatic x-y-deflection units, each followed by a fixed pinhole aperture (10...50 mu m diameter): The first unit selects a lateral element of the ion beam (x(i), y(i)); the second unit selects an angular element (x(i)'; y(i)'), The beam current on both apertures is measured by current integration. The beam intensity I(x(i),y(i),x(i)',y(i)') transmitted through both apertures is monitored by a channeltron detector via the number of secondary electrons generated on a beam stop. Beam profile measurements using this device yielded direct information on system alignment, condenser lens properties and beam halo. The four-dimensional trace-space intensity profile of the LMIS system was determined in a single measurement. From this data the projected two-dimensional distributions I(x,x') and I(y,y') could be derived. The resulting brightness values behind the extraction optics and condenser lens of the source were calculated. It could be shown that beam brightness is significantly reduced after passing the extraction system and condenser lens. For a beam current of 100 pA a brightness of >100 Am(-2)rad(-2)eV(-1) was observed, while the corresponding extrapolated value for beam current of 2 pA is approximate to 6 x 10(4) Am(-2)rad(-2)eV(-1). (C) 1998 Elsevier Science B.V.