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 Io n Source (LMIS) equipped with condenser lens optics. This device consi sts of two subsequent electrostatic x-y-deflection units, each followe d 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 uni t 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 generate d 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 L MIS system was determined in a single measurement. From this data the projected two-dimensional distributions I(x,x') and I(y,y') could be d erived. The resulting brightness values behind the extraction optics a nd condenser lens of the source were calculated. It could be shown tha t beam brightness is significantly reduced after passing the extractio n 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 ext rapolated value for beam current of 2 pA is approximate to 6 x 10(4) A m(-2)rad(-2)eV(-1). (C) 1998 Elsevier Science B.V.