A new broad-beam alkali ion source for use in ultra high vacuum

A new broad-beam ion source of alkali (K+) ions for use in ultra high vacuum was designed, built and tested. The basic principles used have advantages over gas-fed broad-beam ion sources, because there is no need for differential pumping, and because an intrinsically pure ion beam obviates the necessity for charge-to-mass analysis. The source is based on the effect of thermionic emission of K+ ions from solid potassium aluminosilicate (K2O . Al2O3 . 2SiO(2)) emitter. An ion beam current of 0.4 mA has been achieved at an extraction voltage of 3.5 kV with 1.5 cm beam diameter. The degassed broad-beam ion source in operation does not appreciably influence the background pressure in the ultra high vacuum system.