Patent ID: 7247863

Claim:
A method for rapidly controlling the rate of ion generation in an ion source having a filament-cathode and a mirror electrode within walls of a chamber, the filament-cathode and the mirror electrode being opposed along a first direction without intervening structure, the ion source being operable to generate an ion beam from the ionization of an ion precursor gas present in the chamber by electrons emitted from the filament-cathode, the method comprising the steps of: applying a first potential to a positive end of the filament-cathode, relative to a potential at a negative end of the filament-cathode; applying a second potential to the walls of the chamber, relative to the potential at the negative end of the filament-cathode; controlling the potential of the mirror electrode between the potential at the negative end of the filament-cathode and the second potential, to control the number of electrons available for ionization; and emitting the ion beam from the chamber in a second direction that is generally perpendicular to the first direction.