Apparatus and method for producing ions

摘要

A source of a beam of ions includes in a housing a cathode filament, an anode spaced from the cathode and housing an ion emission opening therethrough and an intermediate electrode between the cathode and anode and having an opening therethrough in alignment with the opening in the anode. An inlet opening extends through the housing into the space between the anode and the intermediate electrode to admit a flow of starting gas and the gas to be ionized into the housing. An outlet opening is through the housing adjacent the cathode and a pump is connected to the outlet opening. In the operation of the ion source a flow of the starting gas is provided through the housing and over the cathode to initiate the discharge. Then the gas to be ionized is admitted into the housing. Some of the gas is ionized to generate the desired ions and the rest of the gas is drawn out of the housing to remove impurities generated at the cathode and thereby increase the lifetime of the cathode. Once the ionizing gas is admitted into the housing, the flow of the starting gas is stopped.