Simple on-line method of measuring the absolute ionization efficiency of an ion source

We report a new method of measuring the absolute ionization efficiency of an ion source, which is independent of gas flow rate fed to an ionizer and of the detection efficiency of the resulting ions. The method is based on the fact that when a pulsed alternating potential is applied between the ionizer and an electrode placed outside near its exit hole, ions stored inside the ionizer when the potential is repulsive for the ions, are flushed out as soon as it becomes attractive. It is shown that when the duty factor and repetition rate of the applied potential are properly chosen, the magnitude of this bunching effect can simply be expressed only by the ionization efficiency. Since its magnitude can quickly be evaluated, for example by observing the time dependence of the bunched ion current in an oscilloscope, it provides a simple and reliable way for on-line diagnostics of the source.