Novel Faraday cup for the simultaneous observation and measurement of ion-beam currents

A novel Faraday cup is described which allows the simultaneous observation and measurement of ion-beam currents. The Faraday cup is constructed around a Galileo channel electron multiplier array (CEMA), which serves as the basis of an internal image intensification system (a gain of ≳10⁴) for the observation of the ion beam; the CEMA also acts as a collector for the ion current which is measured by a Keithley 602 electrometer. The ion current is integrated by a simple and inexpensive dosimeter; the electronic circuit for the dosimeter is described. The application of the Faraday cup to the observation and measurement of a 30-keV Ar⁺ ion beam is presented as an illustrative example. We have also employed this Faraday cup to observe and measure 30-keV Cr⁺, Mo⁺, or W⁺, and 18-keV Au⁺ ion beams employed for the in situ irradiation of field-ion microscope specimens.