Faraday cup

The direct measurement of ion currents collected by a shielded electrode, called a Faraday cup, became possible in the 1930s with the introduction of electrometer tubes capable of measuring currents below a nanoampere, although sensitive galvanometers had been used for larger currents. The…

…in a device called a Faraday cup. Once in this collector, the current carried by the atoms is measured as it leaks across a resistor to ground. Currents measured are small, from only 10⁻¹¹ to 10⁻¹⁵ ampere, so that shielding and preamplification are required as close to the Faraday cup…