The Faraday cup consists of a hollow stainless steel cylinder
closed at the base, with an appropriately-sized aperture for
collecting the electrons or ions. An outer, grounded cylinder
provides shielding. An electrical connection is made to the base
of the Faraday cup, terminating in a BNC. The current is then
conducted to a vacuum feedthrough and so to an ammeter.
The Faraday cup can be electrically biased to reduce
scattering of electrons or ions collected in the Faraday cup
and to reduce secondary electron emission. For electrons or
negative ions, +50 V is typically adequate, and for positive
ions, 50 V. This can be accomplished by placing a battery
between the vacuum feedthrough and the ammeter.