Faraday Cups
A Faraday cup is a conductive device designed to catch or collect charged particles, such as ions or electrons, in a vacuum environment. When a beam of charged particles strikes the cup, electrons flow through a connected circuit to neutralize the charge. The resulting electric current is directly proportional to the number of particles hitting the cup. Faraday cups are highly accurate and robust universal charge detectors, independent of the energy, mass, or chemical nature of the particles.
Faraday cups are typically shielded from radiation produced, and can be either cooled (e.g., air or water) or uncooled. Even when deposited power is low, Faraday cups typically do need to be cooled because of the limited thermal conductivity of the isolated cup electrode.
The basic collection design for an electron-beam Faraday cup consists of a copper rod with a tapered hole at the entrance to limit the escape of secondary electrons. The collector is surrounded by a stainless-steel vacuum chamber and copper bar, and is attached to a Conflat flange and isolated from ground by a ceramic break. Some fraction of radiation escapes the central region in the form of gamma radiation and neutrons and must be shielded against. Because lead is ineffective as a shield against neutrons, iron is predominantly used as an outer shielding layer.
Xelera Research LLC designs and builds shielded Faraday cups for a range of applications. We perform all necessary radiation calculations to ensure appropriate shielding is in place. With your specifications for energy, average beam current, and overall size limits of the device, we will work with you to develop a custom design to meet your needs. Contact us to learn more.
Example gamma dose rate calculation for a shielded Faraday cup design: