Faraday cup
metal (conductive) cup designed to catch charged particles in vacuum
A Faraday cup is a metal (conductive) cup designed to catch charged particles. The resulting current can be measured and used to determine the number of ions or electrons hitting the cup. The Faraday cup was named after Michael Faraday who first theorized ions around 1830.
Examples of devices which use Faraday cups include space probes (Voyager 1, & 2, Parker Solar Probe, etc.) and mass spectrometers. Faraday cups can also be used to measure charged aerosol particles.
Principle of operation
When a beam or packet of ions or electrons (e.g. from an electron beam) hits the metallic body of the cup, the apparatus gains a small net charge. The cup can then be discharged to measure a small current proportional to the charge carried by the impinging ions or electrons. By measuring the electric current (the number of electrons flowing through the circuit per second) in the cup, the number of charges can be determined. For a continuous beam of ions (assumed to be singly charged) or electrons, the total number N hitting the cup per unit time (in seconds) is
N
t
=
I
e
{\displaystyle {\frac {N}{t}}={\frac {I}{e}}}
where I is the measured current (in amperes) and e is the elementary charge (1.60 × 10−19 C).
“Faraday cup” enters the record as metal (conductive) cup designed to catch charged particles in vacuum. Crown Archives preserves that source wording while asking what Faraday, metal and conductive can confirm, complicate or overturn.
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Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated May 25, 2025. The linked authority identifier is Q19410. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1830.
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This entry incorporates text from “Faraday cup” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.