Faraday cup (or cylinder) collector

https://dx.doi.org/10.1351/goldbook.F02326
A hollow collector, open at one end and closed at the other, used to collect beams of ions.
Source:
PAC, 1991, 63, 1541 (Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)) on page 1553