An ion trap is a combination of electric or magnetic fields that captures ions in a region of a vacuum system or tube. Ion traps have a number of scientific uses such as mass spectrometery and trapping ions while the ion's quantum state is manipulated. The two most common types of ion traps are the Penning trap and the Paul trap (quadrupole ion trap).
When using ion traps for scientific studies of quantum state manipulation, the Paul trap is most often used. This work may lead to a trapped ion quantum computer and has already been used to create the world's most accurate atomic clocks.
An ion trap mass spectrometer may incorporate a Penning trap (Fourier transform ion cyclotron resonance), Paul trap or the Kingdon trap. The Orbitrap, introduced in 2005, is based on the Kingdon trap. Other types of mass spectrometers may also use a linear quadrupole ion trap as a selective mass filter.
In an electron gun (a device emitting high-speed electrons, such as those in CRTs), an ion trap may be implemented above the cathode (using an extra, positively-charged electrode between the cathode and the extraction electrode) to prevent its degradation by positive ions accelerated backward by the fields intended to pull electrons away from the cathode.
 Penning ion trap
 Paul ion trap
 Kingdon trap
A Kingdon trap consists of a thin central wire and an outer cylindrical electrode. A static applied voltage results in a radial logarithmic potential between the electrodes.
 Cathode ray tubes
Devices known as ion traps were used in early television receivers, prior to the introduction of aluminized CRT faces in approximately 1958. The ion trap must be delicately adjusted for maximum brightness. The purpose of these devices was to prevent ions from discoloring the phosphor screen.
 See also
- R. Blatt and D. J. Wineland (2008). "Entangled states of trapped atomic ions". Nature 453 (7198): 1008–1014. Bibcode:2008Natur.453.1008B. doi:10.1038/nature07125. PMID 18563151.
- T. Rosenband, D. B. Hume, P. O. Schmidt, C. W. Chou, A. Brusch, L. Lorini, W. H. Oskay, R. E. Drullinger, T. M. Fortier, J. E. Stalnaker, S. A. Diddams, W. C. Swann, N. R. Newbury, W. M. Itano, D. J. Wineland, and J. C. Bergquist (2008). "Frequency Ratio of Al+ and Hg+ Single-Ion Optical Clocks; Metrology at the 17th Decimal Place". Science 319 (5871): 1808–1812. Bibcode:2008Sci...319.1808R. doi:10.1126/science.1154622. PMID 18323415.
- Blaum, Klaus (2006). "High-accuracy mass spectrometry with stored ions". Physics Reports 425 (1): 1–78. Bibcode:2006PhR...425....1B. doi:10.1016/j.physrep.2005.10.011.
- Douglas, D.J.; Frank, AJ; Mao, DM (2005). "Linear ion traps in mass spectrometry". Mass Spectrometry Reviews 24 (1): 1–29. doi:10.1002/mas.20004. PMID 15389865.
- Kingdon KH (1923). "A Method for the Neutralization of Electron Space Charge by Positive Ionization at Very Low Gas Pressures". Physical Review 21 (4): 408–418. Bibcode:1923PhRv...21..408K. doi:10.1103/PhysRev.21.408.
- Hu, QZ; Noll, RJ; Li, HY; Makarov, A; Hardman, M; Cooks, RG (2005). "The Orbitrap: a new mass spectrometer". Journal of Mass Spectrometry 40 (4): 430–443. doi:10.1002/jms.856. PMID 15838939.
- Kingdon KH (1923). "A Method for the Neutralization of Electron Space Charge by Positive Ionization at Very Low Gas Pressures" (subscription required). Physical Review 21 (4): 408. Bibcode:1923PhRv...21..408K. doi:10.1103/PhysRev.21.408.
- Magnet for cathode-ray tube ion traps
- Ion Trap for a Cathode Ray Tube
- Hartson, Ted (2004). "How the World Changed Television". Retrieved 2008-10-13.