Editing Plasma diagnostics (section)

===Energy analyzer===
An energy analyzer is a probe used to measure the energy distribution of the particles in a plasma. The charged particles are typically separated by their velocities from the electric and/or magnetic fields in the energy analyzer, and then discriminated by only allowing particles with the selected energy range to reach the detector.

Energy analyzers that use an electric field as the discriminator are also known as retarding field analyzers.<ref>{{Cite journal|last1=Pitts|first1=R. A.|last2=Chavan|first2=R.|last3=Davies|first3=S. J.|last4=Erents|first4=S. K.|last5=Kaveney|first5=G.|last6=Matthews|first6=G. F.|last7=Neill|first7=G.|last8=Vince|first8=J. E.|last9=Duran|first9=I.|date=2003|title=Retarding field energy analyzer for the JET plasma boundary|journal=Review of Scientific Instruments|volume=74|issue=11|pages=4644–4657|doi=10.1063/1.1619554|issn=0034-6748|bibcode=2003RScI...74.4644P|s2cid=31524396}}</ref><ref>{{Cite journal|last1=Stenzel|first1=R. L.|last2=Williams|first2=R.|last3=Agüero|first3=R.|last4=Kitazaki|first4=K.|last5=Ling|first5=A.|last6=McDonald|first6=T.|last7=Spitzer|first7=J.|date=1982|title=Novel directional ion energy analyzer|journal=Review of Scientific Instruments|volume=53|issue=7|pages=1027–1031|doi=10.1063/1.1137103|issn=0034-6748|bibcode=1982RScI...53.1027S}}</ref> It usually consists of a set of grids biased at different potentials to set up an electric field to repel particles lower than the desired amount of energy away from the detector. Analyzers with  cylindrical or conical face-field <ref>A. M. Ilyin (2003). "New class of electrostatic energy analyzers with a cylindrical face-field". Nuclear Instruments and Methods in Physics Research Section A. 500 (1–3): 62–67. Bibcode:2003NIMPA.500...62I. doi:10.1016/S0168-9002(03)00334-6.</ref> can be more effective in such measurements.

In contrast, energy analyzers that employ the use of a magnetic field as a discriminator are very similar to [[mass spectrometer]]s. Particles travel through a magnetic field in the probe and require a specific velocity in order to reach the detector. These were first developed in the 1960s,<ref>{{Cite journal|last1=Eubank|first1=H. P.|last2=Wilkerson|first2=T. D.|date=1963|title=Ion Energy Analyzer for Plasma Measurements|journal=Review of Scientific Instruments|volume=34|issue=1|pages=12–18|doi=10.1063/1.1718108|issn=0034-6748|bibcode=1963RScI...34...12E|doi-access=free}}</ref> and are typically built to measure ions. (The size of the device is on the order the particle's [[gyroradius]] because the discriminator intercepts the path of the gyrating particle.)

The energy of neutral particles can also be measured by an energy analyzer, but they first have to be ionized by an electron impact ionizer.