Editing Plasma diagnostics (section)

==Passive spectroscopy==
Passive [[spectroscopic]] methods simply observe the radiation emitted by the plasma. They can be collected by diagnostics such as the filterscope, which is used in various [[tokamak]] devices.<ref>{{Cite journal |last1=Colchin |first1=R. J. |last2=Hillis |first2=D. L. |last3=Maingi |first3=R. |last4=Klepper |first4=C. C. |last5=Brooks |first5=N. H. |date=2003 |title=The Filterscope |url=https://doi.org/10.1063/1.1537038 |journal=Review of Scientific Instruments |volume=74 |issue=3 |pages=2068–2070 |doi=10.1063/1.1537038 |bibcode=2003RScI...74.2068C |issn=0034-6748|url-access=subscription }}</ref>

===Doppler shift===
If the plasma (or one ionic component of the plasma) is flowing in the direction of the line of sight to the observer, emission lines will be seen at a different frequency due to the [[Doppler effect]].

===Doppler broadening===
The thermal motion of ions will result in a shift of emission lines up or down, depending on whether the ion is moving toward or away from the observer. The magnitude of the shift is proportional to the velocity along the line of sight. The net effect is a characteristic broadening of spectral lines, known as [[Doppler broadening]], from which the ion temperature can be determined.<ref>{{cite journal |last1=Gradic  |first1=D. |last2=Ford |first2=O.P. |display-authors=1|title=Doppler coherence imaging of divertor and SOL flows in ASDEX upgrade and Wendelstein 7-X |journal=Plasma Physics and Controlled Fusion |date=2018 |volume=60 |issue=8|pages=084007|doi=10.1088/1361-6587/aac4d2 |bibcode=2018PPCF...60h4007G |s2cid=125817653 |doi-access=free }}</ref>

===Stark effect===
The splitting of some emission lines due to the [[Stark effect]] can be used to determine the local electric field.

===Stark broadening===
Irrespectively of the presence of macroscopic electric fields, any single atom is affected by microscopic electric fields due to the neighboring charged plasma particles. This results in the [[Stark broadening]] of spectral lines that can be used to determine the plasma density.<ref>{{Cite book| publisher = Academic Press| last = Griem| first = Hans R.| title = Spectral line broadening by plasmas| location = New York| date = 1974}}</ref>

===Spectral line ratios===
{{main|Spectral line ratios}}
The brightness of [[atomic spectral line|spectral lines]] emitted by atoms in a plasma depends on the plasma temperature and density.

If a sufficiently complete [[collisional radiative model]] is used, the temperature (and, to a lesser degree, density) of plasmas can often be inferred by taking ratios of the emission intensities of various atomic spectral lines.<ref>{{Cite book| publisher = Cambridge University Press| isbn = 978-0-521-61941-7| last = Griem| first = Hans R.| title = Principles of Plasma Spectroscopy| location = Cambridge| series = Cambridge Monographs on Plasma Physics| date = 1997| url = https://www.cambridge.org/core/books/principles-of-plasma-spectroscopy/90F6DBB512089B7E3AC121744EFE3D93}}</ref><ref>{{Cite book| publisher = Springer Berlin Heidelberg| isbn = 978-3-642-02232-6| volume = 56| last = Kunze| first = Hans-Joachim| title = Introduction to Plasma Spectroscopy| location = Berlin, Heidelberg| series = Springer Series on Atomic, Optical, and Plasma Physics| date = 2009| doi = 10.1007/978-3-642-02233-3| bibcode = 2009ips..book.....K| url = http://link.springer.com/10.1007/978-3-642-02233-3}}</ref>

===Zeeman effect===
The presence of a magnetic field splits the atomic energy levels due to the [[Zeeman effect]]. This leads to broadening or splitting of spectral lines. Analyzing these lines can, therefore, yield the magnetic field strength in the plasma.