Editing Plasma diagnostics (section)

===Charge exchange recombination spectroscopy===
In extremely high-temperature plasmas, such as those found in magnetic fusion experiments, light elements become fully ionized and do not emit line radiation. However, when a beam of neutral atoms is fired into the plasma, a process known as [[charge exchange]] occurs. During charge exchange, electrons from the neutral beam atoms are transferred to the highly energetic plasma ions, leading to the formation of hydrogenic ions. These newly formed ions promptly emit line radiation, which is subsequently analyzed to obtain information about the plasma, including ion density, temperature, and velocity.

One example of this is the Fast-Ion Deuterium-Alpha (FIDA) method employed in tokamaks.<ref>{{Cite journal |last1=Heidbrink |first1=W. W. |last2=Luo |first2=Y. |last3=Muscatello |first3=C. M. |last4=Zhu |first4=Y. |last5=Burrell |first5=K. H. |date=2008 |title=A new fast-ion Dα diagnostic for DIII-D |url=https://pubs.aip.org/rsi/article/79/10/10E520/1070883/A-new-fast-ion-D-diagnostic-for-DIII-Da |journal=Review of Scientific Instruments |language=en |volume=79 |issue=10 |pages=10E520 |doi=10.1063/1.2956828 |pmid=19044502 |issn=0034-6748|url-access=subscription }}</ref><ref>{{Cite journal |last1=Jansen van Vuuren |first1=A. |last2=Geiger |first2=B. |last3=Jacobsen |first3=A. S. |last4=Cavedon |first4=M. |last5=Dux |first5=R. |last6=Köhnlein |first6=H. |last7=ASDEX Upgrade Team |date=2019 |title=An edge fast-ion D-alpha system installed at ASDEX Upgrade |url=https://pubs.aip.org/rsi/article/90/10/103501/360770/An-edge-fast-ion-D-alpha-system-installed-at-ASDEX |journal=Review of Scientific Instruments |language=en |volume=90 |issue=10 |doi=10.1063/1.5121588 |bibcode=2019RScI...90j3501J |issn=0034-6748|hdl=21.11116/0000-0004-CCFD-A |s2cid=209844219 |hdl-access=free }}</ref> In this technique, charge exchange occurs between the neutral beam atoms and the fast [[deuterium]] ions present in the plasma. This method exploits the substantial Doppler shift exhibited by [[Balmer series|Balmer-alpha]] light emitted by the energetic atoms in order to determine the density of the fast ions.<ref>{{Cite journal |last=Heidbrink |first=W. W. |date=2010 |title=Fast-ion Dα measurements of the fast-ion distribution (invited) |url=https://doi.org/10.1063/1.3478739 |journal=Review of Scientific Instruments |volume=81 |issue=10 |pages=10D727 |doi=10.1063/1.3478739 |pmid=21033920 |bibcode=2010RScI...81jD727H |issn=0034-6748}}</ref>