Editing CERN Axion Solar Telescope (section)

==Theory and operation==
If the [[axion]]s exist, they may be produced in the Sun's core when [[X-ray]]s scatter off electrons and protons in the presence of strong [[electric field]]s. The experimental setup is built around a 9.26&nbsp;m long decommissioned test magnet for the [[Large Hadron Collider|LHC]] capable of producing a field of up to {{val|9.5|ul=T}}. This strong [[magnetic field]] is expected to convert solar axions back into X-rays for subsequent detection by X-ray detectors. The telescope observes the Sun for about 1.5&nbsp;hours at sunrise and another 1.5&nbsp;hours at sunset each day. The remaining 21&nbsp;hours, with the instrument pointing away from the Sun, are spent measuring background axion levels.
[[File:Castexp1.jpg|thumb|442x442px|Members of the CAST Collaboration, 2011]]
CAST began operation in 2003 searching for axions up to {{val|0.02|ul=eV}}. In 2005, Helium-4 was added to the magnet, extending sensitivity to masses up to 0.39&nbsp;eV, then Helium-3 was used during 2008–2011 for masses up to 1.15&nbsp;eV. CAST then ran with vacuum again searching for axions below 0.02&nbsp;eV.

As of 2014, CAST has not turned up definitive evidence for solar axions. It has considerably narrowed down the range of parameters where these elusive particles may exist. CAST has set significant limits on axion coupling to electrons<ref name=cast2013/> and photons.<ref name=cast2011/>

A 2017 paper using data from the 2013–2015 run reported a new best limit on axion-photon coupling of 0.66×10{{sup|&minus;10}}&nbsp;''/''&nbsp;GeV.<ref name=":5">{{cite journal |last1=Anastassopoulos |first1=V. |display-authors=etal |collaboration=CAST Collaboration |date=2017 |title=New CAST limit on the axion-photon interaction |journal=[[Nature Physics]] |volume=13 |issue=6 |pages=584–590 |doi=10.1038/nphys4109 |doi-access=free |bibcode=2017NatPh..13..584A |arxiv=1705.02290}}</ref><ref>{{cite news |url=https://arstechnica.com/science/2017/05/axion-search-at-cern-sets-limits-on-these-possible-particles/ |title=CERN points giant magnet at the Sun to look for dark matter particles |work=Ars Technica |access-date=2017-05-02 |df=dmy-all |language=en-us}}</ref>

Built upon the experience of CAST, a much larger, new-generation, axion helioscope, the [[International Axion Observatory]] (IAXO), has been proposed and is now under preparation.<ref>{{cite journal |last1=Armengaud |first1=E. |display-authors=etal |collaboration=IAXO Collaboration |date=2014 |title= Conceptual Design of the International Axion Observatory (IAXO) |journal=[[JINST]] |volume=9 |issue=5 |page=T05002 |doi=10.1088/1748-0221/9/05/T05002 |bibcode=2014JInst...9.5002A |arxiv=1401.3233|s2cid=49209307 }}</ref>