Editing Advanced Composition Explorer (section)

=== Solar Wind Ion Composition Spectrometer (SWICS) and Solar Wind Ion Mass Spectrometer (SWIMS) ===
[[File:ACE-swics sm.jpg|thumb|SWICS]]
[[File:ACE-swims sm.jpg|thumb|SWIMS]]
The Solar Wind Ion Composition Spectrometer (SWICS) and the Solar Wind Ions Mass Spectrometer (SWIMS) on ACE are instruments optimized for measurements of the chemical and isotopic composition of solar and interstellar matter. SWICS determined uniquely the chemical and ionic-charge composition of the [[solar wind]], the thermal and mean speeds of all major solar wind ions from H through Fe at all solar wind speeds above 300&nbsp;km/s<sup>−1</sup> (protons) and 170&nbsp;km/s<sup>−1</sup> (Fe+16), and resolved H and He isotopes of both solar and interstellar sources. SWICS also measured the distribution functions of both the interstellar cloud and dust cloud [[pickup ion]]s up to energies of 100 keV/e<sup>−1</sup>. SWIMS measures the chemical, isotopic and charge state composition of the solar wind for every element between He and Ni. Each of the two instruments are time-of-flight [[mass spectrometer]]s and use electrostatic analysis followed by the time-of-flight and, as required, an energy measurement.<ref name=gloeckler98>{{cite journal |last=Gloeckler |first=G. |title=Investigation of the composition of solar and interstellar matter using solar wind and pickup ion measurements with SWICS and SWIMS on the ACE spacecraft |journal=Space Science Reviews |date=July 1998 |volume=86 |pages=497–539 |doi=10.1023/A:1005036131689 |bibcode=1998SSRv...86..497G |s2cid=189787814|display-authors=et al.}}</ref><ref>{{cite web |url=http://solar-heliospheric.engin.umich.edu/ace/ |title=ACE/SWICS and ACE/SWIMS |publisher=The Solar and Heliospheric Research Group |access-date=June 30, 2006 |archive-url=https://web.archive.org/web/20060810115838/http://solar-heliospheric.engin.umich.edu/ace/ |archive-date=August 10, 2006 |url-status=live}}</ref>

On 23 August 2011, the SWICS time-of-flight electronics experienced an age- and radiation-induced hardware anomaly that increased the level of background in the composition data. To mitigate the effects of this background, the model for identifying ions in the data was adjusted to take advantage of only the ion energy-per-charge as measured by the electrostatic analyzer, and the ion energy as measured by solid-state detectors. This has allowed SWICS to continue to deliver a subset of the data products that were provided to the public prior to the hardware anomaly, including ion charge state ratios of oxygen and carbon, and measurements of solar wind iron. The measurements of proton density, speed, and thermal speed by SWICS were not affected by this anomaly and continue to the present day.<ref name="ACE Home Page"/>