Image of ionized deuterium in an IEC reactor. Image shows with high clarity the characteristic pinkish-red glow of ionized deuterium. By bencbartlett, [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia

https://en.wikipedia.org/wiki/File:Deuterium_Ionized.JPG