An important overall measure of physics performance is the «triple product» of the peak ion density, the plasma energy confinement time and the peak ion temperature. (scientificamerican.com)
Both the F1 and F2 regions possess high ion density and are strongly influenced by both solar activity and time of day. (britannica.com)
It's the increased ion density that the University of Maryland researchers aim to detect with their new method. (sciencedaily.com)