December 2020, ScientificAmerican.com 73TEMPERATURE GRADIENT: ITER will include one of the hottest places
in the universe—the vacuum vessel housing the 150-million-degree-
Celsius plasma—as well as one of the coldest places in the universe;
the magnets that will confine and control that plasma must be kept
at about four kelvins (–269 degrees C). Separating the two will be
a beryllium-coated steel “blanket” to shield the sections from each
other, which will attach to the vacuum vessel’s interior wall via stub
keys, currently covered by yellow caps to keep off dust.