How can we contain something that gets as hot as 100M Celsius? And how can we measure it?

Question

I have been reading articles describing the progress made towards fusion energy and got intrigued by how they do it.
https://www.msn.com/en-us/money/other/nuclear-fusion-reactor-sustains-plasma-at-100-million-c-for-30-seconds/ar-AA11BpC8

In: 71

Answer 1

It is levitated with magnets in a vacuum chamber with essentially no air and thick shielding around it with a lot of cooling loops.

You can measure the temperature by the radiation it emits. Kinda like how a blue flame is hotter than an orange one.