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

I used to study this at uni (nuclear engineer here) but i’m a bit rusty.

Consider that talking about temperature in plasma is a bit more nuanced than “normal” day-to-day temperature.

Hot means: it makes my atoms vibrate faster.
What happens if my atoms vibrate so fast that they get flung into space? Is it still hot or something different?

In general, temperature is linked to kinetic energy of the particles by a linear relation (temperature = energy * adjustment variable). But in gas, liquid and solid, you have fairly big (atoms, molecules) particles moving at a slow pace compared to their size.
So if you touch it, you interact basically by conduction, and feel the heat, thus a concept of temperature.

On a plasma for nuclear fusion, you have free electrons and protons (many time smaller than atoms) zooming by, close to the speed of light.
Getting close by, you will never get to “touch” them, they emit very high intensity beams of light that are strong enough to damage materials but so “tiny” that your temperature sensor (e.g. the nerves) might not be able to perceive it.
If you try and “touch” the plasma (don’t do it, it is very unhealthy to do so) it would move so fast and be so tiny that most of it would pass through you as if you were not there.

So the temperature you read is more a description of the speed of the electrons and protons running in circle at crazy speed, than a sensorial experience.
Infact scientists don’t measure it in celsius or kelvin, but in eV (electron volts) that is a measure of energy.
1eV = 10’000 C more or less.

Of course this mad running releases energy in form of invisible (x-rays gamma-rays) light that hit the metal casing and cooling fluid, heating them up.

I suggest that you should cosider the plasma “fast” rather than “hot”.