Plasma Diagnostics Overview
You cannot put a thermometer in a 100-million-degree plasma; you measure it with light, waves and particles instead.
A fusion plasma is far too hot for any probe to touch, so its temperature, density, current and impurity content are inferred remotely — from the light it emits, the way it bends waves passed through it, and the particles and neutrons that escape. A modern machine carries dozens of such diagnostics, and Kronos's control and validation both lean on them.
Common questions
They measure the plasma — temperature, density, position, radiation, neutrons — both to control it in real time and to demonstrate performance against the design targets.
Magnetic sensors for fast position and shape control, since the control loop can only hold the plasma as well as it can see it.