Plasma-Facing-Component Thermal Monitoring
The wall and divertor tiles take intense heat while the plasma runs, so their temperatures are watched continuously to catch overloads before damage.
What is watched
Plasma-facing components, first-wall panels, limiters, and divertor targets, absorb radiated and conducted power from the plasma. Their surface and structure temperatures must stay below limits set by melting, sublimation, thermal stress, and coolant conditions. Monitoring these temperatures in real time is both a control input and a protection function.
Sensors
Infrared cameras image the surface temperature across wide areas and reveal hot spots and their movement. Embedded thermocouples give slower but robust local readings and coolant inlet-outlet temperatures give the integrated heat load. Together they cover fast surface transients and steady bulk heating. Calibrating infrared readings requires knowing the surface emissivity, which changes as the surface erodes and deposits.
Real-time protection
A monitoring system flags any component exceeding its temperature limit and, on a hard threshold, commands mitigation: reduce heating power, increase impurity seeding to spread the load, or terminate the pulse. Because a hot spot can grow quickly, the fast infrared channels feed a protection layer with a short reaction time, independent of slower analysis.
- Surface and structure temperatures must stay in limits
- IR cameras catch fast hot spots; thermocouples give bulk load
- Emissivity drift complicates IR calibration
- Over-temperature triggers mitigation or termination
Kronos context
In the Hyperion breeder design study, plasma-facing components must handle the exhaust of a high-power spherical tokamak, and their thermal margins constrain heating and divertor control. In the burner, D-3He operation gives a lower neutron fraction, about 5.44 percent, which changes the wall loading balance toward charged-particle and radiation heat. Both machines are simulation and design cases; the monitoring here is described as a general subsystem behaviour.
Thermal monitoring is the sense of touch that keeps the plasma from harming its own container.