Infrared Thermography for Plasma-Facing Components
Infrared cameras turn the glow of hot surfaces into real-time temperature maps that reveal heat-flux patterns and hot spots on the wall.
How it works
Every surface emits thermal radiation whose intensity and spectrum depend on its temperature. An infrared camera measures this radiation and, given the surface emissivity, converts it into a temperature map. Wide-angle views let a few cameras cover large areas of the divertor and first wall, imaging where the plasma deposits power.
From temperature to heat flux
The surface temperature history can be inverted, through a heat-conduction model of the tile, to estimate the incident heat flux. This is more useful for control than temperature alone because it directly shows the load the plasma is imposing. The inversion needs the tile's material properties and thickness and assumes the tile is intact, so surface layers and cracks complicate it.
Calibration challenges
Emissivity is the weak link: it depends on the surface finish, which changes as the wall erodes, deposits material, and grows layers during operation. Cameras must be recalibrated, and control logic uses conservative limits to allow for calibration drift. Reflections from other hot surfaces and windows that darken under neutron and particle exposure add further error.
- IR radiation maps surface temperature over wide areas
- Inversion yields incident heat flux for control
- Emissivity drift from erosion and deposits limits accuracy
- Window darkening and reflections add error
Use in control
Real-time thermography feeds hot-spot protection and divertor heat-flux control, guiding strike-point sweeping and impurity seeding to spread the load. It also supports post-pulse analysis of wall condition. In the Kronos breeder design study, thermography is one channel among several for protecting plasma-facing components of the modeled spherical tokamak; the machine is a simulation and design case, and these behaviours are described in general terms.
Thermography gives operators a live picture of where the plasma is pressing hardest on the wall.