plasma-facing components are the armored surfaces of a 📝fusion machine — principally the first wall and the divertor — that directly face the plasma and absorb its heat and particle flux.
The term, often shortened to PFCs, is the umbrella over two components with sharply different jobs. The 📝first wall covers most of the chamber's interior and takes a broad, comparatively gentle load of radiation and neutral particles; the 📝divertor takes the narrow, ferociously concentrated exhaust stream that magnetic geometry steers onto its targets. What unites them is that they are the only engineered surfaces in direct contact with the boundary of a 📝plasma whose core burns at over 100 million degrees, and every design decision about them ripples both ways — into the plasma, as impurity contamination when their atoms are sputtered loose, and into the machine, as erosion, melting risk, and retained fuel.
A plasma-facing component must therefore satisfy an unusually hostile requirements list: high melting point, resistance to erosion and thermal shock, tolerance of neutron damage arriving from the 📝D-T reaction, minimal retention of 📝tritium, and weak radiative penalty when its atoms do reach the core. No material meets every demand; tungsten's dominance in modern designs reflects the least painful compromise rather than an ideal.