He wall bombardment and wall erosion in fusion devices

Abstract

A small fraction of the α-particles produced in a future (D, T)-fusion plasma will escape directly and hit some areas of the surrounding solid walls with their full energy, while the majority will be confined in the magnetic field, slowed down in the plasma and reach the first wall with about the same energy distribution as the other plasma particles.

During bombardment of a solid by energetic α-particles the implanted surface layers undergo several modifications leading finally to a rough surface with a spongy microstructure. Some of these modifications, i.e. blistering and flaking, are only observed if the critical gas concentration builds up first at some depth below the surface. This condition is met only if simultaneous erosion by sputtering stays below a certain limit. In fusion devices with loss fractions of ≲ 1% high energy α-particles and a plasma temperature near the first wall above some 10 eV, blistering and flaking are likely to be avoided.