Figure 1
From: Engineering self-organising helium bubble lattices in tungsten

Schematic showing: (a) Diffusion of a <111> crowdion in the close-packed <111> direction in the BCC structure as described by the 1-D SIA model; (b) diffusion of a <110> dumbbell in the (110) plane as described by the 2-D SIA diffusion model; and (c) forbidden rotation of a <110> dumbbell onto the (011) plane which would give rise to 3-D SIA diffusion.