Laser repair of tungsten damaged by fusion-relevant plasmas

As a hotspot, the ITER tungsten divertor receives both extreme plasmas and considerable research attention. The projection is that certain plasma-induced defects in tungsten are inevitable under the scheduled ITER operation. Although the exact consequences of such defects on the divertor lifetime are unclear currently, approaches to combat them are desirable but remain limited. Here, we develop the idea of healing such defects through laser remelting. With a suitable combination of processing parameters—such as laser power, scan speed, and preheating temperature—the remelted (pristine) tungsten surface was nearly crack-free. Revealed by electron backscatter diffraction (EBSD) analysis, the remelted microstructure resembled that of fully recrystallized tungsten. Furthermore, the linear relationship between the normalized melt pool depth and the normalized enthalpy of the surface was established, the former of which indicates the healing depth. Lastly, proof-of-principle experiments were performed on damaged tungsten specimens containing respectively blisters, nanostructure fuzz, and fatigue cracks, yielding promising healing effects. Based on additional considerations of the plasma exposure behavior of laser remelted tungsten and deployment of the laser repair system, we conclude that the laser repair approach is compatible with the ITER operation plan.