Grain orientation and surface nanostructure impact physical sputtering of tungsten by neon plasmas

• The (111) grains in W are more resilient to physical sputtering than the (100) grains under Ne plasma exposure. • He plasma exposure induced W ‘fuzzy’ surfaces reduce physical sputtering yields up to 5 times when bombarded by Ne. The erosion of the tungsten (W) first wall by the seeding impurity neon (Ne) is foreseen in ITER. Accurate physical sputtering yields are crucial in defining the operating window that is consistent with the operational budget of the ITER divertor/main wall. However, the influence of crystal orientation and surface nanostructure—due to helium plasma exposure, on the physical sputtering yield is poorly understood. Here, we explore such influence for W bombarded by fusion-relevant Ne plasmas experimentally. In the first set of experiments, polished polycrystalline W targets were exposed to ∼ 50 eV Ne plasmas to a fluence of ∼ 3◊10 26 m −2 . Subsequent secondary electron imaging revealed pronounced selective surface erosion. Combined with electron backscatter diffraction, we found that the (111) grains were more resilient to physical sputtering than the (100) grains. In the second set of experiments, He plasma exposure was performed to generate ‘fuzzy’ surfaces prior to Ne plasma exposure. By monitoring the intensity ratio between the W I and Ne II emission lines, strongly reduced, nonlinear erosion of the ‘fuzzy’ surfaces was observed. Measurable physical sputtering yields as low as 20 % of the smooth counterpart were recorded, which decreased with increasing ‘fuzzy’ layer thickness. The results highlight the impact of grain orientation and surface nanostructure on the physical sputtering yield of W bombarded by Ne. Moreover, the sputtering resistance of the ‘fuzzy’ layer may be exploited to boost the first wall performance in fusion devices.