The response of polycrystalline tungsten to 30 keV helium ion implantation at normal incidence and high temperatures

Polycrystalline tungsten samples were irradiated with 30 keV helium ions in the Materials Irradiation Experiment (MITE-E). Samples were held at temperatures of 500-900 degrees C while irradiated to fluences of similar to 6 x 10(16) to similar to 4 x 10(19) He/cm(2). Drastic changes to the surface morphology were observed at implant doses exceeding similar to 1 x 10(18) He/cm(2) and classified as blisters, pitting, or a highly directional surface structure dubbed "grass." Morphological details of the grass structure depended on the crystal orientation of the grains at the sample surface. A sub-surface semi-porous layer was formed during irradiation. Post-implantation analysis revealed that this layer extended up to similar to 1000 nm below the surface in the highest fluence cases. Specimens irradiated to fluences in excess of similar to 1 x 10(18) He/cm(2) experienced statistically significant mass loss which increased with higher implant dose. Implications of this mass loss are discussed for the plasma facing components of both magnetic and inertial fusion reactors. (c) 2011 Elsevier B.V. All rights reserved.