Surface-mediated reduction of radiation damage in tungsten revealed by advanced ion channeling analysis

Abstract

Tungsten is a leading candidate material for plasma-facing components in future fusion reactors. Extensive studies have been performed to better understand its behavior under irradiation. Recent experiments of Rutherford backscattering spectrometry in channeling mode indicated a marked reduction in radiation damage in single-crystal tungsten samples irradiated by self-ions when the irradiation temperature was increased from room temperature to 800 K. However, the underlying mechanism for this damage reduction remains unclear. In this work, by combining Rutherford backscattering spectrometry in channeling mode and molecular dynamics simulations, we identify a pronounced surface effect at elevated temperatures, characterized by a significant reduction of dislocation density near the surface. We demonstrate how our unique analysis method can clearly resolve a dislocation-free zone and a transition region with suppressed defect density before reaching the bulk value. The strong surface effect at elevated temperatures is explained by considering the coherent drift motion of dislocation loops towards the surface, highlighting alternative perspectives on mitigating radiation damage by increasing dislocation mobility.

Figures (4)

• Figure 1: Analysis of RBS/c signals and radiation damage in tungsten using the BCA-MD approach: (a) Experimental (symbols) and simulated (lines) RBS/c spectra of 3 MeV He ions on <111>-oriented tungsten samples at RT and 800 K (maximum damage dose: 0.02 dpa), and (b) depth distribution of dislocation density in the simulated targets.
• Figure 2: Analysis of RBS/c signals and radiation damage in tungsten using the Fit-MD approach: (a) Experimental (symbols) and simulated (lines) RBS/c spectra of 3 MeV He ions on <111>-oriented tungsten samples at RT and 800 K (maximum damage dose: 0.02 dpa), and (b) depth distribution of dislocation density in the simulated targets.
• Figure 3: Comparison of dislocation densities obtained from the BCA-MD and Fit-MD approaches at (a) RT and (b) 800 K.
• Figure 4: Evaluation of surface effects on 1/2<111> dislocation loops in tungsten: (a) Surface stress due to the vicinity of the open surface on the dislocation loop, and (b) time required for a dislocation loop to cross the dislocation-free zone (83 nm) as a function of temperature with different effective migration energies.