Influence of dual beam ion irradiation and transient heat loading on tungsten surface morphology and erosion.

Abstract Material testing for plasma facing components (PFCs) in future fusion devices reveals important damage mechanisms that impact lifetime and performance. During operation, PFCs in the divertor region will be subjected to high particle fluxes and heat loads. Tungsten (W) is currently the leading candidate material for divertor PFCs, due to its high melting point, high thermal conductivity, and low tritium retention. Laboratory experiments have effectively characterized mechanisms of damage on W due to different forms of radiation. However, understanding how different species of incident plasma particles interact with one another to affect the resultant strength of the material remains in development. In this study, W samples were exposed to simultaneous ELM-like heat loading and high-flux He+ and D+ ion irradiation at different ELM intensities to further elucidate the complex synergistic effects inherent in a fusion environment. ELM-like heat loading was replicated using a 1064 nm Nd:YAG pulsed millisecond laser at different energy densities. Exposures produced a shale-like microstructure with or without concurrent He+ and D+ ion irradiation. However, adding D+ to a simultaneous laser + He+ irradiation reduced pore formation and inhibited early-stage nanostructure formation. Changes in surface morphology with the addition of D+ could be attributed to super-saturation in the near-surface layer. While the addition of He+ and D+ clearly increased W erosion, the laser energy density did not have as clear of an effect. Increasing the ELM intensity reduced the number of pores, but increased the pore size. Future studies need to explore whether near-surface D impacts pore formation and total He desorption. Continued research on the combined effect of high-flux particle irradiation and transient heat loading will help refine predictions of material performance for ITER and beyond. [ABSTRACT FROM AUTHOR]