New Insight into the Quantifying Vacancy Distribution in Self-Ion-Irradiated Tungsten: A Combined Experimental and...

Area of Science:

• Materials Science
• Nuclear Engineering
• Condensed Matter Physics

Background:

• Tungsten is crucial for fusion energy applications.
• Understanding radiation-induced defects in tungsten is vital for reactor longevity.
• Previous methods struggled to detect small, low-concentration defects.

Purpose of the Study:

• To develop and validate a novel positron annihilation spectroscopy (PAS) approach.
• To accurately quantify vacancy-type defect concentrations in self-ion irradiated tungsten.
• To identify and characterize defect clusters not observable by conventional techniques like transmission electron microscopy (TEM).

Main Methods:

• Utilized positron annihilation spectroscopy (PAS) for defect analysis.
• Employed quadratic programming and simulated annealing for data extraction.
• Integrated a positron trapping model with two-component density functional theory (2c-DFT) calculations for annihilation characteristics.
• Validated findings against simulation data and transmission electron microscopy (TEM).

Main Results:

• Successfully estimated vacancy-type defect concentrations in tungsten irradiated at various temperatures.
• Unveiled small, TEM-undetectable vacancy clusters formed during high-temperature irradiation.
• Observed concentrations of these small clusters significantly exceeding TEM-visible defects (up to 10^24 m^-3).
• Demonstrated that including positron trapping in oxygen-vacancy complexes accurately models high-temperature irradiation data.

Conclusions:

• The developed PAS method offers enhanced sensitivity for defect characterization in irradiated materials.
• High-temperature irradiation produces significant concentrations of small, previously hidden vacancy clusters.
• Accurate defect modeling requires consideration of complexes like oxygen-vacancy interactions.