The Influence of Microstructure on Deuterium Retention in Polycrystalline Tungsten

Abstract

The retention of hydrogen isotopes in the plasma-facing materials of a fusion reactor is dependent on the density of trapping sites in the material. One factor that can influence the trapping defects is the surface state of the material before exposure. Mechanically polished, electropolished, and recrystallized tungsten samples were compared by exposing them to 350 eV D⁺ beams with peak fluences of ~1 × 10²⁴ D⁺/m² at 500 and 740 K at the Multicharged Ion Research Facility (MIRF). At the exposure temperature of 740 K, no significant retention was detected. For material exposed at 500 K, significant differences in retention were observed, and the order of increasing retention was recrystallized, electropolished, and mechanically polished. The other variable besides surface treatment was the time delay between ion exposure and thermal desorption spectroscopy which also may have impacted the retention measurements if there was out-gassing of the D while samples were in storage before thermal desorption spectroscopy (TDS).

Keywords:

• Deuterium retention
• plasma-facing materials
• surface preparation
• recrystallized

Acknowledgments

This research was supported by the Oak Ridge National Laboratory (ORNL) LDRD program. ORNL is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the U.S. Department of Energy. The authors would like to thank Y. Katoh and C. Parish for helpful discussions on the manuscript.