Advancements in understanding helium retention behavior in plasma facing component for fusion reactor applications

Researchers have employed a combination of thermal desorption spectroscopy (TDS), neutron depth profiling (NDP), and laser ablation mass spectrometry (LAMS) alongside cluster dynamics modeling to investigate helium retention and migration in tungsten. These findings are critical for understanding the performance of tungsten in fusion reactor environments and predicting the evolution of helium-induced microstructural changes.

Introduction to Tungsten-based Plasma Facing Components in Fusion Reactors

Tungsten is a leading candidate for plasma-facing components in fusion reactors due to its high melting point, excellent thermal conductivity, and low tritium retention. However, exposure to high-energy neutrons and low-energy helium particles can induce significant microstructural changes, affecting its thermal and mechanical properties. Understanding helium behavior in tungsten is essential for predicting its long-term performance in fusion environment.

Experimental Methods and Material Preparation

Researchers prepared ultra-high-purity tungsten samples and subjected them to helium ion implantation at various fluences. The experimental techniques employed included:

• Thermal Desorption Spectroscopy (TDS): Measured helium release during thermal annealing.
• Neutron Depth Profiling (NDP): Nondestructively quantified helium depth distribution using the large thermal neutron absorption cross-section of ³He.
• Laser Ablation Mass Spectrometry (LAMS): Provided additional data on helium depth profiles by analyzing ablated material.

Key Experimental Findings (Figure 2 and Figure 3)

1. Helium Desorption Spectra:
   • TDS measurements revealed distinct desorption peaks at 200°C, 250°C, and 1000°C, indicating different trapping sites for helium in tungsten.
   • Higher implantation fluences resulted in increased helium desorption flux, with notable peaks at 620°C and 320°C for the highest and medium fluence samples, respectively.
2. Helium Depth Profiling:
   • NDP and LAMS results showed that helium concentrations peaked near the surface (30–50 nm) and extended to depths exceeding 200 nm after annealing.
   • NDP data exhibited broader profiles due to detector resolution and sample morphology, while LAMS provided more localized depth information.
3. Cluster Dynamics Modeling:
   • A cluster dynamics model based on diffusion-reaction rate theory successfully predicted helium spatial distribution and desorption spectra.
   • Optimization of binding energies for small helium-vacancy clusters improved model accuracy, aligning closely with experimental results.

Implications for Fusion Reactor Design

The study highlights the importance of helium-vacancy cluster interactions in determining tungsten's performance under irradiation. Key insights include:

• Helium retention is strongly influenced by defect cluster evolution and thermal stability.
• Surface desorption is the primary mechanism for helium loss, with limited diffusion into bulk material.
• The model provides a predictive framework for helium bubble nucleation and growth, critical for designing tungsten components in next-generation fusion reactors.

Conclusion 

This work is led by Dr. Jie Qiu and Dr. Congyi Li at Shanghai Jiao Tong University. The comprehensive investigation combining experimental characterization and computational modeling advances the understanding of helium behavior in tungsten. The validated cluster dynamics model offers a robust tool for predicting tungsten's response to helium implantation and thermal annealing, supporting the development of high-performance plasma-facing materials for fusion energy applications.

The complete study is accessible via DOI: 10.1007/s41365-025-01637-z

Nuclear Science and Techniques (NST) is a peer-reviewed international journal sponsored by the Shanghai Institute of Applied Physics, Chinese Academy of Sciences. The journal publishes high-quality research across a broad range of nuclear science disciplines, including nuclear physics, nuclear energy, accelerator physics, and nuclear electronics. Its Editor-in-Chief is the renowned physicist, Professor Yu-Gang Ma.