Helium Bubble Coalescence in Plasma-Facing Tungsten.

Area of Science:

• Materials Science
• Computational Physics
• Nuclear Engineering

Background:

• Plasma-facing components (PFCs) in fusion reactors experience significant helium implantation.
• Helium bubble formation and coalescence impact material integrity and performance.
• Understanding helium behavior in tungsten is critical for reactor longevity.

Purpose of the Study:

• To systematically study helium bubble coalescence in tungsten under fusion reactor conditions.
• To investigate the thermodynamics and kinetics governing bubble interactions.
• To identify key mechanisms driving coalescence.

Main Methods:

• Computational study using molecular statics and molecular dynamics simulations.
• Examination of a multidimensional parameter space (size, separation, pressure, growth rate).
• Analysis of interaction energetics and coalescence mechanisms.

Main Results:

• Bubble interaction described by a square-well potential with a pressure-dependent capture radius.
• Dumbbell configurations form at short separations; open channels form when the separating ligament is ~1 atom thick.
• Coalescence is accelerated by stress-driven channel formation, Frenkel-pair production, and dislocation emission.

Conclusions:

• Helium bubble coalescence in tungsten is a complex process influenced by bubble pressure and inter-bubble distance.
• Defect formation and dislocation dynamics play crucial roles in facilitating coalescence.
• Findings provide insights into helium retention and material degradation in fusion environments.