Vacancy and Helium-Cluster Thermomigration in Tungsten
Abstract
Strong thermal gradients in tungsten plasma-facing components can bias the migration of irradiation-induced defects and thereby alter their redistribution, interaction, and retention. Here, we extend an atomistic jump-statistics framework previously developed for hydrogen to quantify the thermomigration of a single vacancy and interstitial He1--He4 clusters in body-centered-cubic tungsten. Non-equilibrium molecular-dynamics simulations performed over several thermal gradients are used to determine the directional jump ratio, while geometrically derived projected jump lengths convert the fitted directional-bias coefficient into the heat-of-transport coefficient Q*=αkT2, where k is the Boltzmann constant, T the temperature, and α a constant. All investigated defects exhibit negative values of α, corresponding to net migration toward the hot region. He4 has the largest response, α=−2.2457×10−2 K−1, followed closely by the vacancy, whereas He3 exhibits the weakest response despite its intermediate cluster size. Independent constant-temperature simulations over 1000--1600 K show that He3 is also the least mobile cluster and has the largest effective migration energy, Emeff=0.271 eV. In contrast, He4 is more mobile than He3 and has the smallest effective migration energy, 0.087 eV. Agreement between the He3 concentration profile predicted from the jump statistics and that obtained from a long molecular-dynamics trajectory provides an independent validation of the method. These results show that thermomigration cannot be inferred from cluster size, diffusivity, or migration energy alone and provide defect-specific heat-of-transport parameters for higher-length-scale models of tungsten under fusion-relevant thermal gradients.
Related
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BibTeX
@misc{alturk2026vacancy,
title = {{Vacancy and Helium-Cluster Thermomigration in Tungsten}},
author = {Sanad Alturk and Enrique Martinez},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.26667},
eprint = {2610.26667},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.26667},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Vacancy and Helium-Cluster Thermomigration in Tungsten
AU - Sanad Alturk
AU - Enrique Martinez
PY - 2026
DA - 2026/10/19
PB - arXiv
DO - 10.48550/arxiv.2610.26667
UR - https://arxiv.org/abs/2610.26667
AB - Strong thermal gradients in tungsten plasma-facing components can bias the migration of irradiation-induced defects and thereby alter their redistribution, interaction, and retention. Here, we extend an atomistic jump-statistics framework previously developed for hydrogen to quantify the thermomigration of a single vacancy and interstitial He_1--He_4 clusters in body-centered-cubic tungsten. Non-equilibrium molecular-dynamics simulations performed over several thermal gradients are used to determine the directional jump ratio, while geometrically derived projected jump lengths convert the fitted directional-bias coefficient into the heat-of-transport coefficient Q^*=αkT^2, where k is the Boltzmann constant, T the temperature, and α a constant. All investigated defects exhibit negative values of α, corresponding to net migration toward the hot region. He_4 has the largest response, α=−2.2457×10^−2 K^−1, followed closely by the vacancy, whereas He_3 exhibits the weakest response despite its intermediate cluster size. Independent constant-temperature simulations over 1000--1600 K show that He_3 is also the least mobile cluster and has the largest effective migration energy, E_m^eff=0.271 eV. In contrast, He_4 is more mobile than He_3 and has the smallest effective migration energy, 0.087 eV. Agreement between the He_3 concentration profile predicted from the jump statistics and that obtained from a long molecular-dynamics trajectory provides an independent validation of the method. These results show that thermomigration cannot be inferred from cluster size, diffusivity, or migration energy alone and provide defect-specific heat-of-transport parameters for higher-length-scale models of tungsten under fusion-relevant thermal gradients.
ER -