Fusion reactor environments inevitably lead to the formation of high-pressure helium bubbles whose nucleation, growth, and diffusion strongly impact the performance of plasma-facing components. This research describes a diffusion mechanism of over-pressurized bubbles via a sequence of Frenkel pair nucleation, self-interstitial migration, and Frenkel pair annihilation. Molecular dynamics was used to simulate the diffusion of small bubbles in tungsten at 2000 K with helium-per-vacancy ratios in the range of 4.5 to 7. The diffusion coefficients are calculated and their dependence on helium content, number of vacancies, and number of attached self-interstitials is characterized. It is found that bubbles are most mobile when the nucleation/annihilation rates of Frenkel pairs are nearly equal and when the bubbles nucleate and annihilate a single self-interstitial. All bubbles experience a peak diffusivity, which can be as high as ${10}^{-11}$ m${}^2$/s decreasing with bubble size. The calculated diffusion coefficients provide valuable insight into the mobility of small, high-pressure bubbles, and can be used as input parameters in mesoscale models to improve predictions of plasma-surface interactions. (LA-UR-21-21881)

聚变反应堆环境不可避免地导致高压氦气泡的形成，其成核、生长和扩散会强烈影响面向等离子体的组件的性能。本研究通过一系列 Frenkel 对成核、自填隙迁移和 Frenkel 对湮灭描述了超压气泡的扩散机制。分子动力学用于模拟 2000 K 下小气泡在钨中的扩散，氦/空位比在 4.5 到 7 的范围内。计算扩散系数及其对氦含量、空位数量和空位数量的依赖性附着自填隙物的特点。发现当 Frenkel 对的成核/湮灭率几乎相等并且气泡成核和湮灭单个自填隙时，气泡最易移动。所有气泡都会经历一个峰值扩散率，可以高达${10}^{-11}$ 米${}^2$/s 随气泡大小而减小。计算出的扩散系数为了解高压小气泡的流动性提供了宝贵的见解，并可用作中尺度模型中的输入参数，以改进对等离子体表面相互作用的预测。(LA-UR-21-21881)