Possible approaches for simulating the formation of fuzz structure on tungsten surface under helium irradiation

In this paper, we used the conventional method to simulate the helium irradiation on tungsten (110) surface with irradiation energy of 30 eV at temperature of 1300 K. Traditional methods involve simulating the helium incident process in the simulation We found that the first peak of the atomic density depth distribution of tungsten can well divide tungsten into the fuzz region and the bulk region. The helium in tungsten is uniformly distributed in the fuzz region and follows a lognormal distribution in the bulk region, and these distributions are stable and almost do not change with time. Based on this, we propose an acceleration method for molecular dynamics simulation of helium irradiation induced fuzz formation. The idea of this method is to directly add a certain amount of helium with uniform distribution and lognormal distribution in the fuzz and bulk regions of tungsten, respectively. Then, execute temperature equilibration to achieve a stable structure of the system, and finally repeat this process. This acceleration method can obtain similar helium depth distribution and tungsten surface morphology as conventional methods, and the growth rate of fuzz is proportional to the square root of the irradiation fluence, which is also consistent with experimental observations. The acceleration method can greatly speed up the simulation of helium irradiation by omitting the helium injection process, which makes it possible for molecular dynamics to simulate the formation of fuzz.