MSc. Prashant Dwivedi

This research investigates the interaction between high-speed tungsten (W) dust and plasma-facing components (PFCs) in fusion reactors, particularly focusing on W walls. Through molecular dynamics (MD) simulations, the study covers a broad spectrum of W dust velocities to evaluate their effect on wall materials with various crystal orientations. We found that high-speed impacts cause considerable damage, including sputtering, degradation, and deformation. The study introduces a damage model derived from experimental and simulation data that reveals the patterns and mechanisms of damage caused by dust impacts. The proposed model significantly improves our understanding of dust-wall interactions and underscores the importance of MD simulations as a reliable technique for exploring such phenomena in the challenging conditions of fusion devices. These insights are crucial to predict and mitigate damage to PFCs, helping to develop more resilient and efficient components. Overall, the research offers valuable knowledge on the atomic-level dynamics of dust impacts and represents a notable advancement in the durability and efficiency of materials used in fusion energy technologies.

The atomistic mechanisms of damage initiation during high velocity (v up to 9 km s(-1), kinetic energies up to 200 keV) impacts of W projectiles on a W surface have been investigated using parallel molecular-dynamics simulations involving large samples (up to 40 million atoms). Various aspects of the high velocity impacts, where the projectile and part of the target material undergo massive plastic deformation, breakup, melting, and vaporization, are analyzed. Different stages of the penetration process have been identified through a detailed examination of implantation, crater size and volume, sputtered atoms, and dislocations created by the impacts. The crater volume increases linearly with the kinetic energy for a given impactor; and the total dislocation length (TDL) increases with the kinetic energy but depends on the size of the impactor. We found that the TDL does not depend on the used interatomic potential. The results are rationalized based on the physical properties of bcc W.

In recent years, computer simulations have played a fundamental role in unveiling some of the most intriguing features of prime numbers. In this paper, we define an algorithm for a deterministic walk through a two-dimensional grid, which we refer to as a prime walk. The walk is constructed from a sequence of steps dictated by and dependent on the sequence of the last digits of the primes. Despite the apparent randomness of this generating sequence, the resulting structure-in both two and three dimensions-created by the algorithm presents remarkable properties and regularities in its pattern, which we proceed to analyze in detail.