Computational Modelling of Laser-Matter Interaction through EPOCH PIC Code in the Context of Inertial Confinement Nuclear Fusion

The interaction between laser and matter is gaining increasing attention due to its diverse applications. These encompass a wide range of areas, including inertial confinement fusion for energy production, particles acceleration, medical diagnostics, and cancer treatment. Of particular significance is the proton-boron fusion, which offers the advantage of minimal high-energy neutron production, thereby reducing the potential hazard caused by neutron activation of surrounding materials. Therefore, it is important to understand the characteristics of plasmas generated by laser-matter interactions and the specific nature of the laser-matter interaction itself. Computational models and simulations play a crucial role in studying and simulating these phenomena. They are useful to acquire a quantitative understanding of the physical process governing the interaction between laser and matter: laser beam absorption, energy exchange with the target material, particularly between electrons and ions, as well as fusion processes and the ionization of atoms within the target. The aim of the thesis is to simulate the interaction between a laser beam and matter, with the purpose of analyzing the characteristics of the confined plasma and determining the appropriate target configuration to maximize wall absorption. The effects of the target materials and size on the parameters of the generated plasma, as well as the energy absorbed by the target, can be examined. Moreover, since ionization plays a fundamental role in plasma generation, the aim is to assess how different types of ionization affect the quantity of generated free electrons. To achieve this, a Particle-in-Cell (PIC) code has been utilized as a computational tool capable of simulating large systems of interacting particles. The selected software for this purpose is EPOCH, an open-source program. Before simulating the configuration of interest, an attempt was made to replicate the results obtained in previous works to familiarize with the software and ensure the correctness of the methodology. Specifically, the simulations involve the self-heating process that characterizes PIC models, resulting in a non-physical linear temperature increase. It has been demonstrated that this effect can be mitigated by using current smoothing and increasing the number of particles per cell. Additionally, simulations were conducted to test the performance of the collision module in EPOCH. For instance, it has been observed that a non-equilibrium distribution can be thermalized through self-collisions; and an initially anisotropic thermal distribution can be rendered isotropic as a result of collisions. The tool is then applied to simulate several new target configurations suitable for the proton-boron fusion: target composed by various materials among which boron nitride and considering different laser energy densities were analyzed, and the achieved ionizations and absorbed energy were evaluated. Also materials such as aluminum, tungsten and lead were used to demonstrate how the quantity and type of ionized atoms vary with atomic number. Additionally, the variation in absorbed energy with varying incidence angles was demonstrated.