Speaker
Description
Laser-Induced Breakdown Spectroscopy (LIBS) is a versatile laser-based diagnostic technique that enables rapid elemental and isotopic characterization of materials through the analysis of optical emission from a laser-induced plasma. Thanks to its intrinsic features – such as remote detection, the absence of sample preparation, and the capability to work under harsh environmental conditions (including the presence of plasma and magnetic field) – LIBS is considered a promising diagnostics tool for in-situ monitoring of Plasma Facing Components (PFCs) in magnetic confinement fusion devices. In particular, it offers significant potential for investigating impurity deposition and hydrogen isotope retention, which are critical issues for the development of future fusion reactors.
This presentation summarizes the Ph.D. research activities carried out within the framework of the NEFERTARI project, a national initiative funded by Next Generation EU aimed at upgrading laboratories and experimental infrastructures for nuclear fusion research in Padova, Bari, and Milano. The doctoral project focused on preparatory activities aimed at supporting the implementation of an in-situ LIBS diagnostic on the upgraded BiGyM Linear Plasma Device (LPD), located at CNR-ISTP Milano.
A preliminary diagnostic layout was defined based on a literature review of LIBS applications in fusion environments and on sensitivity analyses performed on simple LIBS spectra. A picosecond Nd:YAG laser source and a compact high-resolution spectrometer (Isoplane 320 monochromator coupled to a PI-MAX 4 ICCD camera, Princeton Instruments) were identified as suitable components for a LIBS system mainly devoted to fuel retention studies. In addition, a conceptual optical path for coupling the laser system to the LPD was designed.
A major contribution of this work was the development of a numerical model of the laser ablation process, conceived as a predictive and interpretative tool for LIBS applications. The modeling activity, implemented using COMSOL Multiphysics, initially focused on the nanosecond pulse regime, which is widely adopted in fusion-related studies. The model describes laser energy deposition, heat transfer, phase transitions, and material removal mechanisms, enabling the prediction of ablation crater depth and diameter, as well as the temporal evolution of temperature within the target. The framework was subsequently extended to the picosecond regime through the implementation of a Two-Temperature Model, allowing separate treatment of electron and lattice subsystems and providing insight into non-equilibrium heating dynamics. Model predictions for both regimes were validated against dedicated laser irradiation experiments on tungsten and silicon, showing good agreement in terms of crater morphology and dimensions.
In addition, in-situ LIBS experiments for short-term deuterium retention measurements were performed on the PSI-2 LPD during a visiting period at the Forschungszentrum Jülich. These measurements provided practical insight into hydrogen isotope detection in fusion-relevant materials and enabled the extraction of short-term retention data and their temporal evolution for tungsten and tantalum, the latter being a potential alternative to tungsten for PFC applications. Furthermore, results from Nulcear Reaction Analysis (NRA) measurements, providing absolute concentration values and depth profiles for the two materials, are also reported.
Overall, the results discussed in this work provide a consistent framework that integrates diagnostic design, numerical modeling, and experimental validation. This combined approach supports the future implementation of an in-situ LIBS system on BiGyM and contributes to the development of a reliable diagnostic tool for plasma–material interaction studies under fusion-relevant conditions.