In laser-induced fluorescence (LIF), measurements of spontaneous light emission after laser excitation of plasma particles provides useful insight into some its qualities, like its ion temperature and wave-particle interaction dynamics.
Usually scientists analyze LIF results with the fixed coordinate-based Eulerian approach. But in an article in Physics of Plasmas, authors apply a Lagrangian approach to LIF analysis using newly written code to follow each individual ion orbit. They found the Lagrangian model, with which they numerically simulated the ion velocity and wave-detection process, is more efficient and revealing than the Eulerian. It computationally allows a separation of the quantized description of ionic states from the classical dynamics of the ion center of mass. Also, some key calculations can be done by hand and included readily, leading to large time savings.
Co-author Frederick Skiff said that using the Lagrangian approach will allow the many physicists conducting LIF to avoid common pitfalls. The Lagrangian interpretation makes it easier to avoid misinterpreting one measurement for another, like the temperature of plasma ions, mistaken for the temperature of neutral particles.
The Lagrangian approach also enables improved analysis of metastable ions. Metastable ions in plasma have two sources: neutral gas particles or other ions in the plasma. According to co-author Feng Chu, the Lagrangian method allows contributions from these two populations to be considered independently, resulting in more easily determining where metastable particles come from, as well as measuring their lifetimes. In addition to this work, the authors plan to continue enhancing their code for more complex applications.
Source: “A Lagrangian model for laser-induced fluorescence and its application to measurements of plasma ion temperature and electrostatic waves,” by F. Chu and F. Skiff, Physics of Plasmas (2018). The article can be accessed at https://doi.org/10.1063/1.5020088.
