An overview of the evolution of the modeling of reflectometry diagnostics in fusion plasmas using finite-difference time-domain codes

Microwave reflectometry, having its origins in ionosphere probing techniques to evaluate electronic density, has become one of the most important diagnostics for the same quantity in fusion plasmas. Reflectometry will play a major role in next-generation machines, in particular in DEMO, where it is expected to provide plasma positioning, shaping, and tracking data. The ability to have an ever-increasing comprehensive description of reflectometry is particularly important since it allows us to assess the measuring capabilities of existing experimental systems and to predict the performance of new diagnostic concepts based on probing waves. Furthermore, wave propagation in a thermonuclear plasma with fluctuating electronic densities is far from straightforward and the need for a numerical full-wave treatment becomes fundamental. We will present the reader with the fundamentals of this technique and introduce the usage and evolution of FDTD in reflectometry, using as an example, the synthetic diagnostics setup that uses the family of REFMUL* codes, which is employed in the assessment of the performance of several reflectometry systems in different fusion machines.