A: Microwave reflectometry is the prime candidate to measure the DEMO plasma position and shape. DEMO will be based on a pre-defined operation scenario, allowing the optimization of the reflectometry measurements according to the expected parameters. When evaluating the system performance for the expected baseline scenario, it is essential to take into account the e ects of the plasma displacement, of the turbulence and of the MHD activity in the measurements. Therefore, the design of the DEMO plasma position reflectometer (DEMO PPR) involves the assessment of the measurement performance of di erent poloidal views, antenna assemblies, emitting angles and di erent plasma configurations. In this work we evaluate the measurement performance over 100 di erent poloidal positions of the DEMO PPR using a synthetic monostatic O-mode reflectometer. The antennas were initially aligned perpendicularly to the wall. The results show that most of the locations at the top of the machine and near the divertor are not adequate for measuring the plasma position. These locations are characterized by larger wall-plasma distances and by larger angle of incidence on the separatrix. In order to optimize the measurement performance of the system, the antennas were aligned perpendicularly to the expected separatrix position, reducing these parameters. With the exception of the locations near the divertor, this geometrical consideration improved the measurement performance for all the positions, placing them below the requirement for the plasma positioning (⇠ 1 cm). The locations near the divertor lose the signal due to the significant plasma curvature before the separatrix. We also studied the e ect of a vertical plasma displacement of z = ±5 cm in the measurements. The results show that the system is stable, fulfilling the chosen requirements. Aligning the emission perpendicularly to the separatrix proved to be a necessary condition in the optimization and stability of the DEMO PPR system.

We conducted a first assessment of the measurement performance of the in-vessel components at gap 6 of the ITER plasma position reflectometry with the aid of a synthetic Ordinary Mode (O-mode) broadband frequency-modulated continuous-wave reflectometer implemented with REFMUL, a 2D finite-difference time-domain full-wave Maxwell code. These simulations take into account the system location within the vacuum vessel as well as its access to the plasma. The plasma case considered is a baseline scenario from Fusion for Energy. We concluded that for the analyzed scenario, (i) the plasma curvature and non-equatorial position of the antenna have neglectable impact on the measurements; (ii) the cavity-like space surrounding the antenna can cause deflection and splitting of the probing beam; and (iii) multi-reflections on the blanket wall cause a substantial error preventing the system from operating within the required error margin.

A: Reflectometry is foreseen in the coming generation of tokamaks such as DTT, ITER and DEMO, creating a need to predict the behavior and capabilities of these new reflectometry systems through the used of synthetic diagnostics. The FDTD time-dependent codes use to implement synthetic diagnostics are computational demanding, the reason why 2 dimensional codes (as REFMUL or REFMULF) are used. REFMUL3, a newly developed performing parallel code gives access to 3D simulations, although at a much higher cost than the 2D ones. With this work we begin a benchmark effort to assess the main differences and compromises done when using 2D versus 3D. K: Simulation methods and programs; Plasma diagnostics -interferometry, spectroscopy and imaging 1Corresponding author.

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