Assessment and performance optimization of the ITER plasma position reflectometry in-vessel oversized waveguide bends

Highlights: • Assessment for the 90° bend of the GAP 4 and 6 of the ITER PPR. • Optimization using a hyperbolic secant function. • We assess the electromagnetic performance for the 120° bend of PPR. - Abstract: The ITER plasma position reflectometry system is composed by five reflectometers distributed at four locations, known as gaps 3–6, operating in O-mode in the frequency range 15–75 GHz. Here we consider only the systems of gaps 4 and 6. To reduce losses, the in-vessel transmission lines use oversized rectangular waveguides whose dimensions are imposed by space availability. As the waveguides are welded to the vessel wall, its routing has to adjust to the vessel geometry. To cope with these constraints, the transmission lines of both gaps feature two 90° bends, behind the blanket modules, just before/after the launching/receiving antenna. Additionally, gap 4 features two 120° bends located at the vessel-to-port transition. Oversized bends are critical components, which can lead to increased losses by mode conversion, making it crucial to assess and optimize their electromagnetic performance. Here, the performance of the 90° and 120° bends is studied trough numeric simulations using ANSYS HFSS. For the 90° bend, results show an increase in electromagnetic performance through the adoption of a hyperbolic secant geometry. For the 120° bend, the preliminary results indicate that an adequate electromagnetic performance might also be achievable.