Design, simulation, and testing of the evanescent wave coronagraph prototype port adapter to the Thai National Telescope

The Evanescent Wave Coronagraph (EvWaCo) is a type of Lyot coronagraph that uses an achromatic focal plane mask comprising a lens and a prism in contact. The National Astronomical Research Institute of Thailand (NARIT) plans to install an EvWaCo prototype equipped with an adaptive optics system (AO) to correct the aberrated wavefront in real-time at the unused left Nasmyth port of the Thai National telescope. To prepare for this installation, a large adapter with a diameter of 1.3 m and twelve carbon fiber poles serve as the supporting beams to hold the prototype. This work focuses on the mechanical design and testing of the large adapter, considering the prototype requirements and installation limitations. In particular, mechanical deformations and stress distributions are analyzed under survival conditions. The maximum weight of the prototype is 200 kg, and a folding mirror installed in a translation stage is placed inside the large adapter. The structural optimization uses the finite element method to deal with the constraints and ensures a high performance. The carbon fiber poles comprise carbon fiber-reinforced polymer (CFRP) that reduce the weight by approximately 30% compared to an all-aluminum structure. Each carbon fiber pole weighs about 1.75 kg, and our testing results show that it can support up to eight times the prototype's weight. The epoxy adhesive, used to join different materials, can withstand a pull-out strength of up to three times the prototype's weight. The installation of this adapter is expected to start by the end of 2024.