7 August 2014 Aero-thermal simulations of the TMT Laser Guide Star Facility
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Abstract
The Laser Guide Star Facility (LGSF) system of the Thirty Meter Telescope (TMT) will generate the artificial laser guide stars required by the TMT Adaptive Optics (AO) systems. The LGSF uses multiple sodium lasers to generate and project several asterisms from a laser launch telescope located behind the TMT secondary mirror. The laser beams are transported from a location below the primary mirror to the launch telescope using conventional optics to relay the beams along the telescope structure. The beams and relay optics are enclosed into hermetic ducts for safety reasons and to protect the optics against the environment. A Computational Solid Fluid Dynamics (CSFD) model of the LGSF ducts has been developed. It resolves the duct thickness, laser beam transfer lenses, mirrors and their framework for most of the laser beam path that is subject to significant temperature gradients and/or large vertical change. It also resolves the air inside the duct and its thermal interaction with the aforementioned components through conjugate heat transfer. The thermal interaction of the laser beam with the optics is also captured. The model provides guidance to the LGSF design team and a first estimate of the laser beam stability performance and requirement compliance. As the telescope structure design has evolved in the recent years, a new optical path has been proposed for the LGSF. Both the original and the new optical paths are compared against optical, mechanical and other telescope performance related criteria. The optical performance criteria include a first order analysis of the optical turbulence generated within the ducts. In this study simulations of the thermal environment within the ducts of the two candidate paths are performed and conclusions are drawn.
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Konstantinos Vogiatzis, Konstantinos Vogiatzis, Corinne Boyer, Corinne Boyer, Kai Wei, Kai Wei, Jinlong Tang, Jinlong Tang, Brent Ellerbroek, Brent Ellerbroek, } "Aero-thermal simulations of the TMT Laser Guide Star Facility", Proc. SPIE 9148, Adaptive Optics Systems IV, 914868 (7 August 2014); doi: 10.1117/12.2057208; https://doi.org/10.1117/12.2057208
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