13 September 2012 Overall performance of the ALMA antenna during solar observation
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Abstract
The Atacama Large Millimeter Array (ALMA) consists of a large number of 12m diameter antennas that will operate up to 950GHz. The antenna must meet all primary operational performances also during solar observation. When the antenna is pointing directly the sun or when the sun is close to the boresight axis, the solar power concentrated by the mirrors cannot damage any part of the antenna. When the antenna is pointing toward the sun, the power absorbed by a black body positioned in the secondary focal area shall not exceed 0.3 W/cm2. To achieve these requirements, the primary surface of the antenna has a suitable surface scattering treatment. The same thing was done for the surface of the subreflector. Specific tests were performed on the panels surface and secondary mirror during the prototype and production phase in order to optimize the best behaviour. A particular care must be applied in the control of the secondary area, where the entire solar power spectrum, from the UV to the infrared, reflected by the primary mirror, can contribute to overheat reflecting areas support structures. In this report we provide a series of analysis and results obtained during the solar observation.
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A. Busatta, A. Busatta, A. Brunelli, A. Brunelli, F. Rampini, F. Rampini, G. Marchiori, G. Marchiori, } "Overall performance of the ALMA antenna during solar observation", Proc. SPIE 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 845006 (13 September 2012); doi: 10.1117/12.927137; https://doi.org/10.1117/12.927137
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