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The Daniel K. Inouye Solar Telescope (DKIST) was recently commissioned on the Pacific island of Maui. The 41.5 metre high telescope is the world’s largest of its kind and enables scientists to observe the solar surface more closely than ever before. A major challenge in the design of the DKIST was in minimizing the thermal energy absorbed by the focus on the sun. For a special heat absorption system, Aavid Thermacore – the specialist thermal technologies contractor – relies on solutions from the #siemens Digital Industries Software portfolio. In this way, the thermal energy is reduced from 2.5 megawatts per square metre to just 300 watts. The engineers were also able to ensure that the resulting heat does not degrade the image quality.
Unlike space telescopes, which are used at night-time, the DKIST will spend its working life pointing directly at the sun. This means that the solar telescope is exposed to large quantities of heat energy. A “heat stop” is therefore an integral component of this type of telescope. It is located at the prime focus and prevents large amounts of undesired sunlight from reaching the subsequent optics. The heat stop is cooled using an internal system of porous metal heat exchangers, which dissipate around 1700 watts at peak operating load. Another challenge for the designers was avoiding a phenomenon known as “self-induced seeing”. In this phenomenon, thermal influences and wind degrade the image quality, similar to the effect of high temperatures in the desert where the horizon appears to “flicker”. To prevent this, engineers had to ensure that the heat stop did not have a thermal influence on the optics. The temperature of the “heat stop” must therefore never be more than ten degrees Celsius higher than the ambient air.
When designing the heat stop, the experts at Aavid Thermacore had to take into account multiphase flow within the metal heat exchangers and ensure that, for example, asymmetrical thermal load would not result in “hot spots”, which in turn could cause the “self-induced seeing” phenomenon. By using #siemens Star-CCM+ software, Thermacore engineers were able to visualize flow patterns within the enclosure and adapt the design accordingly. They also succeeded in designing the heat stop so that its temperature is not more than ten degrees Celsius above ambient temperature.
Better understanding of the sun
With this ultra-modern cooling system, the scientists are now able to use the DKIST to its full capacity. The 75-millimetre thick primary mirror has a diameter of 4.24 metres and provides extremely sharp images of the solar surface. One of the research aims is to learn more about the magnetic fields of the sun, which control the temperature of the corona and the solar wind. As a result, the scientists hope to improve their predictions on the way in which this space weather influences the earth.
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