AO4ELT5 Proceedings

Direct expansion gas cooling technology applied to the E-ELT M4 adaptive mirror

Pescoller, Dietrich (Microgate), Biasi, Roberto (Microgate), Tintori, Matteo (ADS International), Manetti, Mauro (Microgate), Merler, Alberto (Microgate)

The E-ELT M4 adaptive mirror is based on the voice-coil contactless adaptive mirror technology, with more than 5000 actuators controlling the mirror shape. Its driving electronics is expected to dissipate about 8-9kW, with consequent heat generation. Considering the M4 mirror location inside the telescope optical path, it is very important to minimize the temperature difference between the system and the ambient surrounding it, to avoid the possible introduction of wavefront optical aberrations because of air convection phenomenon. So, a dedicated cooling system is mandatory. Past solutions were based on glycol liquid cooling, which proved to be adequate in terms of performances. However, the given M4 complexity and modularity requirements, together with the constant research of improved system reliability, suggested moving from the actual glycol solution to a direct expansion gas cooling system. The advantages of this new approach are: negligible system damages in case of cooling leakage because of instantaneous gas evaporation, improved overall cooling system efficiency, which in turn allows a very low coolant flow rate, and an improvement of the cooling system performance in terms of system temperature uniformity. Cooling based on direct gas expansion technology is nowadays widely used in several industrial and civil applications. The present work shows experimental tests performed on the E-ELT M4 demonstration prototype, which show that an appropriate implementation of this technology to the adaptive optics instruments can satisfy the stringent system cooling requirements and be potentially applied to other leakage-sensitive instruments.

DOI: 10.26698/AO4ELT5.0123- Proceeding PDF

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