EST, the European Solar Telescope, is a pan-european project, presently in its Conceptual Design Study financed by the European Commission, involving 29 partners, plus 7 collaborating institutions, from 14 different countries.
EST is a 4-meter class solar telescope, to be located in the Canary Islands. It will be optimized for studies of the magnetic coupling between the deep photosphere and upper chromosphere.
This will require diagnostics of the thermal, dynamic and magnetic properties of the plasma over many scale heights, by using multiple wavelength imaging, spectroscopy and spectropolarimetry. To achieve these goals, EST will specialize in high spatial and temporal resolution using instruments that can efficiently produce two-dimensional spectral information.
Our group is responsible of work-package WP-5300 (Heat Rejector) and it is participating in Wavefront Reconstruction work-package.
Heat Rejector: In such a large collecting area solar telescope a considerable heat load (13 kW) is concentrated by the primary mirror on the focal plane image (of about 60 mm of diameter). It is thus necessary to place a heat stop at the primary focus ith the purpose of selecting the desired field of view (a few minutes of arc) and of preventing the remaining solar radiation (about 99 %) to reach the subsequent optics. The unwanted solar radiation must be disposed of by absorbing it or reflecting it away.
Given the on-axis Gregorian layout of the EST telescope, where the primary focal plane lies between the primary and the secondary mirror, only a small volume is available in the neighbourhood of the focal plane for installing heat stop device without blocking the light paths. This limitation rules out the possibility of a cooled device capable to absorb entirely the heat flux, imposing a solution based on a reflecting element.