The heat stop for the 4-m European Solar Telescope EST

A study is presented for the realization of the heat stop for the 4-m European Solar Telescope EST, whose feasibility study will be completed in 2011. EST is an on-axis Gregorian telescope, equipped with a four-meter diameter primary mirror and primary focal length of about six meters. The heat stop, positioned at the primary focus, must be able to remove a heat load of 13 kW, while maintaining its surfaces very close to room temperature, to avoid the onset of seeing. In order to remove the heat, three configurations have been taken into consideration: 1) a flat 45 degrees inclined heat rejecter, 2) a 45 degrees conical heat rejecter and 3) a heat trap (made of a conical heat rejecter and a cylindrical heat absorber). All devices include an air removal system to avoid the formation of thermal plumes.