CARMENES (III): an innovative and challenging cooling system for an ultra-stable NIR spectrograph

摘要

The CARMENES project, which is currently at FDR stage, is a last-generation exoplanet hunter instrument to beinstalled in the Calar Alto Observatory by 2014. It is split into two different spectrographs: one works within the visualrange while the other does it in the NIR range. Both channels need to be extremely stable in terms of mechanical andthermal behavior. Nevertheless, due to the operation temperature of the NIR spectrograph, the thermal stabilityrequirement (±0.07 K in 24 hours; ±0.01 K (goal)) becomes actually a major challenge. The solution here proposedconsists of a system that actively cools a shield enveloping the optical bench. Thus, the instability produced on the shieldtemperature is further damped on the optical bench due to the high mass of the latter, as well as the high thermaldecoupling between both components, the main heat exchange being produced by radiation.This system -which is being developed with the active collaboration and advice of ESO (Jean-Louis Lizon)- is composedby a previous unit which produces a stable flow of nitrogen gas. The flow so produced goes into the in-vacuum circuitryof the NIR spectrograph and removes the radiative heat load incoming to the radiation shield by means of a group ofproperly dimensioned heat exchangers.The present paper describes and summarizes the cooling system designed for CARMENES NIR as well as the analysesimplemented.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.