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

  Becerril Jarque, S.
  et al.
  
  Paper 8450-168 of Conference 8450
  Date: Tuesday, 03 July 2012 
  
  The CARMENES project, which is currently at FDR stage, is a last-generation
  exoplanet hunter instrument to be installed in the Calar Alto Observatory by
  2014. It is split into two different spectrographs: one works within the
  visual range while the other does it in the NIR range. Both channels need to
  be extremely stable in terms of mechanical and thermal behavior. Nevertheless,
  due to the operation temperature of the NIR spectrograph, the thermal
  stability requirement (±0.07K in 24 hours; ±0.01K (goal)) becomes actually a
  major challenge. The solution here proposed consists of a system that actively
  cools a shield enveloping the optical bench. Thus, the unstability produced on
  the shield temperature is further damped on the Optical Bench due to the high
  mass of the latter, as well as the high thermal decoupling 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 composed by a previous unit which produces a stable
  flow of nitrogen gas. The flow so produced goes into the vacuum tank of the
  NIR spectrograph and removes the radiative heat load incoming to the radiation
  shield by means of a group of properly dimensioned heat exchangers. The
  present paper describes and summarizes the cooling system designed for
  CARMENES NIR as well as the analyses implemented.