Mechanical Design

EMIR will be attached to the mechanical rotator and platform of the Nasmyth- focus (GTC). The instrument is supported from the rotator by the Nasmyth Rotator Adapter (NRA) and from the platform by the Nasmyth Platform Adpater (NPA). This attachment causes the whole instrument to rotate together with the Nasmyth rotator. The NPA helps holding the instrument, providing additional rigidity to minimize the effects of flexure and extra support for the huge EMIR mass (in excess of 4Tons).

 

    

The mechanical layout of the instrument has been derived from the optical design, taking into account the Nasmyth space envelope. Two flats mirrors have been added to bend the beam and a cold optical bench has been optimized to fulfil the image stability error budget. When the light beam enters the cryostat through the Cryostat Window it first passes through the Radiation Baffle which rejects back out stray light, thus limiting the incoming radiation. The beam then encounters the Configurable Slit Unit (CSU), a remotely controlled mechanism capable of generating different patterns of multislits, long slits and free aperture at the focal plane. One step beyond, the light crosses the first Collimator Barrel, and then enters through the Periscope where the beam is folded twice by means of flat mirrors. Right at the exit of the Periscope, the second collimator barrel precede the Grisms Wheel, which carries multiple dispersive elements that can be remotely selected and introduced in the light path. Then the Camera Barrel guides the light to the Filters Wheel, finally reaching the Detector Assembly (DA) which is mounted onto an XYZ mechanism, the Detector Translation Unit (DTU).


 

The structural mainframe of the cold part of the instrument is the Optical Bench which holds and cools the optomechanical components of EMIR; a geometrically complex and passive Cold Shields is used to reject unwanted thermal radiation. The Optical Bench is supported and thermally isolated from the warm Vacuum Chamber by means of six isostatically mounted Radial Support Trusses and three Axial Support Trusses. The cryo–coolers attached to the Vacuum Chamber are thermally linked to the cold structure, and keep it at cryogenic temperature. There is also an additional cooling system consisting of Liquid Nitrogen Tanks attached to the optical bench, that can be filled and evacuated from the outside via special pipeworks. These will be used for the precooling of the instrument.