The MOONS cryostat has arrived in Edinburgh – and it’s big. This is a key milestone for the project and allows much of the major assembly to really get under way.

IMG_4612.JPG
The cryostat on its side with one of the panel doors removed. The lead technician George is standing inside making measurements before the installation of the optical bench. The removed door can be seen to the right of the image.

MOONS will be unique in providing wavelength coverage out to 1.8 microns, with a high multiplex. But this comes at a cost: to work at these wavelengths the entire spectrograph must be cooled to 130 K, while the multiplexing leads to large optical beams. Both of these factors result in this huge cooled vacuum vessel. We believe that MOONS will have the largest cryostat yet used in any astronomical instrument – although we are happy to be corrected on this, so please let us know!

 

The MOONS vessel in numbers:

  1. Internal Volume: 16m3
  2. Dimensions: 4m x 2.6m x 2.4m
  3. Mass: 3100kg
  4. Operating pressure: <1×10-6 mBar resulting in 400 tonnes of vacuum loading

 

Cooling this beast

We will use liquid nitrogen to precool the system and then closed-cycle coolers to maintain the bench temperature and to provide the lower temperatures required for the infra-red detectors (40K). Cooling a cryostat of this size is challenging: we will need around 4 tonnes of liquid nitrogen per cool down! We require new infrastructure at the ATC to store this much coolant and so progress is also well underway for installing a new nitrogen Dewar outside the main lab.

diggers.jpg
The new bunker built into the bank outside the lab to house the new liquid nitrogen vessel needed for the MOONS cryostat.

Next steps

The optical bench, which sits vertically inside the centre of the instrument has already had much of the cooling pipework and heaters installed. This will now be mounted inside the radiation shield, which will in turn be placed inside the MLI blanket, which finally all goes inside the vessel. We are aiming for the first cool down of the system in the next few months and then we can begin installing all the optics.

 

The vessel has been made for MOONS by AS-Scientific. It was a challenging design with two large open-sided doors required to give easy access to both sides of the optical bench.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s