SCUBA-2 warm after 8-months of continuous operation


It doesn’t seem that long ago when one of our major concerns with the SCUBA-2 project was the reliability of the fridge. In March, earlier this year, we installed a liquid Helium cold trap with the aim that it should filter out any contaminants that may have inadvertantly entered the He/He-3 gas mixture.

It’s astonishing how well this has worked. As the graph above shows, the fridge has kept its temperature all the way through the last 8 months, allowing us to control the temperature of the arrays at about 0.09 K. Furthermore, consider that the fridge was designed to only ever be cold for 6  months at a time.

So just this week, we initiated a controlled warm up of SCUBA-2 so that we can carry out some essential maintenance on the refrigeration system. We will be cooling the instrument back down in a few weeks and be ready for more observing with SCUBA-2 at the start of December.

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3 Responses to SCUBA-2 warm after 8-months of continuous operation

  1. Anonymous says:

    Excellent change to the fridge reliability and stability.. Hope maintenance goes well.

  2. Anonymous says:

    Why a liquid helium cold trap? Surely a liquid nitrogen trap would suffice and be cheaper to run.

    • Antonio says:

      The instrument itself is cooled by a mixture of liquid Helium-4 and the much rarer Helium-3, in what’s called a dilution refrigerator. In this way, we can get down to the low temperatures we need (~ 50-100 mK) to operate the arrays. Since Helium has the lowest boiling point of all the gases, including Hydrogen, any contaminant that isn’t Helium could freeze within the system and cause a blockage. So we have to run the trap at liquid Helium temperatures to purify the gas mixture and prevent blockages. This has been a very successful technique for us.

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