The Small Lancaster Nuclear Cooling Cryostat
The smallest of the Lancaster nuclear cooling refrigerators, built in 1988, is centred on a 2.7 mK dilution refrigerator built in Lancaster1. The cryostat is supported on a tripod of concrete pillars, in total weighing 4.5 tonnes. To reduce the influx of unwanted heat energy as much as practically possible, two strategies are used. Firstly, to provide vibrational isolation from the building (and the nearby motorway!), air springs are used to lift the concrete pillars away from the floor. Secondly, the whole apparatus is built inside an electrically shielded environment - a Faraday cage - to reduce electromagnetic pickup. All the necessary heavy power equipment (pumps etc) is situated outside the room.
To achieve temperatures down to ~100 μK, we use our standard Lancaster designed, single shot copper nuclear demagnetisation stage2. The magnetic field is provided by a commercial 8 Tesla superconducting magnet with a 90mm bore. The stage cools 3He-B at zero pressure to around 110 μK, maintaining temperatures below 150 μK for up to two weeks.
Recent experiments have included measurements on vibrating wire generated quantum turbulence; aerogel immersed in superfluid 3He-B; particle detection with superfluid 3He-B; and the low temperature properties of tunnel junctions.
1. D. I. Bradley et al, Cryogenics 34, 549, (1994)
2. D. I. Bradley et al, J. Low Temp. Phys. 57, 359, (1984)
