explain how low temperatures are produced using adiabatic demagnetisation
The adiabatic demagnetization refrigerator (ADR) systems from Janis Research offer a simple method of achieving temperatures of 50 mK. These systems make use of two built in pills that operate at temperatures of 1 K and 50 mK, supported below a 4 K surface that is cooled with either liquid helium or a mechanical (pulse tube) cooler. These systems offer a typical hold time of two to three days below 100 mK, and require no active pumping on the cryostat. A recycling period of two to three hours is needed at the end of the three day period, to reduce the temperature back to 50 mK.
These systems include a conductively cooled superconducting magnet, which is used to magnetize the two pills, and a mechanical heat switch that links and isolates the two stages from the 4 K surface. After magnetizing the pills at 4 K, the pills are isolated from the 4 K surface and demagnetized to achieve the lowest temperature. The cold stage may then be allowed to drift up in temperature or controlled to operate at any higher temperature between 50 mK and 150 mK.