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NASA Goddard Space Flight Center
Cryogenics and Fluids Branch

Research and Development Programs

Here are the subjects where we expect to concentrate our future technology development:

Mechanical Coolers

Mechanical coolers offer the possibility of longer lifetimes than the stored cryogen coolers that have been used in the past. (One example of a stored cryogen cooler is the liquid helium dewar on COBE.) The disadvantage of stored cryogens is that they stop cooling as soon as their supply of cryogen (such as liquid helium) is exhausted.

Adiabatic Demagnetization Refrigerators (ADRs)

ADRs are magnetic coolers, especially useful in the range near absolute zero. For example, and ADR designed for the X-Ray Spectrometer (XRS) could cool to 60 milliKelvin for 30 hours. Among the advantages of the ADR are that it is highly efficient and can be built with no moving parts and no need for a liquid handling system. For details of how the ADR works see the ADR primer. For a less technical version, see the Introduction to the ADR. An ADR has a limited temperature range. That is, the ADRs that we use at temperatures near absolute zero must work with another cooler to bridge the gap between room temperature and the "hot" end of the ADR. For example, the "hot" end of XRS ADR was connected to a tank of liquid helium at 1.3 kelvin.

Continuous ADR (Advanced ADR)

The advanced ADR, which we are developing now, will be a multi-stage ADR. As with the conventional ADRs we have developed, the cold end will be at millikelvin temperatures. The "hot" end, however, will be at 10 kelvin, much warmer than was the case with our conventional ADRs.

Among the advantages of the Advanced ADR are:

  • its high-end temperature of 10 kelvin will be warm enough to use a mechanical cooler as a heat sink;
  • it will be able to run continuously, without the pauses for cycling required by standard ADRs;
  • it will be lighter in weight than conventional ADRs intended for long hold time use.

The multi-stage nature of the Advanced ADR allows it to run continuously. A conventional ADR must warm up periodically to dump the heat it has absorbed from the objects it's cooling. This need to warm up can be inconvenient. In the X-Ray Spectrometer (XRS), for example, observations would be interrupted during warmup, because the astronomical sensors would not work at the higher temperature. In the Advanced ADR, however, the cold-end stage of the ADR would never warm up. Instead, the second stage would cool the end stage by dropping to a lower temperature.

The XRS ADR was designed with enough thermal storage ability to absorb heat continuously for 30 hours. The cold end stage of the Advanced ADR need only have a fraction as much heat storage ability, since it will be repeatedly cooled by the second stage. Therefore, the cold end stage can be a fraction of the weight of the XRS ADR. The other stages of the Advanced ADR can likewise be small, because they can go through the warm part of their cycle as often as necessary without disturbing the astronomical sensors, or other objects being cooled.

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