UCL Department of Space and Climate Physics


Cryogenics Research

Our research interests are focused on key technology components in the development of milli-Kelvin cryo coolers. At the present time this is heat switches and the miniaturization of the cooling technology.

Many cryogenic systems require heat flow to be controlled. Heat switches provide this control, allowing thermal isolation and connection between different system components. An ‘ideal’ heat switch would provide complete thermal isolation in its ‘open’ state and a strong thermal link in its ‘closed’ state. Complete isolation can only be achieved using mechanical heat switches, which are undesirable for use in space due to the potential for failure.

We are investigating the construction and peformance of solid state heat switches utilizing the magnetoresitive properties of tungsten.

Research Area: Magnetoresistivity

Magnetoresistivity is where the electrical resistance (i.e. its resistivity and thus the electron flow) is affected by the application of a magnetic field.  As electrons carry energy this equates to a modification in the thermal energy transported in the material (i.e the thermal conductivity). A large change in thermal conductivity (several orders of magnitude) can be obtained by the application of a magnetic field in the 1 to 2 Tesla region.  We are investigating the thermal magnetoresistivity of tungsten to act as a solid state heat switch for our ADRs.

Tungsten thermal conductivity
The pictures show:
  1. The difference in thermal conductivity for one of our tungsten switches with a magnetic field of 1.8 Tesla "off" and zero magnetic field "on"
  2. The as grown tungsten crystal rod
  3. A completed tungsten heat switch with mounting flanges.  This is cut from the solid rod by electron discharge machining (EDM).
A Tungsten magnetoresistive heat switch

A Tungsten magnetoresistive heat switch

Tungsten single crystals

Tungsten single crystals

As grown tungsten rod

As grown tungsten rod