Ultra Low Temperature Cryogenic Physics - The thermal transport in micro structures at very low (milli-Kelvin) temperatures: Dr. Ian Hepburn

Future astronomical space missions will be using cryogenic x-ray and sub-millimetre wave detectors operating in the 50 - 100 mK region. The adiabatic demagnetisation refrigerator (ADR) is the preferred method of cooling to these temperatures. MSSL has a long history of ADR development for space, delivering to the European Space Agency (ESA) in 2008 the worlds first space flight worthy ADR capable of being cooled by current space cryo-coolers, eliminating the need to carry in the spacecraft large quantities of liquid helium which limit mission duration. Current ADR systems are bulky and relatively heavy. The development at MSSL of key technologies e.g. new heat switches (magnetoresistive heat switches utilizing high purity single crystal tungsten), the tandem ADR concept and the prospect of fast ramp rate superconducting magnets offer the potential to reduce the ADR size by many orders of magnitude, potentially down to the micron size. The control of heat is a vital factor in the ADR operation which at milli-kelvin temperatures is non trivial due to electron and phonon scatter in materials and at material boundaries. It is important to have a full understanding of all thermal transport mechanisms at very low temperatures in order to be able to realise the possible next generation of milli-kelvin space coolers. This Ph.D project will investigate both theoretically and experimentally (using the cryogenics group well equipped cryogenics labs containing several milli-Kelvin ADR coolers, 4 K pulse tube cryo-coolers and associated electronics for low temperature research) the physics of thermal transport at very low temperatures and apply this to the design of a micron sized ADR cooler for future utilization in cooling detectors for space and ground based applications.

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