Towards a Micro milliKelvin Cooler Array

This application seeks to demonstrate a 4 K to millikelvin micro cooler through the demonstration of a new concept. Low temperature cryogenics has always been a relatively large scale technology i.e. dilution refrigerators and adiabatic demagnetisation refrigerators (ADR). Recent advances at MSSL in the millikelvin cryocooler (mKCC), solid state heat switches and magnet design enables a new concept of cooling in the 4 K to millikelvin region which enables a dramatic reduction in size. For example, the mKCC which provides 1 uW of cooling power at 100 mK, could be reduced from 5.6 (d) x 12 (w) x 30 (h) cm to a size of 4 (d) x 5 (w) x 5 (h) cm by using the new micro cooler concept. The ultimate coupling of this millikelvin micro cooler to higher temperature micro coolers, offers the prospect of a complete 300 K to 100 millikelvin micro cooler that could be used to cool state-of-the-art cryogenic detectors (e.g. Microwave Kinetic Inductance Detectors MKIDs) and quantum computers in a very compact, portable system. In this application we seek the funds to demonstrate this concept by constructing a small prototype system which will have a continuous 100 mK cooling power of 0.3 uW, when interfaced at 4 K and have predicted dimensions of only 3 x 2 x 5 cm. This concept enables very easy adaptation for higher cooling powers and lower temperatures.

Low temperature cryogenics is a critically important enabling technology of commercial significance that can be exploited in a number of different fields e.g. detector systems (medical and security), scientific instrumentation and computing (quantum computing), with the key requirements being compactness and ease of use. It is important that users and instrument developers no longer have to be specialists in ultra low temperature (ULT) technologies in order to use it. For applications using low temperatures (e.g. cryogenic detectors) outside the specialist research domain e.g. security and medical imaging, the cooling technology needs to be small and invisible to the user. Technology miniaturization, especially on a scale enabled by the proposed project, will provide significant increase to commercial opportunities and scientific capabilities. The potential of a complete micro cooler from 300 K to millikelvin offers the prospect of portable systems, which is a vision unheard of before the prospect of micro coolers and this application. In a recent article by J Ullom, of the National Institute of Standards and Technology (NIST) "Will ultralow temperatures leave the research lab", Cryogenic society of America, (1/4/2013) (http://www.cryogenicsociety.org/csa_highlights/will_ultralow_temperatures_leave_the_research_laboratory/), he states, "Subkelvin sensors are under development for a wide range of applications, including precision x-ray, gamma-ray and alpha-particle spectroscopy for materials analysis, optical photon-counting for advanced telecommunications and submillimeter or THz sensors for concealed weapons detection". "Peering into the future, .... the use of ULTs will become even more widespread. Further dissemination will require a combination of motivating applications and the existence or development of refrigeration technology suitable for these applications." "ADRs are generally attractive; their operating principle is very simple, they use no fluids and they require very little supporting hardware". The miniaturized continuous cooling technology proposed in this application will have an impact. The reduction in size of the 4 K to 0.1 K cooling element to a few centimeters in size is a first step in the realization (combined with higher temperature micro coolers in the future) of an unparalleled opportunity to reduce the size and complexity of a technology in which so far has been complex in operation and large. Miniaturisation will enable low temperature devices from the research lab to be much more easily moved into the applications and commercial world. In summing up Ullom states in his article "However, whether the dissemination of ULTs will truly be widespread depends on whether large cost reductions are possible in the future or whether large simplifications in the cooling process can be achieved". The micro cooler presented here will achieve a high proportion of the path to simplification of cooling. The UK has a very strong commercial low temperature industry comprising both large (i.e. Oxford Instruments) and several SMEs (e.g. ICEOxford, Cryogenics, Scientific Magnetics etc). The proposed cooler development will provide a technological enhancement to them and enable the UK to capitalise on emerging markets for low temperature devices in the areas described in the proposal due to our proposed simple micro cooler.