Many areas of scientific research require instruments that operate at
temperatures of 77 K (-196 C) and below, usually referred to as cryogenic
temperatures. Sometimes temperatures of 0.1 K or even lower are necessary.
Current knowledge of the behaviour of materials at cryogenic
temperatures is somewhat limited. There are many materials that would
be likely to be of great use if the thermal and mechanical properties
were better known. Even for supposedly well known materials, our
knowledge is often based on a very limited set of
measurements. Furthermore, these measurements were often made decades
ago, at which time the composition of nominally identical alloys and
polymers may have been sufficiently different to cause large
differences in behaviour at low temperatures.
The usual solution to the lack of knowledge is to construct cryogenic
instruments from a small number of materials with the best known
properties.
This can result in over-engineered instruments, a solution which can be
acceptable for ground-based instruments but is a serious penalty for
space-based instruments.
Where it is not possible to use known materials, or if the
demands are too critical to rely on existing knowledge, further
measurements are required.
The intial design is carried out with estimated values, with measurements
then made in the hope that they will confirm the estimates.
Due to tight time-scales, this often results in rushed experiments made
in equipment which is not designed for this purpose, and the results
can be of doubtful quality. Furthermore, while such an approach can be
sensible for a small scale instrument, it is
less appropriate for large instruments built
over several years at a cost of tens of millions of pounds. Here, the
impact in terms of money and delays is high if a material is discovered
to be unsuitable,
forcing a redesign and probably
a new measurement programme on a replacement material.
For the same reason, there
is limited scope for innovative design. There is therefore a need for
instrument development to be decoupled from research into materials
and techniques for building such instruments. As instruments become larger
and more complex, and resources more constrained, such an approach is
becoming increasingly important.
