Airborne Gravity 2010 - Geoscience Australia

Airborne Gravity 2010
Cryostat
The cryostat performs two functions; it supports the instrument mechanically when subject to aircraft
flight loads, as well as providing the low-temperature environment that the instrument needs in order
for various components within it to superconduct. This low temperature is achieved through the use of
a liquid helium reservoir, within which an evacuated can containing the instrument is submerged, thus
keeping the instrument at a temperature below 5 K. A dewar-type construction is used to insulate the
liquid helium reservoir from ambient temperatures. A key performance target for the cryostat is the rate
of helium boil-off which will dictate the quantity of helium that must be supplied in the field and the
length of time needed between re-fills of the helium reservoir.
Developing the cryostat involved coping with severe design constraints on size and weight, both of
which must be much smaller than for conventional laboratory-grade cryostats. These constraints are
driven by the space and payload capacity of the preferred airborne platform, a Cessna 208. The height
restriction results in unusually short thermal paths between the top plate and the helium reservoir,
which presented a major challenge when designing the structural elements connecting these in a
manner that keeps heat-leaks t to an acceptably low level. In addition, the cryostat must be structurally
much stronger than a typical lab cryostat in order to be certifiably safe to fly, resulting in a relatively
thick structural elements that further exacerbates the difficulty in keeping heat-leaks low enough.
Extensive thermal/structural design work overcame these challenges. As shown in Figure 4 the
cryostat is able to maintain an instrument-space temperature that is stable to less than 0.01 K for
about 27 hours following helium re-fill.
Figure 4. Cryostat thermal performance graph.
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