AAWSAP DIRD, High-Frequency Gravitational Wave Communications, April 2010

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disadvantage that this device is of a unique design that is currently available only from
Yale University, and is likely not to be exportable. This task will include developing a
conceptual design using this alternative type of receiver for the PPF arising from
HFRGW.
DD1.6 Cryogenic System
Specification and design of the cryogenic system refrigeration unit, required for low­
temperature operation to obtain the best possible reduction in intrinsic thermal noise:
Dr. R.C. Woods (LSU) + graduate student, Dr. R. M L Baker (TSC), G.V.
Stephenson (TSC). The required criterion is that the temperature T satisfies kBT < <
nw (where kB is Boltzmann's constant); that is, T << nw/kB ~ 480mK for detection at
10GHz. This condition is satisfied by the target temperature for the interaction volume
T < 48mK, which can be obtained using a common helium-dilution refrigerator. Then,
the signal PPF will be significantly greater than the thermal photon flux.
Cost/performance tradeoffs may also be important in this design, so that other possible
economic solutions to receiver cooling will also be considered before finalizing the
design.
DDl.6.1 Off-the-shelf cryogenic systems: a number of companies have developed
ultra-low temperature systems (mK range) for a variety of applications. A common
application is refrigeration of receivers as needed in the Li-Baker HFRGW detector. One
possibility is the Oxford Instruments' KelvinoxMX range (see summary data attached)
that appears to suit the present requirements subject to further evaluation of each
model in the range. Other manufacturers to be investigated include Scientific Magnetics
(UK), and Cryofab Inc. (Kenilworth, New Jersey).
DDl.6.2 Specifications for system best suited to the detector: specifications will
be established for the selected cryogenic system. This will include cryogen level
monitoring devices (for example, Oxford Instruments Intelligent Level Meter ILM200)
for warning if the cooling fails.
DD1.7 Electromagnet
Development of the electromagnet specification needed to produce the required static
magnetic field (up to 35T, ~3T nominal): Or. R.C. Woods (LSU) + graduate
student, Dr. R. M L Baker (TSC), G.V. Stephenson (TSC). It is expected that a
commercial design can be identified for this task. The chosen design will be capable of
providing the requisite magnetic field at least over the interaction cavity volume in the
containment vessel. Exceptional field-uniformity is not a particularly important issue in
this application, though the GW interaction volume or cavity (roughly cylindrical, 6cm
diameter and 30cm long) plus extra volume for the surrounding apparatus is somewhat
larger than many other experimental applications require, and the required field is
perpendicular to the cylindrical axis. Hence, one solution is that the final solenoid
design must completely surround the cylindrical axis of the interaction volume
perpendicular to the applied field. An alternative approach is to use two solenoids, one
each side of the interaction volume, similar to the popular Helmholtz coil configuration.
In a development of this, a number of small ( ~6cm diameter) solenoids could be
stacked along the length of the interaction volume, with their Helmholtz-like opposite
paired solenoids the other side of the interaction volume. In the latter cases, since the
paired solenoids are not perfect ring coils, the resultant field would be non-uniform. A
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