RUI: Ultracryogenic Acoustic and Thermal Evaluation of Metals for Gravity Wave Detectors

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Professor Duffy will continue ultracryogenic studies of the mechanical quality factor (Q) of selected polycrystalline technical materials. The quality factor will be measured on torsional resonators machined in the unique configuration developed by him. The configuration permits audio frequency measurement (typically at 1 kHz) over a wide range of Qs (103 - 108) and a wide range of temperatures (50mK - 300K). Since only a small piece of material is involved (typically 6 cm diameter by 6 cm long), the cost of operation and the turn-around time of the complex dilution refrigerator cryostat needed for the very low temperature measurements are kept low. The work is to be carried out in support of cryogenic (4K) and ultracryogenic (100 mK) resonant mass gravity wave antenna development both in the United States and abroad. Close contact will be maintained with the gravity-wave- detector community. Materials to be studied include those which offer the most promise for use as gravitational wave detectors of high sensitivity. This requires materials of high Q, which also have appropriate inertial, elastic and thermal properties. Specific materials which are the focus of this study include an explosively bonded aluminum alloy 5056 and a series of copper and aluminum alloys. Grain size and hardness will be evaluated. Appropriate heat treatments will be developed, which have been found to be so essential for obtaining high ultracryogenic Qs in the materials studied to date. Ultralow temperature heat capacity and thermal conductivity studies of selected materials will be carried out. In addition to supporting gravity wave antenna development, the results should contribute to the fundamental understanding of acoustic loss mechanisms.