Measurements of the mechanical quality factor Q in a single crystal of silicon vs. temperature have been made. A value of 2x lO 9 has been measured at T=3.5K.We have been studying large dielectric and semiconductor single crystals as possible gravitational wave detectors. 1 These detectors are frequently cylinders instrumented to detect vibrations of the first longitudinal mode. One of the important desirable properties is a high mechanical quality factor Q. With an ideal transducer the sensitivity to gravitational waves is proportional to Q. The inverse quality factor Q-1 is a direct measure of the dominant mechanism of the attenuation of first sound. Measurements of Q are frequently the best way to gather information concerning the various internal loss mechanisms of a substance. In the region of very high Q (low loss) this sometimes is the only easy method. We report here on measurements on a large single crystal of silicon whose Q values exceed 10 9.The crystal was manufactured by Monsanto by the zero-dislocation Czochralski process in the form of a cylinder (diameter 10.6 cm, length 22.9 cm, mass 4.9 kg), with the [111] axis parallel to the cylinder axis. The ends were polished by the University of Rochester Institute of Optics personnel to better than one wavelength of light. The barrel of the crystal, somewhat wavy from the crystal growing process, was left in this state so that its edge deviates from straightness by -1 mm. The crystal is a p-type

Direct drive laser fusion ignition experiments rely on detailed understanding and control of irradiation uniformity, the Rayleigh-Taylor instability and target fabrication. The Laboratory for Laser Energetics (LLE) is investigating various theoretical aspects of a direct drive National Ignition Facility (NIF) ignition target based on an 'all-DT' design: a spherical target of ∼3.4 mm diameter, with a 1-2 µm CH wall thickness and a DT ice layer of ∼340 µm near the triple point of DT (∼19 K). OMEGA experiments are designed to address the critical issues related to direct drive laser fusion and to provide the necessary data to validate the predictive capability of LLE computer codes. The cryogenic targets to be used on OMEGA are hydrodynamically equivalent to those planned for the NIF. The current experimental studies on OMEGA address the essential components of direct drive laser fusion: irradiation uniformity and laser imprinting, Rayleigh-Taylor growth and saturation, compressed core performance and shell-fuel mixing, laser-plasma interactions and their effect on target performance, and cryogenic target fabrication and handling.

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