Low mechanical loss materials are needed to further decrease thermal noise in upcoming gravitational wave detectors. We present an analysis of the contribution of Akhieser and thermoelastic damping ...on the experimental results of resonant mechanical loss measurements. The combination of both processes allows the fit of the experimental data of quartz in the low temperature region (10K to 25K). A fully anisotropic numerical calculation over a wide temperature range (10K to 300 K) reveals, that thermoelastic damping is not a dominant noise source in bulk silicon samples. The anisotropic numerical calculation is sucessfully applied to the estimate of thermoelastic noise of an advanced LIGO sized silicon test mass.
Future generations of gravitational wave interferometers are likely to be operated at cryogenic temperatures because one of the sensitivity limiting factors of the present generation is the thermal ...noise of end mirrors and beam splitters that occurs in the optical substrates as well as in the dielectric coatings. A possible method for minimizing thermal noise is cooling to cryogenic temperatures, maximizing the mechanical quality factor Q, and maximizing the eigenfrequencies of the substrate. We present experimental details of a new cryogenic apparatus that is suitable for the measurement of the temperature-dependent Q-factor of reflective, transmissive as well as nano-structured grating optics down to 5 K. In particular, the SQUID-based and the optical interferometric approaches to the measurement of the amplitude of vibrating test bodies are compared and the method of ring-down recording is described.
Upcoming generations of interferometric gravitational wave detectors are likely to be operated at cryogenic temperatures because one of the sensitivity limiting factors of the present generation is ...the thermal noise of optical components (e.g. end mirrors, cavity couplers, beam splitters). The main contributions to this noise are due to the substrate, the optical coating, and the suspension. The thermal noise can be reduced by cooling to cryogenic temperatures. In addition the overall mechanical quality factor should preferable increase at low temperatures. The experimental details of a new cryogenic apparatus for investigations of the temperature dependency of the Q-factor of several substrate materials in the range of 5 to 300 K are presented. To perform a ring down recording an electrostatic mode excitation of the samples and an interferometric read-out of the amplitude of the vibrations was used.
In this paper, we introduce a new kind of two-stage pulse tube refrigerators. The chosen entire coaxial configuration combines the advantages of the coaxial design with the two-stage pulse tube ...concept. Lead coated screens build the inhomogeneous regenerator matrix of the second stage. Without any rare earth compounds the refrigerator reaches a no load temperature of 6.6
K at the second stage cold tip. The active type of phase shifting is generated by a rotary valve combined with two needle valves at the hot end of each pulse tube (compressor Leybold RW 6000, 6
kW input power). This paper focuses on the design parameters and first performance measurements.
Fundamental mechanical loss mechanisms exist even in very pure materials, for instance, due to the interactions of excited acoustic waves with thermal phonons. A reduction of these losses in a ...certain frequency range is desired in high precision instruments like gravitational wave detectors. Systematic analyses of the mechanical losses in those low loss materials are essential for this aim, performed in a highly sensitive experimental set-up. Our novel method of mechanical spectroscopy, cryogenic resonant acoustic spectroscopy of bulk materials (CRA spectroscopy), is well suited to systematically determine losses at the resonant frequencies of the samples of less than 10-9 in the wide temperature range from 5 to 300 K. A high precision set-up in a specially built cryostat allows contactless excitation and readout of the oscillations of the sample. The experimental set-up and measuring procedure are described. Limitations to our experiment due to external loss mechanisms are analysed. The influence of the suspension system as well as the sample preparation is explained.
We have developed a lead-based regenerator material which is suitable for working temperatures below 20 K. This material can be used as a substitute for the state of the art non-magnetic materials ...used today within very low-temperature regenerators. This high efficient regenerator matrix combines technological advantages with the possibility to vary the thermodynamic and flow characteristics over a wide range, continuously. Hence, our self-made electroplated screen material is compared with standard regenerator materials (commercially available woven screens and packed spheres). We present the pressure drop and heat transfer characteristics of the new material for matrix porosities between 0.55 and 0.38 which corresponds to the porosities of screens and packed spheres. The design parameters and the influencing variables to optimise the regenerator performance will be discussed. The utility of the shop-made lead coated regenerator material is demonstrated in a coaxial two-staged pulse tube refrigerator with working temperatures below 6 K.
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