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.
Calculation of thermal noise in grating reflectors Heinert, D.; Kroker, S.; Friedrich, D. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
08/2013, Letnik:
88, Številka:
4
Journal Article
Odprti dostop
Grating reflectors have been repeatedly discussed to improve the noise performance of metrological applications due to the reduction or absence of any coating material. So far, however, no ...quantitative estimate on the thermal noise of these reflective structures exists. In this work we present a theoretical calculation of a grating reflector's noise. We further apply it to a proposed third generation gravitational wave detector. Depending on the grating geometry, the grating material, and the temperature, we obtain a thermal noise decrease by up to a factor of 10 compared to conventional dielectric mirrors. Thus the use of grating reflectors can substantially improve the noise performance in metrological applications.
Mechanical losses of crystalline silicon and calcium fluoride have been analyzed in the temperature range from 5 to 300 K by our novel mechanical spectroscopy method, cryogenic resonant acoustic ...spectroscopy of bulk materials (CRA spectrocopy). The focus lies on the interpretation of the measured data according to phonon-phonon interactions and defect induced losses in consideration of the excited mode shape.
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