Abstract
Hydroxide catalysis bonding has been used in gravitational wave detectors to precisely and securely join components of quasi-monolithic silica suspensions. Plans to operate future detectors at cryogenic temperatures has created the need for a change in the test mass and suspension material. Mono-crystalline sapphire is one candidate material for use at cryogenic temperatures and is being investigated for use in the KAGRA detector. The crystalline structure of sapphire may influence the properties of the hydroxide catalysis bond formed. Here, results are presented of studies of the potential influence of the crystal orientation of sapphire on the shear strength of the hydroxide catalysis bonds formed between sapphire samples. The strength was tested at approximately 8 K; this is the first measurement of the strength of such bonds between sapphire at such reduced temperatures. Our results suggest that all orientation combinations investigated produce bonds of sufficient strength for use in typical mirror suspension designs, with average strengths >23 MPa.
Highlights
A number of interferometric gravitational wave detectors exist around the world
There are a number of these detectors; the LIGO project [2], which operates long baseline (4 km arm length) interferometers at two sites in the US, GEO600 [3], which operates a detector with 600 m arms in Germany, and the Virgo project [4], which operates a detector with 3 km arms in Italy
Bonds created between sapphire surfaces parallel to the c-plane and a-planes of the crystal had an average strength throughout the bond layer of 23 ± 3 MPa at liquid helium temperature and a maximum strength of 42 ± 5 MPa
Summary
A number of interferometric gravitational wave detectors exist around the world. These longbaseline interferometers are designed such that gravitational waves caused by astrophysical events such as the coalescence of binary neutron stars should induce measurable relative displacements of the interferometer mirrors. GEO600 was the first interferometer in which the hydroxide catalysis bonding technique was implemented to create quasi-monolithic suspensions of fused silica to support the interferometer mirrors [6] This bonding technique was first invented for use in the Gravity Probe B project [7] and developed further for gravitational wave detector applications [6, 8, 9]. In order to investigate the strengths of hydroxide catalysis bonds at temperatures reached in a typical cryogenic gravitational wave detector, the bonds were cooled down with liquid helium to approximately 8 K for strength testing.
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