Technical Design Document of the fibre guard in the aLIGO ETM/ITM quad suspension

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Abstract:: The quasi-monolithic suspension of the ETM/ITM mirror from the penultimate mass is the final stage in the quadruple suspensions in aLIGO. The stage is constructed entirely of fused silica with interface pieces or ‘ears’ bonded to the sides of both the penultimate mass and the test mass and 4 silica fibres welded in between the horns on the ears to connect the two together. The final stage is one of the more valuable parts of the quad suspension in the monetary sense, but also from a performance point of view and technological point of view. The thermal noise performance of this suspension has to meet some challenging requirements, and the technologically advanced method of welding in fused silica fibres, means that this stage should be handled with great care. Several safety features are in place like bumper stops that limit the motion of the penultimate mass and test mass to only a few millimeters in any direction, and fibre guards in between the masses that protect the fibres from human interference.
This document discusses the motivation and requirements for the fibre guards, gives a description of their design and gives some key notes on installation into the structure.

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Keywords:: aLIGO suspensions quad suspension monolithic suspension ETM/ITM structure fibre guard

LIGO Document T1000472-v1