LIGO Document T0900509-v1

Gas Damping of the Final Stage in the Advanced LIGO Suspensions

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T - Technical notes
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The finding by the Trento group (Cavalleri 1 (2009), Cavalleri 2 (2009)) of increased gas damping in a torsion oscillator when moving in a constrained volume and the subsequent application of this finding to the Advanced LIGO suspension (Robertson and Hough (2009)) are analyzed in this note. The damping from the residual gas has been re-estimated from first principles for the Advanced LIGO suspension geometry and outgassing by the surfaces has been included.

The damping is not as large as estimated by Robertson and Hough but is not a negligible component of the Advanced LIGO noise budget.

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gas vacuum suspension
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