R&D (FilterCavity)
DaisukeTatsumi - 10:04, Saturday 19 November 2016 (330)
Failure of BS suspension wire setting

Worker: Yuefan Guo, Daisuke TATSUMI

We failed to set suspension wire of BS mirror.

We try three times and always break the suspesion wire during the pulling up

the aluminum dummy mirror.

I guess that these failure come from systematic reasons.

Therefore, we stop the work today.

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I know the safy factor of tensile strength is about 2 for 10cm fused silica mirror.

Because BS mirror has different dimensions, I calculate several parameters.

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1) Tensile strength of tungsten wires
2500-3500 N/mm^2
 
2) Wire dimensions
Diameter           50 micro-meter
Number of wires    4
 
-->
2500 N/mm^2 * (0.025 * 0.025 * pi) * 4
= 19.6 N
= 2.0 kgf
 
 
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3) Mass of mirror and dummy
 
Diameter 1 0cm / Thickness 6 cm     Volume = 471 cm^3
Diameter 15 cm / Thickness 4 cm     Volume = 707 cm^3
 
Density of
Fused silica           2.20 g/cm^3
Aluminum alloy 5052    2.68 g/cm^3
 
Weight of
10cm / Fused silica    1036 g
10cm / Aluminum        1262 g
 
15cm / Fused silica    1555 g
15cm / Aluminum        1895 g
 

It means that for 15cm alumimum dummy mirror,

there is almost no safety factor. If tension balance of four wires is not good,

the wires will break easily.

I decide to change the wire diameter to 100 micron.

P.S.

High wire tensions are needed to reduce its mechanical loss.

For stearing mirror of the filter cavity, we do not take car of thermal noises.