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swinkels - 19:47 Tuesday 04 August 2009 (24071) Print this report
Etalon does not work
More evidence that something strange happened to the apparent finesse of the cavities after the earthquake. Attached figures show the usual etalon plots, plotting B7/B5 and B8/B5 versus mirror temperature according to Michele's drum-mode technique. The etalon is clearly visible thanks to some TCS overdose. The points from after the earthquake do clearly not follow the standard pattern. There is a small possibility that the temperature monitor got crazy (can happen if the drum-modes cross in frequency), but it seems a bit of a coincidence.
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Comments to this report:
punturo - 11:08 Wednesday 05 August 2009 (24085) Print this report
The small worry expressed by Bas about the reliability of the mirror temperature monitor is not confirmed. The moniitor seems to work well and any swap between the mirror modes is occurred. This is suggested by the fact that both the drum mode and the butterfly modes show the same behavior (a simultaneus mode swap is really improbable). The monitor has been recently improved:
1) all the drum and butterfly modes are detected, but the "WE" drum mode that seems noisy
2) finally, the temperature trend plots are automatically generated and plotted at the address: http://wwwcascina.virgo.infn.it/commissioning/MirrorT/.

The discrepancy between the power transmitted at the end of the arms and the etalon prediction has been well explained during VSR1 by the end benches misalignment, as described in the entries:
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