daniel.vander-hyde@LIGO.ORG - posted 21:06, Friday 11 January 2019 - last comment - 22:10, Friday 11 January 2019(46382)
ISS second loop coupling into DARM
Sheila, Danny
We wanted to investigate the 380-410 Hz peaks in DARM noted by Robert in alog 46373
Sheila noticed that there was a strong coherence between the seismometers and the ISS in loop diodes around these same frequencies which lead us to discover the strong coherence of the ISS in loop diodes and DARM.
We do not notice this noise in DARM when the ISS second loop is off.
When the second loop is engaged there doesn't seem to be an agreement between the out of loop sensors for this . The HAM2 ISS out of loop diodes show that there is noise suppression in this range while the HAM1 REFL diodes show that there is added noise.
We also note that there was a strong coherence below 30 Hz between the in loop diodes and DARM when the ISS is AC coupled.
Further investigations coming soon
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daniel.sigg@LIGO.ORG - 22:10, Friday 11 January 2019 (46383)