Jennie W, Robert S, Sheila, Camilla, Georgia

We are worried about jitter peaks in DARM and input pointing just now so Camilla and Sheila asked me to look at the PEM accelerometer we have on the main periscope in the PSL.

The first image is a time series of periscope acceleration on the top, lock state in the middle and range on the bottom. The first vertical cursor shows a time when we were locked at NLN before the vent on 1st April, and the second is during a quiet time with no squeezing injected that Camilla and co. were using for squeeze measurements yesterday 4th June. One can see that the rms motion increased from around 670 counts before the vent to around 1200 after the vent.

The second image shows the spectra of the accelerometer on the top left plot, the darm spectra on the bottom left, and the coherence from accelerometer to darm on the top right plot - plotted for both times.

Ref 0 periscope asd now

ref 1 periscope asd pre-vent

ref 2 darm asd pre-vent

ref 3 periscope to darm coherence pre-vent

ref 4 periscope to darm coherence post-vent

ref 5 darm asd post-vent

After looking over these with Robert, he thinks that the jitter is not much higher up to about 200 Hz but noticeably worse between 500 Hz and 1kHz. There have been vacuum pumps attached to HAM1 post-vent, but these would not cause the broadband features we can see in this region and would instead be reponsible for narrow peaks.

He wants to check the air handling in the PSL enclosure to rule this out as a source.

Since the coherence with DARM is not big for these peaks this will not be causing our jitter problems currently.