J. Kissel, T. Shaffer, J. Warner

In prep for all modifications to the H1CALEY PCAL Periscope structure (camera relay mirror removal, vibration absorber install, baffle panel install), Jim, TJ, and I measured the response of the PCAL periscope as it had been for all of O1 and O2, and compared it against LLO's recent results, trying to repeat their study as closely as possible (see LLO aLOG 33697).

The results are strikingly (haaaaaaa!) similar. See main attached "H1vsL1" .pdf for comparison between the most coherent measurement (striking in the three o'clock position, close to the inner annulus, with the accelerometer just below it). Prominant features (for both) are at ~67, 106, 115, and 210 Hz.

Because the response is so similar to LLO's periscope, it gives us high confidence that the vibration absorber installation plan (E1700125) will work nicely. As such, we'll not bother taking the full gamut of piece-by-piece removal and installation of parts, and just take the measurement again after all modifications are complete.

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Details
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Measurement repeat:
- We installed B&K accelerometer mounting plates in two locations ("12 O'Clock" and "3 O'Clock"), as shown in the first picture attachment.
- We measured the response in these two locations, moving the accelerometer from location to location, but hitting the hammer in the same location for each measurement. The remaining pictures show further detail.
- The accelerometer is mounted with its X axis aligned with the IFO's global Y direction, i.e. Longitudinal of ETMY in the IFO laser beam direction. Accelerometer Y is anti-aligned with IFO X, and Z is pointing toward the ground, anti-aligned with local gravity. The hit direction is with the IFO's Y axis, the accelerometer's X axis, and the beam direction, exciting drumhead modes of the periscope.

- The first .pdf shows a comparison between H1 and L1 persicope, both prior to any mirror removal, vibration absorber install, or baffle install.
- The second attachment shows all three DOFs of both measurement locations in case they're needed. The L1 data is identical to what is shown in LLO aLOG 33697, namely,
    /ligo/svncommon/SusSVN/sus/trunk/QUAD/L1/ETMY/BandK/
        SimpleHammerDisplay3-ETMY-PCALBaffleYT1a-SUSunlocked-ISIunlocked-VAnotfitted-Ximpact.txt (12 O'Clock response)
        SimpleHammerDisplay3-ETMY-PCALBaffleYT2a-SUSunlocked-ISIunlocked-VAnotfitted-Ximpact.txt (3 O'Clock response)