Viton pads are usually set under the balancing masses of the HAM-ISIs in order to damp resonances at high frequencies (above 100Hz).
The SEI team would like to asses the improvements that the Viton Pads help achieving. To do so, we decided to have viton pads under the balancing masses of the ISIs of LLO's IMC, and to try without those pads here at LHO.
Transfer functions were measured ovenight on LHO HAM3-ISI. We compared those transfer functions with the ones measured at LLO under an equivalent state:
- ISI is in vacuum
- MC2/PR2 are installed and damped
- TMDs are intalled on the ISI
- HEPI is locked
Comparative plots are attached.
The script which produced the plots mentioned above was re-checked. The curves it displays match with the ouput of the generic commissioning scripts, for both LLO and LHO.
Data in the 5Hz-200Hz range was retreived and added to the plot. Results are attached.
The results presented above were calibrated and transposed into the cartesian Basis, as performed during the step 3 of the commissioning process of HAM-ISIs.
Narrow peaks can still be seen on LLO's transfer functions. We held off on the installation of the Scraper Baffles here, while they were already on the ISI at LLO, at the time of the measurement. It could be the cause of it.
Once HAM3 chamber is open, we will look at the items installed on the ISI. It should help clarifying the cause those peaks that we did not witness here.
I attached a picture of HAM3 chamber taken on Dec 6th 2012. Pumpdown started on Dec. 21st.