This week, we tested the damping components recently added on ISI-BSC8. These components are:
-          The vibration absorbers on stage 1
-          The Tuned mass dampers on the blades that go from stage 0 to stage 1
-          The Viton pads under the stack mass on top of stage 2

Links to plots are at the end of the aLOG.

Vibration Absorbers (217Hz resonance)
We performed test with different thicknesses of Vitton Pads with and without the lids. These configurations (S=0.25”x0.25”) are:
- Thickness: 0.0625”, 0.125”, 0.25” without lid
- Thickness: 0.0625” with lids and pads of 0.0625” and 0.125”

The best configuration:
- Bottom pads with a thickness of 0.0625”
- The top pads thickness doesn’t seem to affect the performance.

Performance on the 217Hz resonance (the only resonance affected by the vibration absorbers):
- X, Y directions reduction by a factor of 7.4 on ST1 L4C
- RX, RY directions reduction by a factor of 7 on ST1 L4C
- the resonance is not visible on GS13

TMDs on Blades 0-1 (252 Hz resonance)
HAM-ISI TMDs were retuned at 252Hz for BSC-ISI stage 0-1 blades. Details are given in E1100963-v1. The TMDs (base) are installed at 11 inches from the post.

Performance on the 252Hz resonance (mainly visible on X, Y, RX)
- Direction X: 252 Hz resonance not visible and the new resonances created by the TMDs are not visible
- Direction Y: 252 Hz resonance not visible. One of the new resonances is at 238 Hz and 5 times lower (Corner 2 is the main contributor of the resonance in the Y direction). The amplitude reduction in corner 2 is similar to those observed in the other corners. (TF in the local basis).
- Direction RX: 252 Hz resonance not visible and the new resonances created by the TMDs are not visible

Viton pads (1"x1"x0.25") under the stack of masses on top of stage 2
- Effective on resonances at 162Hz, 180Hz and 227Hz. Measurements stop at 500Hz. More measurements are coming for higher frequencies.

Next Step:
- Full set of transfer functions (10mHz to 1KHz)
- TFs evolution with the payload (to evaluate stage 2 new resonances created by SUS)

The plots:
2012 01 06: No TMD - No vibration absorbers - No Viton pads
2012 01 25: TMDs - 3x 2 vibration absorbers (Bottom pads - 0.0625" - top pads 0.125") - Viton pads (1"x1"x0.25") 8 per stack
https://svn.ligo.caltech.edu/svn/seismic/BSC-ISI/H2/ITMY/Data/Figures/Transfer_Functions/
Comparisons/
LHO_ISI_BSC8_Comparison_TF_C2C_ST1_ACT_H_to_ST1_L4C_H_20120106_vs_20120125.fig
LHO_ISI_BSC8_Comparison_TF_C2C_ST1_ACT_V_to_ST1_L4C_V_20120106_vs_20120125.fig
LHO_ISI_BSC8_Comparison_TF_C2C_ST2_ACT_H_to_ST2_GS13_H_20120106_vs_20120125.fig
LHO_ISI_BSC8_Comparison_TF_C2C_ST2_ACT_V_to_ST2_GS13_V_20120106_vs_20120125.fig
LHO_ISI_BSC8_Comparison_TF_L2L_ST1_ACT_H_to_ST1_L4C_H_20111206_vs_20120125.fig