Yesterday, the first set of transfer functions on ISI-BSC8 was measured in vacuum. Here are the links to a comparison with the previous measurements in air. TFs are presented in Cartesian basis.

https://svn.ligo.caltech.edu/svn/seismic/BSC-ISI/H2/ITMY/Data/Figures/Transfer_Functions/Comparisons/C2C/

-          LHO_ISI_BSC8_Comparison_TF_C2C_ST1_ACT_H_to_ST1_CPS_H_20120203_vs_20120227.fig

-          LHO_ISI_BSC8_Comparison_TF_C2C_ST1_ACT_H_to_ST1_L4C_H_20120203_vs_20120227.fig

-          LHO_ISI_BSC8_Comparison_TF_C2C_ST1_ACT_V_to_ST1_CPS_V_20120203_vs_20120227.fig

-          LHO_ISI_BSC8_Comparison_TF_C2C_ST1_ACT_V_to_ST1_L4C_V_20120203_vs_20120227.fig

-          LHO_ISI_BSC8_Comparison_TF_C2C_ST2_ACT_H_to_ST2_CPS_H_20120203_vs_20120227.fig

-          LHO_ISI_BSC8_Comparison_TF_C2C_ST2_ACT_H_to_ST2_GS13_H_20120203_vs_20120227.fig

-          LHO_ISI_BSC8_Comparison_TF_C2C_ST2_ACT_V_to_ST2_CPS_V_20120203_vs_20120227.fig

-          LHO_ISI_BSC8_Comparison_TF_C2C_ST2_ACT_V_to_ST2_GS13_V_20120203_vs_20120227.fig

Main differences on main couplings:

-          ST1 ACT to ST1 CPS: HEPI in different state for the two measurements (Locked vs Unlocked) => Resonances between 7 and 60Hz

-          ST1 ACT to ST1 L4C: No difference between the 2 measurements

-          ST2 ACT to ST2 CPS: No difference between the 2 measurements

-          ST2 ACT to ST2 GS13: Some Qs at high frequencies slightly higher in vacuum than in air (resolution may need to be changed at HF)

Tonight, the section 700mHz to 10Hz will be re measured with a better resolution. The goal is to get a nice measurement in order to calculate all the filters (Symmetrization, blend, damping and isolation) using one unique set of measurements.