Lisa, Evan
Attached is a spectrum of the suppressed DARM error signal from last night. The RMS is about 3×10−13 m down to 0.1 Hz, and (as we've already seen) almost all of it comes from motion between 1 and 5 Hz. By looking at the recent DARM OLTF for H1 (LHO#17153), we see that we easily have more room for a boost below 10 Hz or so (and Dan is already working on this).
Also attached are spectra of recent "best" locks from H1 and L1, along with the GWINC prediction for 10 W of input power.
P.S.: The rms traces of the calibrated DARM signals in DTT appear to be completely bogus. The attached plot was done independently in python.
P.P.S.: Attempting to print these spectra in pdf, eps, or ps causes DTT to crash.
Some plots with the best L1 and H1 sensitivity curves so far.
The attached image describes the effect of the boost filter we'd like to add to DARM. The blue trace is the current set of DARM integrators, boosts, RGs, and so on (I haven't included the suscomp filter). The red trace has the new boost in FM7. The blue trace is the same as the comparison that Peter made between H1 and L1 back in February. Compare the red trace in the attached plot (the change we'd like to make) to the L1 trace in his comparison; this boost will bring us more in line with the Livingston loop shape. (The changes made two weeks ago to the DARM loop were made to the suscomp filter.)
The boost adds 20dB of gain at 3Hz, takes away ~1.5dB at 10Hz due to a pair of complex zeroes, and loses about 4deg of phase at 50Hz. The last DARM OLTF we measured says we have 45deg of phase margin at the 50Hz UGF, and probably about 30dB of gain at 3Hz, so this filter should significantly improve the suppression in the 2-5Hz band without costing too much phase.
We might want to add an RG filter at 0.45Hz to suppress the pendulum resonance, too. Or increase the existing RG in FM3.
