We tried to perform the noise projection from IMMT1 trans QPD to DARM.
1. Shaking the MCo
In klog32583, they measured the transfer function from IMMT1 TRANS QPD1,2 P,Y by shaking the MCo suspension.
I tried to project it to current DARM sensitivity.
Fig.1. showed the one result.
Red : current sensitivity curve
Green : IMMT1 TRANS QPDA1,2 PIT,YAW with IMC output power 1.2 W
Blue : IMMT1 TRANS QPDA1,2 PIT, YAW with IMC output power 10 W
Even in case of the projection using 10 W spectrum, we evaluated too overestimate, that implied the larger noise path exist compared from beam jitter when we fluctuated the MCo.
Maybe, beam jitter can be produced by fluctuating the MCo, but other fluctuation also induced, such as intensity noise, frequency noise and so on, and their effect to DARM would be larger than beam jitter one.
2. Using the previous result of the shaker injection
in klog32007, we also evaluated the transfer function from IMMT1 TRANS QPD2 PIT,YAW to DARM by oscillating the floor by large shaker.
By applying this transfer function to IMMT1 TRANS QPD2 PIT,YAW with 10 W operation, we can obtained the Fig.2.
Still overestimate can be seen in the results, the shape close to the DARM sensitivity.
We need to measure the TF using several shakers later.
As the frequency range of the TF measured with the shaker injection was from 75Hz to 150Hz (fig001), what we can know is the information in this freq range.
What is the difference with the result 2 years ago (see https://klog.icrr.u-tokyo.ac.jp/osl/?r=24187)?
I projected intensity and frequency noise at the time of the transfer function measurement in to DARM with transfer functions I found in the Noisebudget TFs folder /kagra/Dropbox/Measurements/NoiseBudget/TFs/2023/0621/ : CARM2DARM_202306211610.xml and ISS2DARM_202306211610.xml. Frequency noise produced by MCO drive and coupled in to DARM is of the correct order of magnitude to explain the observed coupling to DARM. The shape however is not correct. Could CARM loop or CARM coupling have achanged since June 2023.
Comparing the two transfer function measurements, they are very similar (first 2 attachements). With 1E4 amd 2E4(old) at 100Hz in uncalibrated units. The passive transfer function (attached) would indicate coupling of about 2E3 in pitch at ~100Hz in uncalibrated units (where there is high coherence) and similarly off by a factor 10 at ~200Hz. The excitation amplitude in the old xml file is 10000 counts while the more recent drive was 500 counts at essentially the same excitation point for the transfer function measurements, but that seems to have had little effect. That would leave only the Jittter and DARM noise amplitudes as the variables between the two klogs.
