Peter Shawhan, Andy Lundgren, Nutsinee Kijbunchoo
We did a first -- and successful! -- test of the "detchar" or "safety" hardware injections shortly after 6:00 PDT this morning, at the time recommended by Jeff (work permit 5262).
The detchar injections are a sequence of loud sine-gaussians at a range of frequencies, primarily intended to check for couplings from the GW strain channel to auxiliary channels. (See https://dcc.ligo.org/LIGO-G1500713 .) For now, at least, we are using a set of 14 frequencies logarithmically spaced from 30 Hz to 2000 Hz, each injected at 3 different amplitudes to try to get target SNR values, spaced 5 seconds apart. Here is the full list with times relative to the start time of the injection:
Matlab> GenerateSGSequence('H1','H1_ASD_at_1117710916.txt');
__time__ __freq__ __SNR__ __AMP__
0.50 30.0 25.0 2.22e-20
5.50 41.4 25.0 7.54e-21
10.50 57.2 25.0 2.86e-21
15.50 79.1 25.0 1.72e-21
20.50 109.2 25.0 1.52e-21
25.50 150.9 25.0 1.7e-21
30.50 208.4 25.0 1.97e-21
35.50 287.9 25.0 2.92e-21
40.50 397.7 25.0 3.73e-21
45.50 549.3 25.0 5.42e-21
50.50 758.8 25.0 6.95e-21
55.50 1048.2 25.0 1.1e-20
60.50 1447.9 25.0 1.71e-20
65.50 2000.0 25.0 2.68e-20
70.50 30.0 50.0 4.44e-20
75.50 41.4 50.0 1.51e-20
80.50 57.2 50.0 5.71e-21
85.50 79.1 50.0 3.44e-21
90.50 109.2 50.0 3.03e-21
95.50 150.9 50.0 3.41e-21
100.50 208.4 50.0 3.94e-21
105.50 287.9 50.0 5.85e-21
110.50 397.7 50.0 7.47e-21
115.50 549.3 50.0 1.08e-20
120.50 758.8 50.0 1.39e-20
125.50 1048.2 50.0 2.2e-20
130.50 1447.9 50.0 3.41e-20
135.50 2000.0 30.0 3.22e-20
140.50 30.0 100.0 8.88e-20
145.50 41.4 100.0 3.02e-20
150.50 57.2 100.0 1.14e-20
155.50 79.1 100.0 6.87e-21
160.50 109.2 100.0 6.06e-21
165.50 150.9 100.0 6.81e-21
170.50 208.4 100.0 7.87e-21
175.50 287.9 100.0 1.17e-20
180.50 397.7 100.0 1.49e-20
185.50 549.3 100.0 2.17e-20
190.50 758.8 100.0 2.78e-20
195.50 1048.2 100.0 4.41e-20
200.50 1447.9 75.0 5.12e-20
205.50 2000.0 30.0 3.22e-20
The file, on h1hwinj, is /data/scirun/O1/HardwareInjection/Details/config/Burst/Waveform/detchar_1117890580_3_H1.txt .
With H1 running in good low-noise mode, Nutsinee switched the intent bit to 'commissioning' and we first injected the sequence starting at 1117890580 with an overall scale factor of 0.25 -- so the target SNRs/amplitudes are a factor of 4 smaller than in the table above. Nutsinee didn't see anything obvious appearing in the live spectrum initially, but Andy looked at Omicron output afterward and say that it had picked up at least some of the louder signals.
We then injected the sequence again starting at 1117891250, this time with an overall scale factor of 1.0 . Nutsinee saw the signals clearly peak up in the live spectrogram, and Andy's quick check with Omicron showed many signals found with large SNR. The interferometer appeared to handle the injections fine, staying in lock. Afterward (and also in between the two injections), Nutsinee set the intent bit back to 'science'.
Note: In the future, we expect detchar safety injections such as these to be marked with the DetChar bit in the CAL-INJ_ODC bitmask, but for the test today we treated it as a burst injection -- it will be marked in ODC (and GDS-CALIB_STATE) as a burst injection, and should produce ODC-INJECTION_BURST segments in the DQ segment database.
"Incorrect" sounds too strong to me.
I would say it was incorrect only in the sense that the cavity pole frequency was uncertain which is the case not only for the 24 W configuration but also for the 17 W. Otherwise we believe that the calibration had remained valid both in GDS and CAL-CS at 24 W (though, rememeber CAL-CS has not fully updated to the equivalent of GDS, alog 1880 and hence the descrepancy between them). The OMC has a power-scaling functionality (alog 18470) and therefore, ideally it does not change the optical gain as we change the PSL power. As for the cavity pole frequency, the Pcal lines should be able to tell us how stable it has been.
As reported in alog 18293, the optical gain seemed to have dropped by 4% in this particualr lock according to the Pcal line at 540 Hz. Sudartian is currently analyzing the Pcal trend, but it seems that the optical gain typically changes by 4-5 % in every lock stretch probably due to different OMC error gain (which is computed in every RF->OMC transition) and perhaps different alignment somewhere. We compensated it by increasing OMC-READOUT_ERR_GAIN by 4 % at the beggining of this particular lock and therefore we thought the calibration was good assuming the cavity pole stayed at the same frequency, 355 Hz.
I suspect there is a lingering source of error in the gain of the OMC-DCPD --> DARM_IN1 path. This may be due to the initial gain-matching calculation between DCPD_SUM and RF-DARM, but it could also be due a scaling error as we adjust the overall gain during the power-up step. We initially set the gain at a DARM offset of ~40pm, but as we power up to 23W we reduce the offset to ~15pm. The current gain-scaling calculation that Kiwamu links to does not account for the small static DARM offset that we have observed (it's a fraction of a picometer, see here). I will post a note about this today -- the overall effect should be very small, but may account for the ~4% change that we have observed. (If this is the source of the gain error it will be proportional to DARM offset, which is the same as power level since we change both at the same time.)