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MIF (General)
adam.mullavey - 17:04 Friday 06 December 2019 (11971) Print this report
DARM needs a boost

Sheila, Adam,

We were curious about the DARM residual and how much of the linear range of the error signal it is using in a typical lock. I found a DQ'd channel that looks like the calibrated residual, K1:CAL-CS_PROC_DARM_RESIDUAL_DBL_DQ. The attached plots show the spectrum and rms of this residual from Tuesday night (see The DARM sensitivity (GW channel) is also included.

As one can see the RMS of the residual is 4x10-11 m, which is approximately 1/4th of the peak of the error signal (which is at the cavity pole 16Hz). I realize I'm comparing metres to Hz, so here is the calculation.

vres = vlaser * Lres / Larm

vres = 3x1014Hz * 4x10-11m / 3x103m

vres = 4 Hz

This seems quite large, so we think we should boost the DARM loop to suppress this more.

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sheila.dwyer - 22:06 Friday 06 December 2019 (11982) Print this report

Masayuki, Keiko, Adam, Sheila

We engaged the darm boost shown in the first attachment, and to recover some phase turned off the 1.48Hz lag filter in ETMY ISCINF, as well as the 60 Hz comb filter. Masayuki added a guarian state called DARM_BOOST which will engage this in the future. 

Engaging this filter reduced the DARM residual RMS from 3e-11 meters to 2e-12 meters.  The AS camera also became more stable, and the width of several lines in the DARM spectrum were reduced.  The second attachment shows a couple of on/off tests, there are several things in the spectrum that are changing independent of the DARM boost but it does seem that the sidebands on the 60Hz lines are reduced, the 180Hz, 200 Hz and 300Hz peaks seem to go away.  The broadband noise from 10-30Hz also seems lower with the boost on.

After we egaged the boost, Keiko and Masayuki turned on the MICH ASC and moved ETMY alignment, after this the AS camera really looks like a dark port. Adam recoreded a video of the much calmer AS port, I can't attach it to the alog but it is as users/adam.mullavey/ASportdarmboosted

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masayuki.nakano - 22:30 Friday 06 December 2019 (11984) Print this report

High frequency sensitivity got better by factor of 5!!

Because of the contrast defect, the frequency noise, the intensity noise, or other common noise coupling was large. After tweaking of the alignment, the high frequency noise got much better.
Also, since the DARM error signal RMS got small, I could engaged the whitening stage of AS PD. It improved the sensivity factor of 2 more.

The BNS inspiral range is above 10 kpc now.

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takashi.uchiyama - 22:34 Friday 06 December 2019 (11985) Print this report
Wow, wow, wow!!!

Thank you
tomotada.akutsu - 0:25 Saturday 07 December 2019 (11988) Print this report


Well, that might be consistent with that some ASC measurements shaking the test masses at lower freq region cause varying the sensitivity of the interferometer at higher freq region, as discussed in the afternoon meeting.

tomotada.akutsu - 1:16 Saturday 07 December 2019 (11989) Print this report

Now it is reaching order of 1e-17m/rtHz around 10-1kHz, it might be nice to consider couplings from RF noises (both phase and amplitude), as we still are using RF modulation to lock the FPMI. Putting my master thesis here (written in Japanese using an ancient interferometer) is very embarrassed for me, but hopefully it might be useful. (for example, Fig 6.10)

takaaki.yokozawa - 8:14 Saturday 07 December 2019 (11990) Print this report

Thank you for your great effort! I will check the coherence soon.

I would like to leave the memo. After FPMI lock, BS Yaw started the oscillation with 0.18Hz(even I applied the sallignment).

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tomotada.akutsu - 9:50 Saturday 07 December 2019 (11991) Print this report

By the way, looking at the spectrum of the BS oplev that Yokozawa-san attached, I wonder that the wind-shielding of the oplev setup would not be sufficient...?? or something wrong... The slope in the lower freq region seems too artificial??

tomotada.akutsu - 23:01 Tuesday 17 December 2019 (12195) Print this report


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