KAGRA Logbook

MIF (ASC)

takafumi.ushiba - 22:57 Sunday 12 February 2023 (23933)

Test of arm ADS with PRFPMI

[Yamamoto, Ushiba]

Abstract:
Arm ADSs with PRFPMI configuration were tested.
We engaged ADSs to both ETMs but not succeeded.
We need more time to complete arm ADSs.

Detail:
We started to test ADSs for arm with PRFPMI configuration.
Followings are the configuration, which we tested.

* Lock PRFPMI without DC readout (LSC guardian state is PRFPMI_RF_LOCKED).
* Excite pitch and yaw of ETMs from ETM DOF{1,2} oscillators.
* Excitation freqwuency is 5.4 (ETMY pitch), 5.7 (ETMY yaw), 6.3 (ETMX pitch), and 6.6 (ETMY yaw) Hz.
*Amplitude is 300 cnts for pitch and 100 cnts for yaw.

Once ADSs are turned on, alignment seems gradually better and normalized transmitted light power for both arm can reach 130.
However, both pitch ADSs continue to drift even after reaching good alignment, and alignment becomes bad soon.
I felt there is some offset on error signals of ADSs but cannot find the source of the offset today.
We need more time to engage ADSs stably.

Comments to this report:

takaaki.yokozawa - 9:44 Monday 13 February 2023 (23939)

I checked the spectrum of POP 90 I

Images attached to this comment

23939_1676249048_Screenshot from 2023-02-13 09-40-27.png

masayuki.nakano - 11:36 Monday 13 February 2023 (23940)

This is exactly what I've experienced in the O3GK commissioning.

One possibility is as follows:
Dithering causes the length fluctuation as well if the beam is not centered. As far as the DARM loop is fast enough, and the DARM offset is zero, it won't matter since the length fluctuation will be well suppressed and the intra-cavity power is quadratic for the length motion. But otherwise, the length dither makes the power modulation, and this can be the offset of the error signal. We have DARM offset for DC readout, and also, the DARM loop is kinda slow. So, the DARM suppression might not enough at the dither frequency. You can try to reduce the dither frequency. Or beam centering loop might help, but not work for ITMY.