KAGRA Logbook

IOO (General)

shinji.miyoki - 7:28 Monday 01 September 2025 (34970)

Some observation on IMC Unlock and Relock

IMC showed unlock and successive failure of relock around 5:30. I easily noticed that BOOST in the IMC LOCK GUARDIAN failed every time.

So I manually requested DOWN, GRAB_RESONANCE, DOWN, BOOST, and IMC_Locked, then checked several signal situations. Consequently, IMC could be relocked soon.

Fig.1 shows each signal during "GRAB_RESONANCE, DOWN, BOOST, and IMC_Locked". SERVO_SLOW(PZT path) showed signals around zero. Then the IMC lock was recovered. The two dashed lines in SERVO_NPRO_TEMP show the difference between the relock of IMC and the repeating time of relock and unlock.

Fig.2 shows the longer time range from "several failures of boost" to manual " DOWN, GRAB_RESONANCE, DOWN, BOOST, and IMC_Locked". It showed the SERVO_SLOW changed from ~ 0.1 to around zero, and also that SERVO_NPRO_TEMP drifted up. This shows that SERVO_NPRO_TEMP drift contributed to reducing the DC value in SERVO_SLOW, then it enabled BOOST and IMC relock.

Fig.3 shows several PT temperature changes for the last 3 days. PT06 is smoothly approaching the equilibrium temp. PT02/04 shows a strange up and down. These are because of unstable current supplier or some contacting point error in the cable that used to be observed as before. So, the smooth reduction is an expected phenomenon. SERVO_NPRO_TEMP also shows the same kind of drift.

Fig.4 shows the longer time span from several hours IMC lock to unlock and recovery. Before unlock, SERVO_FAST and SLOW showed larger signals. Also, SERVO_NPRO_TEMP drifted up.

Consequently, I guess the IMC unlock was caused by the signal saturation in somewhere because of

the insufficient balance between thermal path and PZT path,
temp drift in the PSL room after the activities.

Also, I guess the several times relock failures were caused by the large DC values in SERVO_SLOW during boot.

Images attached to this report

Comments to this report:

shinji.miyoki - 8:30 Monday 01 September 2025 (34971)

PMC HEATER control became crazy when IMC unlocked as Fig.1. Then SERVO_NPRO became suddenly around zero from 0.05.

Also, SERVO_SLOW shows ~ 0.1 again. In addition, SERVO_NPRO_TEMP did not show any changes as before. In these conditions, the relock IMC might be difficult.

Images attached to this comment

34971_1756681458_Screenshot from 2025-09-01 08-03-16.png

kenta.tanaka - 12:35 Monday 01 September 2025 (34976)

We removed the lid of the NeoLASE box to improve the ventilation around the NPRO laser box (fig.1), according to Miyoki-san's advice . We hope that the situation about temperature controls is improved.

Images attached to this comment

shinji.miyoki - 7:33 Tuesday 02 September 2025 (34982)

Last night, PMC was locked for ~ 9 hours. Although the lock itself was kept, we can see several noise excitation in the K1:PSL-PMC_MIXER signal as reported klog#34978. The excitation seems to be kHz-level glitches, not sinusoidal excitations as Fig.1 and 2.

When the PRFPMI+RF lock on December 23, 2024, the K1:PSL-PMC_MIXER signal amplitude seemed to be half compared with the present quiet state, and no glitches existed during the long lock.

Images attached to this comment

34982_1756764703_Screenshot from 2025-09-02 06-01-43.png

34982_1756765044_Screenshot from 2025-09-02 07-17-09.png

shinji.miyoki - 10:47 Tuesday 02 September 2025 (34986)

>When the PRFPMI+RF lock on December 23, 2024, the K1:PSL-PMC_MIXER signal amplitude seemed to be half compared with the present quiet state, and no glitches existed during the long lock.

Fig.1 is the data at the time.

While, Fig.2 shows the recent data. At this timing, K1:PSL-PMC_MIXER signal can be comparable in the last year. In addition, the amplitude of IMC-SERVO_SLOW is also comparable. While FAST is larger than before. We need to consider the crossover frequency for the precise comparison.

Images attached to this comment