KAGRA Logbook

IOO (OMC)

tatsuki.washimi - 17:04 Thursday 11 July 2024 (30363)

OMC PDs cabling

[Miyoki, Washimi]

We discussed for the new cabling of the OMC in-vac PDs, from the DGS racks to the OMC chamber.

The current cable racks around the OMC booth are too high (we can't access it without a tall ladder) and noisy cables (power lines, digital lines) are also running. We need new cable racks (H~2m) outside the OMC booth, +X side, specialized for low-noise cables.

I measured the required length for D-sub cables and found about 12m. (The current cables running the booth ceiling look too long for the new path and are not recommended for reuse.)
The number of current cables is 5 (DC PD, QPD1, QPD2, PZT, Zswitch ). Considering future additional usage, I reserved eight 15m D-sub9 cables from the machine room.

Images attached to this report

Comments to this report:

tatsuki.washimi - 15:08 Friday 06 September 2024 (31015)

[KTanaka, YokozaWashimi]

Today we aligned the new D-sub9 cables for

OMC DCPD
OMC QPD1
OMC QPD2
OMC PZT
Z switch
spare1
spare2

using the new cable lack.

After this work, we checked them. But we found

OMC DCPD A,B : Still noisy
OMC QPD1,2: The driver oscillation problem (?) happened again and we couldn't check the cabling noise.
OMC PZT: We couldn't check it without laser.
Z switch: worked

(Deatails will be reported later)

The today's final configuation of these cables are:

OMC DCPD : connected to the floor cable
OMC QPD1,2: disconnected
OMC PZT: connected by the new cable
Z switch: connected by the new cable

Images attached to this comment

takaaki.yokozawa - 15:34 Friday 06 September 2024 (31016)

> OMC QPD1,2: The driver oscillation problem (?) happened again and we couldn't check the cabling noise.
We approached several things.
All figures in blue were the darknoise spectrum before starting the measurement.

Fig.1. Spectrum after finishing the re-cabling
- As you can see, larger peaks appeared in QPD2 segments, but we noticed "someone locked the IMC without contact to us!" so we turned off the IMC lock and closed the IR shutter

Fig.2 Dark noise spectrum after closing the IR shutter
- After closing the IR shutter, we measured the spectrum again, but even QPD2 segments were noisy, there are not so sharp peak in 40 Hz.

Fig.3. Swap the cable of the QPD1 and QPD2 in the point of the feedthrough part.
- Unknown peaks appeared, that quite unknown.
- What was the trigger of such many peaks?
- We forgot to see the effect of the swapping the cable in the point of the feedthrough part.

Fig.4. Disconnected the cable in the point of the feedthrough part.
- Still some noisy channels were there even after disconnecting the cable in the point of the feedthrough part, we called to Ushiba-san, and Ushiba-san remembered the oscillation of the circuit problem, we will contact to Aso-san next week

Fig.5. Turned off the power of the QPD driver circuit
- Noise level became smaller, so QPD driver may have some trouble.

Additional to the upper work, we tried many things, but we forgot to record the spectrum, I am sorry
- backed to the QPD cable for previous one.
- disconnect the cable between QPD driver circuit and cable to distinguish the noise source
-

Images attached to this comment

kenta.tanaka - 16:07 Friday 06 September 2024 (31018)

After the replacement, we measured the dark noise spectra and confirmed whether the ZSW works or not. Fig. 1 is the results, brown lines is the dark noise when the cable passed through the OMC booth ceiling, green is when the cable passed through the new rack, the blue lines is when the cable was on the booth floor . Many peaks (4 Hz harmonics?) appeared after replacing the cable from the OMC booth floor to the new rack. We restored the cable to the floor, then these peaks disappeared. Unfortunately, laying the cable in a new rack doesn't seem to work... In this time, we left the cable on the floor.

Then, we confirmed whether the ZSW works or not after the replacement. red line is the dark noise when we switched the TIA from 100 Ohm(blue) to 400 Ohm. It seems to work. After this confirmation, we switched back TIA to 100 Ohm

Images attached to this comment