K. Kawabe, J. Kissel, G. Mansell, D. Sigg
We've achieved the following in HAM1 today:
- Measured beam profile on LSC side (reflection side) of LSC/ASC REFL Beam Splitter (M6 on D1000313) down stream of the lens L1 (without LSC REFL A or LSC REFL B, or LSC A/B beam splitter in place)
- Re-installed LSC REFL A/B beam splitter, and LSC REFL A PD
- Installed new LSC REFL B PD
- Aligned beams on to LSC REFL A and B using LSC/ASC beam splitter, LSC A/B beam splitter
- Aligned LSC REFL A and B PD such that their reflections are dumped appropriately
- Verified the distances between LSC A/B beam splitter and each PD which we believe will result in a beam radius of ~240 um (details to be posted later)
- WFS B beam dump black glass** has been replaced, as discussed in LHO aLOG 45279
- We found that physical ASC REFL B was read out in the digital system as ASC REFL A (both DC and RF), and vice versa
- Attempted to figure out what was wrong with ASC REFL A segment 4 DC, tried many things including various cable swaps, ended up reverting to the original configuration as we found it. DB25 for physical ASC REFL B (digital ASC REFL A) was not secured at all. This was reseated and secured. This somehow repaired the faulty segment, but we can't really identify exactly what fixed it.
- We measured the laser power at various points in HAM1 with a dodgy OPHIR power meter:
IMC_PWR_IN reports 250 mW.
Inside HAM1, that same input beam as it flies through HAM1: 234 mW
IFO REFL beam coming back into HAM1: 227 +/- 50 mW
REFL AIR path: 4.1 +/- 0.5 mW
In front of LSC REFL A: 1 +/- 0.5 mW
In front of LSC REFL B: 0.87 +/- 0.5 mW
LSC-REFL_A_LF_OUT16 reports 0.8 +/- 0.01 mW
LSC-REFL_A_LF_OUT16 reports 0.735 +/- 0.01 mW
- We checked all new components for being bolted to the table, and we cleared the table of all tools we used today.
**The existing black glass stock all appear to have water marks of some sort, so Keita took the best he could find, and used a pre-soaked wipe to clean off what fogginess he found.
We have left the IFO with both the main PSL input light pipe and the ALS light pipe shuttered.
What's left to be done:
- Verify that LSC REFL A and B's RF signals are functional (we only verified that DC signals are functional). Currently the cable that connects the TNC to 5-way coax piece is missing at the chamber feedthrough.
- The chamber-closeout ground loop check
Detailed blow-by-blow log is attached. Also attached are some relevant screen captures of the state of things after we'd finished with the IMC locked on 250 mW input power, the IMs, RMs, and PRM aligned, and with the REFL DC centering loops engaged.
Pictures, and plot of LSC REFL path beam radius evolution to come in a bit.
We know that LSC-REFL_A RF is working. Only LSC-REFL_B needs checking.
We found the 5-way coax to TNC adapter made by Fil in the shop (but we didn't have stamina to continue).
- Attaching the beam profile on the LSC-REFL PD path, as measured from lens L1. The LSC-REFL_A was placed 193 mm from the lens (if I remember correctly, Jeff will correct me if I'm wrong). When including the extra ~5mm optical path through the beamsplitter, which was not included in this beam scan, the beam radius at the photodiode surface should be ~200 um.
- Also attaching serial numbers and part numbers of the power meter (PD300-3W-SH) used to measure numbers quoted by Jeff above. We were tried two head/filter combinations and had some concerns about systematic uncertainty introduced by mismatched pairs of heads and filters.
| Part number | Serial number | |
|
Head |
1202411 | 73375 |
|
Filter |
1Z02411 |
64799 |
|
Display |
Z01500 | 120573 |
This alog addresses IIET 4526: Bad connection at D6 1C1 feedthrough on HAM1 (ASC-REFL_A_DC_SEG4 problem).
The feedthrough was switched earlier, alog 45337. On Saturday, we swapped the DB25 cables bewteen the REFL WFS to see, if the problem stays with the cable connection or the sensor head. After some confusion, we concluded the problems had disappeared. Not sure, if this was due to the feedthrough work or the connector swap at the head. We swapped the cable back to nominal, and we inserted breakout boards at the WFS interface chassis. There, we verified that each leg of all 4 DC signal readbacks of both WFSs were operational. We will check again after pump down, but for now the problem looks fixed.
For REFL the downstream WFS is A, whereas the upstream WFS is B. This is contrary to the usual convention, but it has always been like that and we didn't correct it during this vent.
Here're the collection of photos from the day. The full bank of photos can be found in the DCC under G1802204. I attach a few photo highlights, and those imperative information here.
A note on the beam profile measurement:
Keita reminded me that the photodiode surface protrudes from the case by 3.8 mm. The x axis on my beam profile fit is measured relative to the case. So the position of the diode is actally 3.8 mm before my guess in the above comment, at 194.2 mm. The beam radius here is (216, 232) um.