Yesterday night a drift of the power transmitted by the PMC had occurred. This has made the IMC input power much noisier and in turn the strain signal very glitchy. The recover of the power injected to the ITF via tapping in the reservoir of IPC1 (see 46980) was only effective in easing the life for the locking configuration, but of course it did not change the dynamical behavior - nor was it expected.

As reported, this drift was a due to a worsening of the throughput of the PMC cavity, so after discussion with Frederic Cleva, it was agreed with the commissioning coordinator to try and realign the beam sent to the PMC "ASAP".

So this morning I came on site, discussed with the operator on duty and, after the green light by both th the run coordinator and the commissioning coordinator, I went to the laser lab to perform the operation.

What I did [just for the record, you can skip itif you want the conclusios]: I

TF node down, INJ node down, metatron paused, BPC with DC ON mode, scanned the PMC to block the beam on the laser bench, once the beam blocked via the flip mirror, changed the lock trigger of the PMC with the trasmission of the PMC, then locked again the PMC, then obesrved on the beam dump the shape of the transmitted beam to spot some singature of misalignment. I realized the TEM00 is too intense for tthe TEM01 to be visible, so I switched to scan mode again and selected a scanning ramp so to have only the misalignment mode in the range. Tried to minimize it by looking at the peak intensity, but found out that looking at it on the beam dump and trying to make it as close to a laguerre as possible wa much more effective. The transmitted power of the PMC was larger and much more stable then before.

Then I restored the nominal operation for the laser bench and the BPC and had a look to the trasnmitted power of the IMC. It was larger than yesterday as expected, so I adjusted it to the value we set yesterday.

In the attached plots the effect of the operation:

1) PMC trasnmitted power before and after the realignment (more stable and larger value than before)

2) Range over time before and after the operation: too early to assess the glitchiness has gone, but seems better

PS: Now I do not remember anymore if I restored the trigger of the PMC to the quadrant on the EIB2, it could be still the transmission of the PMC. If this is the case, the hardware safety against the EIB going crazy is OFF. If oscillations occur until monday morning, please call immediately INJ on call. I will check on monday morning and, if it is the case, unlock and restore the safety.