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AdV-INJ (General opto-mechanical layout, common parts construction, Installation and pre-commissioning)

gosselin, melo, lagabbe, spinicelli, derossi - 20:02 Friday 17 April 2026 (69012)

Beam realignement from PMC to BPC

After the work done by Bulten and co on the EIB rebalancing with started to work on the realignement of the beam from PMC output towards the BPC quadrant with the EIB blocked in its nominal position.
To do so we locked the PMC with the reflection as a trigger. The LB_M13 is still a beam sampler that reflect only about 1% of the PMC TRA. The power was also reduce at the PMC input by about 50%. As a result we were working with a beam of about 350 mW to do the alignment.
We started by aligning the beam into the apertures which are at the output of the LB, using LB M13 and LB M14. While arriving on the EIB, we noticed that the beam was relatively low, few mm below the usual working point (100 mm). This is not completly explained, we checked the apertures at the output of the LB that were effectively at 100 mm. This discrepency can either be due to a height difference between the two benches or it means that we are not well aligned in the lens (f = 1000) at the output of the laser bench. The heght of this last an not be set.
We decided to keep the pinholes as the horizontal reference for the beam at the output of the LB but to use M13 and M14 to get a beam propagating in the 100 mm plan on EIB. We did so and adjusted the height of the apertures at the output of LB.
From here we started the alignement of the beam on EB by setting the miror EIB M1a M1b and M1c. We used M1a and M1b to ensure that the beam was propagating in the 100 mm plan and in the right direction for the transmission of M1c that will be used both for ALS and for the BPL loop. Once it was done we moved M1c by hand both in horizontal shift and horizontal tilt to pass through the EOM and eventually reached the photodiodes downstream ( BPC QN DC and QF DC for example). We managed to get the expected DC on both quadrants about: 0.006 V for 0.35 W of PMC TRA while we usualy have about 1V for 60 W of PMC TRA.
From here we started to work on the alignment of the optics downstream of M1c.
We noticed that we were very high on PT_M1, also the Y of the BPC was quite out of range.
This is explained by the fact that the algnment on EIB as alwas been done with a beam that was slightly lower.
We decided to go on with a general realignment on EIB. At first we got the beam back in the 100 mm plan in transmission of M1c, using M1a and M1b, and check that we were indeed correctly passing through the EOM.
Then we used EIB M3 to get the beam centered at the exit of IPC1/ M4. Then we used the mirrors one after the other till M8 to center the beam on each other.
We eventually got some signals on both NF and FF QPD (note for the future : IBJM is convenient to visually check the FF).
We will go on with the final fine alignment on monday.

Comments to this report:

gosselin, spinicelli, derossi, melo, lagabbe - 21:21 Monday 20 April 2026 (69015)

Today we kept on working on the alignment.
First at low power and then we swap the LB M13 mirror that was reflecting only 1% of the power of the PMC transmission and put the nominal one that relfect it all.
Unfortunately we had to work again on the alignment but at high power. We managed to get a rough alignment with the PMC in scan at medium power (10W).
The beam was still low on the BPC QPD, we had to realign it by hand using M6 and M8. We eventually reach the values of TX TY X and Y that we had before starting the intervention.
There are still things to understand, especially the DC values of the PD and QPD that seems to be different, the IMC REFL seems to be different as well.

Side activity : we started to realign the beam inside the PMC diagbox.

gosselin, derossi, melo, lagabbe, spinicelli, boschi, piendibene - 19:58 Tuesday 21 April 2026 (69020)

1. Injection Line Alignment & Power Loss Investigation

We continued work on the alignment following suspicions of beam clipping in the EOM + FI + IPC section. Initial measurements revealed significant throughput issues:

Measured 50.4 W at the PMC output and only 24.2 W after EIB M5.
After rotating IPC1 for full transmission, power increased to 38.3 W.
Accounting for measurement uncertainties and the new BPL/ALS pick-off (~3%), we calculated total losses of 21%. This is significantly higher than the historical baseline of 10% (ref: 50224).

Realignment Actions: We performed a systematic high-power realignment. By optimizing the throughput at the output of the third EOM by moving EIB M1c and centering the beam through the FI and IPC using EIB M2/M3, we achieved the following:

Final Power: 39.4 W measured after M5 with 45.5 W at PMC TRA.
Final Loss: Calculated at ~14% (normalized via PMC TRA monitor: 39.4/45.5×0.566/0.572).
Outcome: Beam profile visually improved; alignment proceeded through the telescope to the BPC QPD.

2. INJ Recovery & Loop Status

BPC Board: Valerio and Marco investigated the BPC board. We are observing an unidentified saturation-like behavior on the PZT where it stops responding. However, by maintaining low PZT values, we successfully locked the BPC.
IMC Lock: After realigning SIB1 and the MC, the IMC was locked.
IPC1 Adjustment: Power was reset to previous levels by monitoring the IMC REFL signal in the unlocked state.
IMC AA : Locked in drift control. Need to work on the matrix with the new reflection
Current Status: The IMC reflection suggests a larger mode mismatch than previously observed. Transmission power is currently lower at ~15 W.
Pending: Investigation of mismatch causes (?)band fine-tuning of IMC loops (AA, PDH, offsets, and Transfer Functions).

3. Beam Pointing Line (BPL)

Set all optics in transmission of M1c.
Power Measurements: Found 20.5 mW on the FF QPD and 23 mW on the NF QPD. These values align with our theoretical expectations.
Pending: Verification of beam properties on both QPDs and functional checks of the QPD and PZT.

4. Additional Activities

PMC Diagbox: Performed fine alignment. Despite using the same mirror transmission as before, the monitor signal is limited to 0.62 V.
PMC Loop Stability: Reduced the loop gain to eliminate oscillations. This appears to have resolved the power fluctuations observed today
ALS: (See dedicated entry).