With Shingo Hido

Summary

We performed the initial alignment for Xarm, Yarm, and OMC.

There were two points to be noted during the work:

• First, the IMC lost lock a few times. Most of the lock losses were recovered automatically, but once the IMC did not recover by itself. In that case, we manually changed the PZT offsets to recover the IMC lock, and then gradually returned all PZT offsets to 75.
• Second, the initial alignment sequence once stopped at INCREASE_LCS_POW_FOR_OMC. At that time, the IMC TRANS output stayed around 8.1 W. The PSL HWP had reached 169, while the REFL HWP was 152.266, slightly different from the target value. It is possible that the final fine adjustment of the HWP did not complete properly in that trial. After retrying the sequence, it passed this state and the alignment was completed.

Detials

Preparation

Before starting the initial alignment, we did the following checks and preparations.

• SRM and PRM were set to MISALIGNED.
• We confirmed that all Type-A suspensions could reach the LOCK_ACQUISITION state.
• The GRX and GRY shutters were open.
  • TR-GRX power was about 1.
  • TR-GRY power was about 1.
• PLLX and PLLY were confirmed to be in PLL_LOCKED.
• FIBX and FIBY were in SAFE due to the known DGS issue, but we proceeded.

Xarm alignment

For Xarm, the IX TCam image looked strange, possibly because of a different zoom or field of view. Therefore, we decided not to rely on the IX TCam image.

We requested the following states one by one:

• IRX_LOCKED
• GRX_LOCKED_WITH_IRX
• ALIGNING_XARM

During this process, the IMC lost lock about two times, but it seemed to recover automatically.

At ALIGNING_XARM, the GRX power was about 0.92, which was slightly low. We manually adjusted ITMX and ETMX as follows:

(IX-P, IX-Y, EX-P, EX-Y) = (9.4, -10.9, -12.0, -11.3) -> (8.4, -12.1, -12.8, -11.3)

After this adjustment, the GRX power increased to about 0.98. The IRX power stayed around 1.0.

Then we requested:

• RECORD_GOOD_VALUES_XARM
• OFFLOAD

Yarm alignment

For Yarm, we requested the following states one by one:

• IRY_LOCKED
• GRY_LOCKED_WITH_IRY
• ALIGNING_YARM

The alignment looked good, so we proceeded without manually adjusting the BS.

Then we requested:

• RECORD_GOOD_VALUES_YARM
• OFFLOAD

OMC alignment

For the OMC alignment, we first requested:

• IRY_LOCKED_FOR_OMC
• ENGAGE_OMMT2_TRANS_CENTERING
• ALIGNING_TO_OMC

The lock was lost during this process. We tried again by requesting:

• IRY_LOCKED_FOR_OMC
• ENGAGE_OMMT2_TRANS_CENTERING

but the lock was lost again, and this time the IMC did not recover automatically.

To recover the IMC, we manually changed the PZT offsets based on the DOF outputs.

• For DOF4-P:
  • The output had been around 23, but it was around -7.
  • We increased PZT1-P from 75 to 104.
• For DOF5-P:
  • The output had been around -46, but it was around -71.
  • We increased PZT2-P from 75 to 100.
• For DOF4-Y:
  • The output had been around -30, but it was around 0.
  • We started changing PZT1-Y from 75 toward 45.
  • During this adjustment, the IMC locked.
• DOF5-Y was not adjusted.

After that, IO reached PROVIDING_STABLE_LIGHT. We waited for a while and then gradually returned all PZT offsets to 75.

After the recovery, we requested IRY_LOCKED_FOR_OMC again. The IMC immediately lost lock once, but recovered automatically. The system soon reached IRY_LOCKED_FOR_OMC.

Then we requested:

• ENGAGE_OMMT2_TRANS_CENTERING

The sequence stopped at INCREASE_LCS_POW_FOR_OMC. At that time, the IMC TRANS output stayed around 8.1 W. We checked the HWP values and found:

PSL HWP  = 169REFL HWP = 152.266

The REFL HWP was still 0.266 away from the expected value, so the final fine adjustment may not have completed properly.

We retried the sequence again. Then, the sequence passed this state. In the successful trial, the HWP values were:

PSL HWP  = 169REFL HWP = 152

Then we requested:

• ALIGNING_TO_OMC

The OMC transmitted power, OMC-TRANS_DC_SUM_OUT16, reached about 30.5. The ground motion became somewhat noisy during this process, but it calmed down after a while, and the guardian state was successfully reached.

Finally, we requested:

• RECORD_GOOD_VALUES_OMC

The initial alignment up to OMC was completed.