A DAS tuning was attempted in CARM. NULL 1F with the goal of reducing the power on B1p, in order to continue with the lock acquisition in LN3.
STEP 1:
| Reference | CH [W] | INNER DAS [W] | OUTER DAS [W] |
---|
W | on the ITF | 0.046 | 0.150 | 1.60→1.71* |
on the pickoff | 0.284 | 0.025 | 0.26→0.28 * |
N | on the ITF | 0.104 | 0.340 | 3.77→3.95 ** |
on the pickoff | 0.635 | 0.055 | 0.61→0.64 ** |
* The WI outer ring has been increased by 7 %
** In calculating the NI outer ring power increase, we took into account that 30% of the total applied power is required to compensate for the cold lens.
After this step, a slight improvement was observed in the sideband power and imbalance, but no significant change was seen in the B1p signal.
The ISC team attempted to reach LN3 by applying a MICH offset to reduce the B1p power to the level required for continuing the lock acquisition. However, a large offset (around 80) was needed, and the ITF did not remain locked (12.36 UTC).
Subsequently, the ITF relocked at CARM null without requiring any further tuning.
Two tuning steps were applied to the WI DAS: the WI outer ring power was increased in two steps, reaching 1.9 W. The last step was completed at 13:55 UTC.
Approximately one hour after this last step, the fringe level decreased to about 0.025 mW (from an initial level of 0.045–0.05 mW). At that point, the ISC team managed to reduce the B1p power to a suitable level by applying a MICH offset of approximately 30, allowing the lock acquisition to proceed. The ITF successfully locked in LN3 at around 15:03 UTC.
At 17:00 UTC, while the ITF was still in LN3, I applied an additional step to assess the effect of increasing the NI outer ring power. The increment was kept small to minimize the risk of an unlock in case the tuning direction was wrong.
The final DAS power values injected into the ITF are reported in the table below:
| Reference | CH [W] | INNER DAS [W] | OUTER DAS [W] |
---|
W | on the ITF | 0.046 | 0.150 | 1.9 |
on the pickoff | 0.284 | 0.025 | 0.31 |
N | on the ITF | 0.104 | 0.340 | 4.1 |
on the pickoff | 0.635 | 0.055 | 0.67 |
The effect of the last step on the NI outer ring still needs to be evaluated.
The lock acquisition still needs to be verified.
The mail signals during the tuning are shown in the attached figure.