Many people (Sheila, Jenne, Jeff K, Keita, Travis, Ed, others...)
It seems like there are at least three problems right now. The alignment problem seems nearly solved, but the difficulties we are having with ALS mean that it is hard to make progress.
Alignment progress today:
- Earlier this morning when we managed to get past our ALS problems, we were loosing lock in the CARM offset reduction, due to the locklosses that we used to have trouble with when the recycling gain was low. We modified the guardian to use different transmitted arm powers for the transition from TR CARM to REFL for CARM control, (see 43344 and 44075 ). This means that the final value of the TR_CARM offset is a convient way to trend the how the recycling gain that we get from our inital alignment has changed over time, the better the recycling gain the more negative the value is (see the first attachment). The recyclcing gain that we get from our inital alignment has been getting worse over the last few months, which has probably contributed to loosing lock durring the CARM offset reduction.
- This morning Jenne and I were manually aligning the IFO at various points (Jenne was adjusting the PRC in DRMI and I was adjusting CHARD to maximize REFL when we were in the guardian state CARM_OFFSET_REDUCTION. Then we were able to engage the ASC manually by stepping CHARD after some loops were on.
- Once we got the ASC engaged, we decided to try bringing the soft dofs manually towards the alingment where the beams are centered on the optics, using P2L gains of 0.85 and Y2L gains of 0, this improved all of our build ups at 2W, and gave us a recycling gain close to 48. Jeff and Jenne used the green beams to fin the inital alignment references for these spot positions.
- We lost lock, and Travis and Jenne did an initial alignment with the references set to bring the spots to the high recycling gain spot well centered on the optic. This worked well for reaquiring lock, the DRMI build ups looked better than they have been, the DRMI ASC worked fine and didn't need to be manually adjusted, and we arrived at resonance with a recycling gain of ~47. This seemed like a much more smooth acquisition, so we've left the initial alingment references there. You can see in the attachment that the TR_CARM to REFL CARM transition is happening at a higher arm transmission as well.
- Here is a summary of the locking attempts where we made it to engaging full IFO ASC today:
- allowed ADS to DOF3 (ITMY) to come on with the spot position centered, and doing things manually moved ITMY to the "August" position, engaging the ETM spot servos with their August positions about half way through the process for ITMY. This worked, but we lost lock after increasing the input power to about 15W, possibly because I had manually done something wrong with the SRC loops which didn't keep their error points 0 well durring the power up.
- left A2L gains at their August values, acquired with the spots in the midle because that is the way the initial alignment was done, and allowed ADS to come on as it is normally written in the guardian. This was rough, because CHARD P hit it's soft limiter, but we survived. I think that we probably don't need to have the CHARD soft limiter on once CHARD has engaged, so it might make sense to turn that off before engaging any ADS loops. (This is the lock where we made it as far as the ESD transition).
- Tried the same approach, but this time when CHARD hit it's soft limiter we lost lock.
- Set the A2L gains to be centered on the optic for the ADS engagement, this worked fine for the ITMY loop. Then I set all the values to their "August" positions, and engaged the ETM loops at the same time. This was too fast, and we lost lock.
ALS:
- The problem which has taken up the most time today is the ALS locking not working. The problem seems to be with the X arm green locking alone, the arm drops lock frequently. Jenne and Jeff noticed that the green WFS were picking up whatever glitches are happening and also misaligning the cavity, so they have disabled the WFS by setting the master gain for the X arm to 0. This seemed to help but we still have plenty of locklosses. We are also guessing that this is the reason why operators have been reporting that the green WFS for X aren't working well, so this problem might have been going on for a while now.
- Keita posted the observation that the X ALS laser has more glitches than Y, but this has been true for many months. 51306
- Getting tired of these locklosses, I went to the end station and tried reseting the laser current to 1.9, which was the value about a year ago, when the laser looked to be a bit more stable. Ed and I couldn't get the wireless to work, so he remotely used the medm to help me try to set the temperature. We didn't end up in a good position (looked like mode hopping), so we've reverted now. Starting (and final) settings: 2.036A, 27.17C trial settings: 1.908 A, 27.34C
- We have continued to have many ALS locklosses for the last 2-3 hours.
ESD transition lockloss:
- The one time we got to the coil driver state we made it through without a problem, unlike Corey's expirience last night 51288
- We made the transition from ETMX to ITMX ESD+ ETMY UIM+PUM without a problem, but lost lock later in this state (1249955066). It looks like we just lost control of DARM (saturating the ETMY pum) in the fraction of a second before the PRCL gain is increased.