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| 40m Log |
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 Tue May 26 02:15:36 2020, gautam, Update, LSC, Lock acquisition portal entry
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 Tue May 26 02:31:00 2020, gautam, Update, LSC, Lock acquisition sequence 
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Wed May 27 20:14:51 2020, Koji, Update, LSC, Lock acquisition sequence
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Tue May 26 02:37:19 2020, gautam, Update, LSC, DARM loop measurement and fitting
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Tue May 26 03:01:35 2020, gautam, Update, LSC, CARM loop
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Wed Jun 3 01:46:14 2020, gautam, Update, LSC, CARM loop
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Tue May 26 03:06:59 2020, gautam, Update, LSC, PRFPMI sensing matrix
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Tue May 26 03:26:58 2020, gautam, Update, LSC, Preliminary noise budget
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Tue May 26 14:32:44 2020, gautam, Update, LSC, Arm transmission RIN
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Wed May 27 19:36:33 2020, Koji, Update, LSC, Arm transmission RIN
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Thu May 28 18:36:45 2020, gautam, Update, LSC, Arm transmission RIN
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Fri May 29 00:34:57 2020, rana, Update, LSC, Arm transmission RIN
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Wed Jun 3 02:14:32 2020, gautam, Update, ASC, PRC ASC improves arm transmission RIN
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Fri Jun 19 16:30:09 2020, gautam, Update, ASC, Some thoughts about ASC
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Tue Jul 7 14:06:10 2020, gautam, Update, ASC, Some more thoughts about ASC
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Tue May 26 16:00:06 2020, gautam, Update, LSC, Power buildup diagnostics
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Wed May 27 17:41:57 2020, Koji, Update, LSC, Power buildup diagnostics
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Wed Jun 3 02:08:00 2020, gautam, Update, LSC, Power buildup diagnostics
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Wed Jun 3 01:34:53 2020, gautam, Update, LSC, Lock acquisition update portal
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Wed Jun 3 03:29:26 2020, Koji, Update, LSC, Lock acquisition update portal
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Wed Jun 3 11:40:56 2020, gautam, Update, LSC, Lock acquisition update portal
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Wed Jun 3 18:49:47 2020, gautam, Update, LSC, PRG and CARM signal sign
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Message ID: 15458
Entry time: Tue Jul 7 14:06:10 2020
In reply to: 15418
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| Author: |
gautam |
| Type: |
Update |
| Category: |
ASC |
| Subject: |
Some more thoughts about ASC |
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Summary:
I want to be able to run the dither alignment servo with the PRFPMI locked - I've been thinking about what the scheme should be, and I list here some questions I had while thinking about this.
Details:
- ITM Oplev DC coupling
- In the current scheme, I DC couple the ITM Oplev servos after the arms have been aligned to maximize POX/POY transmission.
- However, looking back at data from when the CARM offset is reduced (e.g. Attachment #1), it looks like the ITMs are being torqued quite a bit during this process (ITMX PIT changes by ~20urad, ITMY YAW by ~10urad in this particular lock attempt).
- So the spots are not actually being centered on the test-masses? I guess the spot position on ITMX isn't actually controlled because we have only one actuator (BS) for the XARM beam axis. Is it unexpected that ITMY gets torqued so much?
- It is unclear what would happen if the ITM Oplev servos are not DC coupled. I wonder if I'd still be able to reach the high circulating powers and then rely solely on the TR QPDs for the arm cavity angular control.
- Another possibility is to offload the DC part of the control signal to the optic's slow bias voltage slider, and then turn off the DC coupling. After that, the dither alignment can optimize the cavity alignment.
- Dither alignment at high circulating power
- I think that the system should work with the same settings as for the POX/POY locking, with the following changes:
- Scale the overall loop gain by the arm transmission.
- Change LSC2ASS matrix element from XARM/YARM ---> DARM.
Does this sound right?
- In light of the above, I was thinking that we should introduce a gain scaling field in the c1ass RTCDS model (like we have for the LSC power normalization matrix). Is it worth to go through the somewhat invasive process of model recompilation etc?
- With the PRFPMI locked, I am wondering if I can simultaneously run the dither alignment loops for all the DoFs. Probably not, especially for MICH, since the actuator is the BS, which is also the actuator for the XARM loop?
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