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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: 15349
Entry time: Tue May 26 02:31:00 2020
In reply to: 15348
Reply to this: 15360
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Author: |
gautam |
Type: |
Update |
Category: |
LSC |
Subject: |
Lock acquisition sequence |
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Here, I provide some details of the sequence. Obviously, I am presenting one of the quickest transitions to the fully locked state, I don't claim that every attempt is so smooth. But it is pretty cool that the whole thing can be done in ~3 minutes.
See Attachment #1 for the labels.
- A --- Arms are locked on POX/POY, and EX/EY lasers are also locked to their respective arms. The phase tracker outputs are averaged in preparation for transitioning control from POX/POY to ALS.
- B --- Aforementioned transition has been realized. CARM offset of -4 is applied. Based on this calibration, this is ~ 4 nm.
- C --- PRM is aligned in preparation for 3f vertex locking. Between C and D, the long pause is because I also use this time to DC couple the ITM Oplev servos, which requires some averaging.
- D --- PRMI is locked. CARM offset reduction begins. Between D and E, I scan CARM through a resonance, and look at the necessary offset requried in the CARM_B (=RF) path. It is a mystery to me why this is required.
- E --- Ramp CARM offset completely to 0. Twiddle CARM_A and DARM_A offsets (=ALS path) to maximize the arm transmitted powers. Between E and F, you can see that the arm powers stabilize somewhat before any RF control is engaged (more on this later), which means we are approximately in the linear regime of the CARM PDH signal, and the switchover can be effected. As I write this, I wonder if there is any benefit to normalizing the REFL_11 error signal (=CM_SLOW) by the arm transmission for a broader capture range?
- F --- CARM_B and DARM_B (=RF) paths engaged. I ramp off the ALS servos between F and G using a 10 second ramptime.
- G --- IFO is now under RF control, ALS control has been turned off completely.
- H --- Rudimentary ASC is enabled. The ITMs are already running with DC coupled Oplev servos, and for the ETMs, I use the Transmon QPDs. The loop shapes/gains for this part haven't been finalized yet, but some improvement in the stability is seen.
This particular lock held for ~20 minutes so I could run some loop characterization measurements etc.
I am struggling to explain:
- Why POP22 goes to 0 when we zero the CARM offset? The arm length is such that the 2f fields don't experience any abrupt changes in reflectivity from the arm cavity for a wide range of offsets. This signal is the trigger signal for the PRMI LSC control - right now, I get around this problem by mixing in some amount of POP DC once the PRMI is locked. But if the lock is lost, this requires some EPICS button gynmastics to try and salvage the lock... I guess the 1f field components experience a different phase on reflection at various offsets, so maybe I should be looking at sqrt(POP22_I^2 + POP22_Q^2) instead of just POP22_I.
- Why is an error point offset required in the CARM RF path?
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