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On-call intervention (General)

vardaro - 20:20 Friday 28 June 2024 (64618)

Faulty SC PLL

Today I was called by Fabio because the automation of the squeezing was not relocking anymore. I realized that the SC PLL was not able to relock anymore. I tried to move the SC laser in frequency but I never passed from a locking point.

The SC laser is never used in science mode so I decided to remove it from the automation:

I changhed the SC lokcing threshold in SQZ_MAIN.ini from 1.2 to -1.2

I changed line 2616 from ('LOCKED_PLL_SC', 'SQZ_LOCKING_NO_FC'), to ('LOCKED_PLL_CC', 'SQZ_LOCKING_NO_FC'),

and 2621 from ('SQZ_INJECTED_NO_FC', 'LOCKED_PLL_SC'), to ('SQZ_INJECTED_NO_FC', 'LOCKED_PLL_CC'),
then I changed the final state in the decorator SQZ_OK from LOCKED_PLL_SC to locked PLL_CC

To re-integrate the SQZ node in ITF lock should be enough change all the call in the state LOCKED_PLL_SC with LOCKED_PLL_CC
Further investigation on the SC PLL will be done in the next maintenance. This issue will not cause problem to the normal operation of SQZ in science mode

Comments to this report:

vardaro, gherardini - 19:23 Monday 01 July 2024 (64636)

Today I investigated the SC PLL issue.

Fig 1. You can see that the PLL unlocked before the unlock of the ITF and of the Squeezer (SQZ_MAIN_index). Simultaneously with SC PLL unlock we saw a drop on the PD DC power. So we started to think that we had a problem related to SC PLL laser. See fig 1

Today Fabio went to check the SC PLL Laser and he found that the electronic was off. He reswitched it on. After the re-switch on I had to move the Thermal locking point from 30300 bit to 31300 bit. This probably was caused by the fact that the laser was cold. After one hour the PLL unlocked. I realized that the Thermal working point was driting back but then the SC PLL was not locking anymore. I suspect a mode hop of the laser. It is not the first time that I found this behaviour of the laser. Will see if it will solve by itself as in the past.

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