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yutaro.enomoto - 05:37, Friday 16 November 2018 (7011)Get code to link to this report
ALS CARM: Fast Path (Additive Offset Path) Engaged

[Nakano, Yokogawa, Sugimoto, Ushiba, Enomoto]

Tonight we tried to engage Additive Offset (AO) path of ALS CARM and it seemed that we succeeded.

What we did:
In the mine, we measured the transfer function of AO path, which means TF from IN2 of MC servo to the PSL frequency.
I will upload the TF we measured tomorrow.
Then designed the filter and tried to engage it.

Results:
I think we succeeded to engage it, since we were able to increase the gain to the level where the loop will be unstable if there is only MCL path.
Here are the current filter configuration and expected ALS CARM loop TF.

And the following shows the stablity of the arm transmission with this loop. It seems main laser frequency is barely kept around the resonance peak of X arm cavity.
 

Images attached to this report
7011_20181115212343_aopathalscarm.png 7011_20181115213341_filterestimation.png 7011_20181115213709_keepingresonance.png
Comments related to this report
yutaro.enomoto - 16:59, Friday 16 November 2018 (7017)

= Measurement of "actuator efficiency" of AO path =
Here is the measured TF from IN2 of MC servo to the output of the CARM servo.
Measurement condition is:
- Settings of SR560 (instead of Summing node): Gain 1, LPF 30Hz (while the current "nominal gain" is 5)
- IN2 gain of MC servo: -30dB, pol = '-'
- CARM servo settings: In2 gain is 0dB, IN2 pol = '+', fast gain is 5dB, fast pol = '-'
 

yutaro.enomoto - 17:10, Friday 16 November 2018 (7018)

= MEMO: Procedure of engaging AO path =

Current way to do it
1. switch on the MCL filter, while IN2 of CARM servo is disabled.
2. enable IN2 of CARM servo, which closes MCL loop of ALS CARM.
3. enable fast path of CARM servo, with fast gain of CARM servo and IN2 gain of MC set to be -32 dB and -30dB.
4. increase the fast gain to 7dB
5. increase the IN2 gain of CARM servo from 0dB to 2dB
6. decrease the MCL loop gain from 1 to 0.8
7. increase the IN2 gain of CARM servo from 2dB to 3dB
8. decrease the MCL loop gain from 0.8 to 0.7
9. increase the IN2 gain of CARM servo from 3dB to 6dB
10. decrease the MCL loop gain from 0.7 to 0.5
11. increase the IN2 gain of CARM servo from 6dB to 15dB
12. increase the fast gain of CARM servo from 7dB to 12dB
13. increase the MCL loop gain from 0.5 to 0.7
14. increase the fast gain of CARM servo from 12dB to 15dB
15.increase the MCL loop gain from 0.7 to 1
16. enable the boost in MCL path
17 enable the boost(s) in Common path of CARM servo.

yutaro.enomoto - 02:36, Saturday 17 November 2018 (7022)

Today OLTF of ALS CARM loop was measured.
The configuration is same as that of yesterday.
The overall gain was almost same as we expected