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Entry  Wed Jan 29 14:49:48 2020, anchal, DailyProgress, BEAT, Beanote Spectrum vs FSS Gain Values Beatnote_vs_FSSGain.pdf
    Reply  Wed Jan 29 15:58:26 2020, anchal, DailyProgress, BEAT, Beanote Spectrum vs FSS Gain Values Beatnote_vs_FSSGain.pdf
       Reply  Fri Feb 7 09:57:32 2020, anchal, DailyProgress, BEAT, Spanned gain parameter space in NFSS and checked beatnote NFSS_Spanned_Beatnote_Variation.pdf
          Reply  Fri Feb 7 18:12:03 2020, anchal, DailyProgress, BEAT, Spanned gain parameter space in SFSS and checked beatnote SFSS_Spanned_Beatnote_Variation.pdf
             Reply  Mon Feb 10 11:07:33 2020, anchal, DailyProgress, BEAT, Spanned gain parameter space in PMCs and checked beatnote PMC_Spanned_Beatnote_Variation.pdf
                Reply  Thu Feb 13 15:27:18 2020, anchal, DailyProgress, BEAT, Further iterated back and forth to optimized FSS Gains. FSS_Gain_Span.pdf
Message ID: 2526     Entry time: Mon Feb 10 11:07:33 2020     In reply to: 2525     Reply to this: 2531
Author: anchal 
Type: DailyProgress 
Category: BEAT 
Subject: Spanned gain parameter space in PMCs and checked beatnote 

I took beatnote measurements and spanned gain values in the PMC to see if stability issues in PMC loops can be affecting the FSS downstream.


Method

  • I used BNspec.py with default settings (10 kHz bandwidth at 15.625 kSa/s for 60s) while spanning the parameter space of PMC gains.
  • The beatnote frequency was robustly within 2 kHz of 27.34 MHz during this whole measurement.
  • Overall experiment was run by spanParamSpace.py script.

Inference

  • I calculated the integrated total beatnote frequency noise in the frequency range 200 Hz to 1 kHz where the total noise is expected to be dominated by coating Brownian noise.
  • Unstable regions in the parameter space are clearly visible.
  • Ideally, the noise in beatnote frequency should have very minimal coupling with the gain values in PMC loops.
  • This has been found true indeed for the south side but not so much on the North side.
  • Very clearly there is a corridor from -3 dB to 8 dB in NPMC gain where noise remains low. We generally use 7 dB value.
  • But this might just be too bad PMC loop causing light amplitude noise in the output.
  • There is a bulge at 400 Hz in the beatnote freqeuncy noise. I can also see a broadened oscillation in PMC error signals around that frequency on both sides.
  • I'm afraid that maybe the North PMC is causing big mode mismatch at 400 Hz causing the noise in the beatnote frequency. Or is that not possible?

Data

Attachment 1: PMC_Spanned_Beatnote_Variation.pdf  32 kB  | Hide | Hide all
PMC_Spanned_Beatnote_Variation.pdf
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