1 commissioning meeting, cascina, 5.12.2005 la electronics noise budget ● sources of electronic...
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1 Commissioning meeting, Cascina, 5.12.2005
LA electronics noise budget
● Sources of electronic noise● C7 electronic noise
● Electronic noise for optimized power● Some conclusions
2 Commissioning meeting, Cascina, 5.12.2005
Scheme of LA electronics
ADC noisePreamp. noise
Shot noise
Low-pass filter
AC: Gain 200
DC: Gain 1
diff. sig.
non-diff.sig.
Non-optimal treatment of DC signalsdominated by ADC noise(but were not foreseen as error signals)
VMEQD box
3 Commissioning meeting, Cascina, 5.12.2005
Principles of calculation
Calculate electronic noise at each quadrant diodeAC and DC signals
Reconstruct error signalsUsing C7 matrix
Pass through DSP correction filters
Obtain mirror motions through suspension transfer functionsLA loops closed
Suppose asymmetry (10, 1, 0.2 mm) => length noise
Two cases1. C7
using measured QD DC powers
2. Optimized DC powers50% of saturation power
4 Commissioning meeting, Cascina, 5.12.2005
C7 matrix
ThetaX PR BS NI NE WI WEB2_q1_DC 2.5 -4.5 -6.4 15B5_q1_DC 10B2_q1_ACp -24 9.41 17.9 5.38B1p_q1_ACp 0.052 -0.108 0.0375 1 0.0729B7_q1_ACq 0.042 -0.035 0.375 -0.027B7_q2_ACq 0.042 -0.035 0.375 -0.027B8_q1_ACp -0.25 0.65 0.052 0.071B8_q1_ACq -0.25 -0.65 -0.052 -0.071
ThetaY PR BS NI NE WI WEB2_q1_DC 1B5_q1_DC 10B1p_q1_ACq 1B7_q1_ACp 0.33 0.36B7_q2_ACp 0.68 0.36B7_q2_ACq -0.36 -0.36B8_q1_ACp -0.46 -1 -0.36B8_q2_ACp 1
ThetaX has undergone second diagonalization => mixing of all signals
5 Commissioning meeting, Cascina, 5.12.2005
Electronics noise vs. C7 noise (WE tx)
6 Commissioning meeting, Cascina, 5.12.2005
Electronics noise vs. C7 noise (WE ty)
Pure DC signal
7 Commissioning meeting, Cascina, 5.12.2005
Electronics noise vs. C7 noise (NE tx)
?
8 Commissioning meeting, Cascina, 5.12.2005
Electronics noise vs. C7 noise (NE ty)
9 Commissioning meeting, Cascina, 5.12.2005
Electronics noise vs. C7 noise (NI tx)
10 Commissioning meeting, Cascina, 5.12.2005
Electronics noise vs. C7 noise (NI ty)
11 Commissioning meeting, Cascina, 5.12.2005
Electronics noise vs. C7 noise (BS tx)
12 Commissioning meeting, Cascina, 5.12.2005
Electronics noise vs. C7 noise (BS ty)
13 Commissioning meeting, Cascina, 5.12.2005
Electronics noise vs. C7 noise (PR tx)
14 Commissioning meeting, Cascina, 5.12.2005
Electronics noise vs. C7 noise (PR ty)
15 Commissioning meeting, Cascina, 5.12.2005
Total LA electronics noise (C7, calculated)
WE ty pure DC error signal => no extra noise vs. AC
WI under local controlSimulated WI LA curves for comparison
C7 noise not limited byLA electronics noise
(but: excess noise)
16 Commissioning meeting, Cascina, 5.12.2005
Influence of QD power
Can gain ~ factor 10by increasing QD powers
17 Commissioning meeting, Cascina, 5.12.2005
Noise budget (C7)
ADC noise (= DC noise)is not dominating, butclose => second diagonalization (tx) has spoiled signals by reintroducing DC signals everywhere ?
18 Commissioning meeting, Cascina, 5.12.2005
Influence of mirror centering (optimized powers)
Without optimized matrixnor optimized filters: => need LIGO centering precision (0.2 mm)
19 Commissioning meeting, Cascina, 5.12.2005
Noise budget (optimized, 0.2 mm)
Still some effort neededat low frequencies
20 Commissioning meeting, Cascina, 5.12.2005
Contribution of mirrors (optim. powers)
NI ty filter difficult to improve? => try combination of EM + HH optimizations
21 Commissioning meeting, Cascina, 5.12.2005
Conclusions I
We can go quite far => LF design sensitivityusing present matrix and filters
but improvements hopefully possible
using DC signalsif optimizing QD powerif centering mirrors very well
Maximization of power on QD's is important
DC signals don't have more electronic noise than AC signalsTypical levels: AC 50 µV/rtHz DC 3 µV/rtHzLower DC electronic gain is not compensated by higher matrix gain
B2 DC signal seems to have high sensitivity (good SNR)
"second diagonalization" seems to spoil some signalsbut still same order of magnitude than AC signals
Other reasons for getting rid of DC signalsGet rid of laser technical noise at 6 MHz ?Seismic noise ?
22 Commissioning meeting, Cascina, 5.12.2005
Conclusions II
Extra noise observed on NI, BS, PR mirrorsNot limited by electronic noise at 50 HzC7 observation:
NI ty injected noise into dark fringe=> filter roll-off had to be improved
Origin of extra noise- Related to WI local control?- Diffused light?
same noise seen on B7, and on reconstr. signals using B7/B8
- QD miscentering?same noise seen in longitudinal noise (GV)
23 Commissioning meeting, Cascina, 5.12.2005
Conclusions III
ProblemsFeedback gains not well known
Optical matrix not calibrated
PR, BS influence on length noise not yet included
To be doneDevelop optimized correctors
for the 10-20 Hz range
Find optimized matrixUnderstand DC-AC noise questionInclude PR, BS contributions to length noise
24 Commissioning meeting, Cascina, 5.12.2005
End
25 Commissioning meeting, Cascina, 5.12.2005
Electronics noise vs. C7 noise (WI tx)
Local control
26 Commissioning meeting, Cascina, 5.12.2005
Electronics noise vs. C7 noise (WI ty)
Local control
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