1 commissioning meeting, cascina, 5.12.2005 la electronics noise budget ● sources of electronic...

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


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


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


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


Electronics noise vs. C7 noise (WE tx)


Electronics noise vs. C7 noise (WE ty)

Pure DC signal


Electronics noise vs. C7 noise (NE tx)

?


Electronics noise vs. C7 noise (NE ty)


Electronics noise vs. C7 noise (NI tx)


Electronics noise vs. C7 noise (NI ty)


Electronics noise vs. C7 noise (BS tx)


Electronics noise vs. C7 noise (BS ty)


Electronics noise vs. C7 noise (PR tx)


Electronics noise vs. C7 noise (PR ty)


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)


Influence of QD power

Can gain ~ factor 10by increasing QD powers


Noise budget (C7)

ADC noise (= DC noise)is not dominating, butclose => second diagonalization (tx) has spoiled signals by reintroducing DC signals everywhere ?


Influence of mirror centering (optimized powers)

Without optimized matrixnor optimized filters: => need LIGO centering precision (0.2 mm)


Noise budget (optimized, 0.2 mm)

Still some effort neededat low frequencies


Contribution of mirrors (optim. powers)

NI ty filter difficult to improve? => try combination of EM + HH optimizations


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 ?


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)


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


End


Electronics noise vs. C7 noise (WI tx)

Local control


Electronics noise vs. C7 noise (WI ty)

Local control

1 commissioning meeting, cascina, 5.12.2005 la electronics noise budget ● sources of electronic...

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