Electrostatic actuators: from the GEO experience to the 2 nd generation requirements
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Transcript of Electrostatic actuators: from the GEO experience to the 2 nd generation requirements
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Electrostatic actuators: from the GEO experience to the 2nd generation requirements
Harald LückPerugia, 21.9.2005
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Mode CleanersOutput Mode Cleaner
GEO600 Length Control Systems
MichelsonInterferometer
Laser
25 MHz13 MHz37 MHz
15 MHz
10 MHz
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Hierarchical Control Test Mass Actuators
<10Hz
>10Hz
<0.1Hz 3mm
100 µm
4 µm
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HV
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Reaction Mass Mirror
Operating Principle
Dielectric in an inhomogeheous E-field:
Force along E
need bias voltagefor bipolar actuation
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Segmented ESD
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ESD connections
HV
HV
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ESD connections
HV
HV
LV
LV
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Reaction mass Mirror
~3 mm gapBare copper wires
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GEO600 ESD data
• ~3 mm gap between reaction mass and mirror
• 630 V bias, range 0-900V
900 V → 350µN force
→ about 3.5µm @DC
• F = U2 ε0 εr d3/2 A
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Sqrt circuits in MI loop
ESD: F U2
Sqrt circuits are necessary to give full linear force range for acquisition.
Drawback: sqrt circuits are noisy (1µV/sqrt(Hz)=100µV @HV)
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ESD: F U2
Sqrt circuits are necessary to give full linear force range for acquisition.
Drawback: sqrt circuits are noisy (1µV/sqrt(Hz)=100µV @HV)
Bypassing sqrt circuits after lock is acquired.
Sqrt circuits in MI loop
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Noise in MI loop
HVA noise = 100nV/sqrt(Hz) = 10µV @ HVA
HV-amplifier noise can be reduced by decreasing bias voltage or active noise suppression.
Suppressing noise introduced by loop electronics needs whitening
Whiten
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MI loop whitening / dewhiteningWhitening right after mixer:zero 3.5 Hzpole 35 Hz
Dewhitening for both split paths
Passive dewhit-ening done in HV path
dewhiten
dewhiten
dewhiten
Whiten
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Future needs/options
• Two (eight) segments to give different actuation ranges for acquisition- and run mode
(in prelim. design doc. for Advanced LIGO)
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Segments for different actuation ranges
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Future needs/options
• Two (eight) segments to give different actuation ranges for acquisition- and run mode
(in prelim. design doc. for Advanced LIGO)• Change actuation range (noise) by changing
bias voltage (nonlin. effects)
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Future needs/options
• Two (eight) segments to give different actuation ranges for acquisition- and run mode
(in prelim. design doc. for Advanced LIGO)• Change actuation range (noise) by changing
bias voltage (nonlin. effects)• Investigate problems associated with charged
mirrors. Can be minimized by using AC (8192 Hz in Ad. LIGO?) actuation and using symmetrical voltages.
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U
F
Bias Reduction
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Reaction Pendulum:
3 coil-magnet actuators at intermediate mass, range ~ 100µm
Electrostatic actuation on test mass bias 630V, range 0-900V= 3.5µm
Hierarchical Control Test Mass Actuators
<10Hz
>10Hz
<0.1Hz