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Electrostatic actuators: from the GEO experience to the 2 nd generation requirements

Electrostatic actuators: from the GEO experience to the 2 nd generation requirements. Harald Lück Perugia, 21.9.2005. GEO600 Length Control Systems. 25 MHz. Michelson Interferometer. 13 MHz. 37 MHz. 15 MHz. Laser. 10 MHz. Output Mode Cleaner. Mode Cleaners. <0.1Hz. <10Hz. >10Hz.

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Electrostatic actuators: from the GEO experience to the 2 nd generation requirements

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  1. Electrostatic actuators: from the GEO experience to the 2nd generation requirements Harald Lück Perugia, 21.9.2005

  2. GEO600 Length Control Systems 25 MHz Michelson Interferometer 13 MHz 37 MHz 15 MHz Laser 10 MHz Output Mode Cleaner Mode Cleaners

  3. <0.1Hz <10Hz >10Hz Hierarchical Control Test Mass Actuators 3mm 100 µm 4 µm

  4. HV

  5. Operating Principle Dielectric in an inhomogeheous E-field: Force along E need bias voltage for bipolar actuation Reaction Mass Mirror

  6. Segmented ESD

  7. ESD connections HV HV

  8. ESD connections HV LV HV LV

  9. ~3 mm gap Bare copper wires Reaction mass Mirror

  10. 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 = U2ε0εr d3/2 A

  11. 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)

  12. 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) Bypassing sqrt circuits after lock is acquired.

  13. Whiten 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

  14. dewhiten dewhiten dewhiten Whiten MI loop whitening / dewhitening Whitening right after mixer: zero 3.5 Hz pole 35 Hz Dewhitening for both split paths Passive dewhit-ening done in HV path

  15. Future needs/options • Two (eight) segments to give different actuation ranges for acquisition- and run mode (in prelim. design doc. for Advanced LIGO)

  16. Segments for different actuation ranges

  17. 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)

  18. 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.

  19. F U Bias Reduction

  20. <0.1Hz <10Hz >10Hz Hierarchical Control Test Mass Actuators • Reaction Pendulum: • 3 coil-magnet actuators at intermediate mass, range ~ 100µm • Electrostatic actuation on test mass bias 630V, range 0-900V= 3.5µm

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