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Fast quadrant diode centering system LIGO-G070348-00-Z

Fast quadrant diode centering system LIGO-G070348-00-Z. SR1 alignment layout. WI. camera. Issue: better way of centering beam <-> quadrant diodes. BS. BMS. CoE. NI. camera. 6.26 MHz 8.35 MHz. DiE. PR. Foreseen change. GEO 600. Center diode on beam (few 100 mHz, noisy).

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Fast quadrant diode centering system LIGO-G070348-00-Z

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  1. Fast quadrant diode centering systemLIGO-G070348-00-Z

  2. SR1 alignment layout WI camera Issue: better way of centering beam <-> quadrant diodes BS BMS CoE NI camera 6.26 MHz 8.35 MHz DiE PR

  3. Foreseen change GEO 600 Center diode on beam (few 100 mHz, noisy) Center beam on diode (few 10 Hz) ILIAS collaboration GEO – Virgo (H. Grote)

  4. Test of GEO system on NE bench B7_q2 QD R. DeRosa, H. Grote, H. Heitmann, J. Marque, A. Masserot Log entry 12777

  5. Galvo feedback on NE bench (07/2006) • Digital feedback • Used existing Qr server (slightly modified) • 30 Hz bandwidth • Two shifts for making it work digital path Quadrant Electronics ADC Asymmetry computing Filter DAC DC signals Qr Server DOL (DAQ) Galvo Driver Correction signal Tilting Mirrors

  6. Galvo system performance 1 T-stage Galvo T-stage centering Centering fluctuations Q72 -1 normalized asymmetry Galvo centering

  7. Fast galvo centering: cost

  8. Fast galvo centering: planning to = now !

  9. Suggested proceeding • Start project NOW • 4 months available for hardware preparation: • => After SR1: mount 1-2 galvo steering assy’s • e.g. one on WE bench, one on detection bench • Observe for a few weeks • Then equip other QD’s • Pre/Post Virgo+ break? • Compatibility with new QD front end electronics • In central building: 4 QD’s on 1 CPU (Qa34) • CPU load due to • Correction signal computing for galvos • Anti-alias filtering for QD signals (for new QD front ends) • Exact CPU load to be determined; 2 GHz PC boards being prepared • Arrival date of new front end electronics not yet determined • => Maybe no problem

  10. SR1 news: Q81 centering problem QD centering Recentering Longitudinal signal becomes visible in Q81_AC signal (-> BS) if QD is miscentered => BS alignment drift Solutions • Compensate BS alignment offset with DC signal in sensing matrix But: AC signal not valid if miscentering too large • Geo could lend a fast quadrant centering system for Q81

  11. Start now => available at the end of SR1

  12. End

  13. Present centering accuracy North end Symm.port West end Dark fringe Q1p Q21 Q71 Q81 WSR10 Q82 Q22 Q72 Q51 Translation stage centering > 3 sec

  14. Requirements for centering With the present centering configuration (activates every few minutes) RMS change of a factor of 4 Extrapolating from these measurements… Taking a reasonable range around the “minimum”, the maximum DC asymmetry must be less than 0.1 G. Vajente Even with the best centering rate now possible (every 4-5 seconds) we can’t reach this precision.

  15. Galvo system performance II Galvo off Galvo on Error signals Galvo on Beam position fluctuations become visible in the correction signal Correction signals

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