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Overview

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Overview

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  1. LIGO calibration during the S3 science runMichael Landry LIGO Hanford ObservatoryJustin Garofoli, Luca Matone, Hugh Radkins (LHO), Rana Adhikari, Peter Fritschel (MIT), Patrick Sutton (Caltech), Brian O’Reilly (LLO), Xavier Siemens (UWM), Gabriela González,Andres Rodriguez (LSU), Martin Hewitson (GEO)GWDAW9December 19, 2004Annecy, France

  2. Overview • Calibration basics • Calibration improvements for S3 • Line strengths in all IFOs • Accurate DC calibrations • Checks on systematics • S4 photon calibrator

  3. IFO review

  4. Calibration method • Measure open loop gain G, input unity gain to model • Extract sensing function C=G/AD from the model • Produce response function at time of the calibration, R=(1+G)/C • Now, to extrapolate for future times, monitor single calibration line in AS_Q error signal, plus any changes in gain beta, and form alphas • Can then produce R at any later time t, given alpha and beta at t • Independent time-domain method (spearheaded by Xavier Siemens with input from Martin Hewitson) uses frequency domain filters as input. Calibrated frames available for use by analysis groups • Xavi also demodulates lines, which allows for a nice check on alphas and betas (frequency domain method assumes alpha and beta real, whereas demodulated lines are complex)

  5. Sample error budget: S2 H1

  6. Calibration improvements I Effect of line amplitude on error in product of alpha and beta

  7. S3 V3 a,b coefficients: L1 Over all of S3: a variation: 15% ab variation: 4% Error: 0.5%

  8. S3 Calibration errors • Errors from reference models in S3 ~ errors in S2 (5-10%) • Random variations, errors in alpha, beta (60 sec integration time): In S2: 0.7% (L1), ~3% (H1, H2).

  9. Calibration improvements IIDC calibration

  10. Calibration improvements II Asymmetric Michelson Lock configuration by feeding Back to ETM Instead of ~6% error on the ETM calibration, ~2% Lots of checks on actuation strength calibration: toggling, Michelson swinging, free swinging AS_Q, tidal actuators Important for hardware injections ETMx

  11. Calibration improvements IIIunderstanding systematics • Use of true dc calibration requires good understanding of systematics • Assess systematic error in digital filter compensation, e.g. dewhitening filters Digital Control signal Digital Anti-dewhitening filter DAC Analog dewhitening filter

  12. S3 response function R comparison • V2: assumes digital compensation is perfect • V3: uses hardware measurement

  13. S4: Photon calibrator • previously installed and tested – laser troubles with rotating polarization • recently reinstalled, awaiting laser safety approval • expect limited test for S4: independent check on magnitude of calibration (and timing, too) Oddvar Spjeld, LLO

  14. Conclusions • LIGO frequency domain calibration improving in accuracy with each science run • S3 calibration makes use of several new measurements • Anticipate independent check with photon calibrator for S4

  15. Magnitude: Phase: Contributions to the Error R(fi,t) = 1 + a(t) b (t) G(fi) a(t) C(fi)

  16. News on calibrationsince Aug LSC meeting Not enough!… • Coefficients: validation studies of “new” method (using demodulated line) • Models: • Codes were succesfully reviewed (P. Fritschel), no errors found. • V2 model version reviewed; V3 mods will need to be assessed • Work in progress on LHO models (to incorporate hardware/digital filters) • Work in progress: systematic model/measurement comparison for different calibration runs in L1. • Validation (use of!) X. Siemen’s h(t) frames has started…

  17. Hardware measurements

  18. S3 V3 a,b coefficients • V2 (from P. Sutton’s SenseMon) • b from SenseMon averaging input matrix • a from SenseMon’s line amp, b, and G0(f0) • V3: use Xavier Siemens’s code to generate demodulated lines in ASQ, DARM, EXC • Complex b = ( 1/D0)*(DARM-EXC)/ASQ • Complex a = -(D0/G0)*ASQ/DARM • Complex ab = -(1/G0)*(DARM-EXC)/DARM • Non-zero mean of imaginary part indicates errors in reference functions D0,G0 (at cal freq). • Standard deviations of imaginary parts are error estimates in real part (and depend on sampling frequency). • Compare consistency of Xavi’s output and existing model

  19. “New” method: validation steps H1, reference time G0 phase “error”:1.5 deg

  20. S3 V3 ab coefficient: H1

  21. S3 V3 ab coefficient: L1

  22. S3 V3 a,b coefficients: H1 Over all of S3: a variation: 4% ab variation: 1% Error: 0.3%

  23. H1

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