Transcript Document

LIGO calibration during the S3
science run
Michael Landry
LIGO Hanford Observatory
Justin 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)
GWDAW9
December 19, 2004
Annecy, France
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Overview
1. Calibration basics
2. Calibration improvements for S3
1. Line strengths in all IFOs
2. Accurate DC calibrations
3. Checks on systematics
3. S4 photon calibrator
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IFO review
G( f , t )  A( f ) (t )C( f ) (t ) D( f )
1   (t )  (t )G( f )
h( f , t )  R( f , t ) ASQ ( f , t ) 
ASQ ( f , t )
 (t )C ( f )
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Calibration method
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•
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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)
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Sample error budget: S2 H1
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Calibration improvements I
Effect of line
amplitude on
error in product
of alpha and beta
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S3 V3 , coefficients: L1
Over all of S3:
 variation: 15%
 variation: 4%
Error:
0.5%
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S3 Calibration errors
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•
Errors from reference models in S3 ~ errors in S2 (5-10%)
Random variations, errors in alpha, beta (60 sec integration time):

error

S3 variation

S3 variation
L1
0.5%
15%
4%
H1
0.3%
4%
1%
H2
0.7%
6%
2%
In S2: 0.7% (L1), ~3% (H1, H2).
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Calibration improvements II
DC calibration
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Calibration improvements II
Asymmetric Michelson
ETMx
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
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Calibration improvements III
understanding 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
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Anti-dewhitening
filter
DAC
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Analog
dewhitening
filter
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S3 response function R comparison
• V2: assumes digital
compensation is
perfect
• V3: uses hardware
measurement
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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
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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
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Contributions to the Error
  R    A    D  1  G 2   G

 
 


 R    A    D   1  G 4  G

 
 


2
Magnitude:
Phase:
2
2
 R   A   D 
2
2
2
1  G 
2
1  G
4
  G
2
 1  G 2    2 1  G 2
2
 
G
 
4 
4

1  G   
1  G

2
2

 G  
2
2
1  G 
2
1  G
4
G
2
R(fi,t) = 1 + (t)  (t) G(fi)
(t) C(fi)
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News on calibration
since 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…
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Hardware measurements
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S3 V3 , coefficients
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V2 (from P. Sutton’s SenseMon)
»
»
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V3: use Xavier Siemens’s code to generate demodulated lines in ASQ,
DARM, EXC
»
»
»
»
»
•
 from SenseMon averaging input matrix
 from SenseMon’s line amp, , and G0(f0)
Complex  = ( 1/D0)*(DARM-EXC)/ASQ
Complex  = -(D0/G0)*ASQ/DARM
Complex  = -(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
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“New” method: validation steps
H1, reference time
G0 phase “error”:
1.5 deg
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S3 V3  coefficient: H1
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S3 V3  coefficient: L1
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S3 V3 , coefficients: H1
Over all of S3:
 variation: 4%
 variation: 1%
Error:
0.3%
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H1
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