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Lisa Barsotti - University and INFN Pisa –
on behalf of the Virgo Collaboration
CASCINA - January 24th, 2005ILIAS
Locking of Full Virgo
Status of VIRGO
VIRGO Optical Scheme
BS NIWIPR
3-km Fabry Perot cavities in the arms
Commissioning PlanSteps of increasing complexity:Steps of increasing complexity:
Sept 2003 – Feb 2004Sept 2003 – Feb 2004
A SINGLE FABRY-PEROT CAVITY
PR misaligned
North Cavity
Commissioning PlanSteps of increasing complexity:Steps of increasing complexity:
Sept 2003 – Feb 2004Sept 2003 – Feb 2004
A SINGLE FABRY-PEROT CAVITY
PR misaligned
West Cavity • Check of the performances of the sub-systems
• Check of the control systems in a simple configuration
Commissioning PlanSteps of increasing complexity:Steps of increasing complexity:
Feb 2004 – Dec 2004Feb 2004 – Dec 2004
A FABRY-PEROT MICHELSON ITF
“RECOMBINED” MODE
PR misaligned
North Cavity
West Cavity
• Intermediate step towards full Virgo
• Start of noise analysis
Commissioning PlanSteps of increasing complexity:Steps of increasing complexity:
Since Sept 2004 Since Sept 2004
A POWER RECYCLED MICHELSON ITF
Final configuration
PR aligned
North Cavity
West Cavity “RECYCLED” MODE
Commissioning of a Single Fabry-Perot Cavity - I
WE
NENI
WI
BSPR
WE
NENI
WI
BSPR
T=8%
Transmitted Power
laser freq noise
& mirror
angular motion
Power Fluctuations
Demodulated osymmetric beam Control Scheme
Lock at the first trial 28th Oct 2003
Commissioning of a Single Fabry-Perot Cavity - II
C1 (14-17/11/2003)- North cavity and OMC locked
Three Commissioning runs in a single cavity configuration:
C2 (20-23/02/2004)
- C1 + Automatic alignment
- West arm locked
C3 (23-27/04/2004)
- C2 + Laser freq stabilization
IMC control noise reduced
Transmitted Power
Commissioning of a Single Fabry-Perot Cavity – III
Sensitivity Progress
C1C2C3
C1 (14-17/11/2003)- North cavity and OMC locked
Three Commissioning runs in a single cavity configuration:
C2 (20-23/02/2004)
- C1 + Automatic alignment
- West arm locked
C3 (23-27/04/2004)
- C2 + Laser freq stabilization
IMC control noise reduced
Commissioning of the Recombined ITF
NENI
WI
BS
WE
NENIBSPR
Commissioning of the Recombined ITF
NENI
WI
BS
WE
NENIBS~ 1 W
PBS
10 W
P0
PR
20~1
500binedSens_RecomledSens_Recyc
PBS expected in recycled mode ~
500 W Sensitivity ~ BSPStart of some noise
characterization
( 500 W)
Recombined ITF Optical Scheme
1
5
7
8
2
WE
NENI
WI
PR
WE
NENI
WI
PR
T=8%
BS
Reflected beamAsymmetric beam
West Transmitted beam
North Transmitted beamPick-off beam
Recombined ITF Optical Scheme
1
5
7
8
2
WE
NENI
WI
PR
WE
NENI
WI
PR
T=8%
North Cavity
West Cavity
Simple Michelson
BS
3 d.o.f. ‘ s to be controlled: Lengths of the kilometric arms: L1 and L2
Michelson asymmetric length: l1 – l2
fields not mixed
L1
L2
l1
l2
Recombined ITF – Lock Acquisition
North arm
West arm
Michelson length
Lock of the two arms indipendently with the end photodiodes
Corrections sent to NE and WE
Lock of the michelson with the asymmetric port signal
Corrections sent to BS
8_demod
7_demod
1_demod
2_quad
Recombined ITF - Linear Locking
2_quad
North arm
West arm
Michelson
2_phase 1_demod
End photodiodes very usuful for lock acquisition but too noisy
Cavities controlled with the reflected and the asymmetric beams
Common mode of the
cavities
Differential mode of the
cavities
Commissioning Run C4 - June 2004
ITF controlled with the reflected and the asymmetric beams
Automatic alignment of the cavities
Laser frequency stabilized to cavities common mode
Cavities common mode locked to reference cavity
Output Mode Cleaner locked on the dark fringe
Tidal control on both arms
Recombined Data Taking Mode
Commissioning Run C4 - June 2004 5 days of run
Longest lock ~ 28 h
Lock losses understood
h reconstruction on line
Commissioning Run C4: Noise
CharacterizationCoupling of IB resonances into the
michelson controller signal due to a mismatch between modulation
frequency and input mode-cleaner length
C4
After frequency modulation
tuning
Michelson controller signalsee Flaminio’ s
talk
After C4 July – August
Upgrade of the terminal benches -> Re-tuning and improvement of the linear automatic alignment
Suspension full hierarchical control started
Commissioning of the Recycled ITF started
Effect of the backscattered light in the IMC -> attenuator installed between the IMC and the ITF
Mid September: Re-Start
October – November: -> Recombined ITF locked with the full hierarchical control of the end suspensions
-> ITF locked in recycled mode
Suspension Hierarchical Control
10-1
100
101
102
103
10-20
10-15
10-10
10-5
Actuators noise: current status
Frequency (Hz)
m/H
z1/2
Reference Mass - Mirror Actuators NoiseFilter #7 - Marionetta Actuators NoiseVIRGO Sentivity
103
Locking acquired and maintained acting at the level of the mirror
zz
x
y
marionette
reference mass
mirror Reduce the strength of the mirror actuators by a few 103 to reach
Virgo design sensitivity
Suspension Hierarchical Control
DC-0.01 Hz
0.01-8 Hz
8-50 Hz
Corrections sent to the marionette
Corrections sent to the mirror
Force on the mirror reduced of a factor 20
Switch to low noise coil drivers
TIDAL CONTROL
RE-ALLOCATION OF THE FORCE
Suspension Hierarchical Control
Single arm locked with the hierarchical control for the first time in July -> controllability of the superattenuator demonstrated
Last main result: hierarchical control of the recombined ITF in the C4 configuration, with automatic alignment and frequency servo engaged
Stable lock -> tested in the last commissioning run (C5, 2-6 December 2004)
SUMMARY
Lock Acquisition of full VIRGO
Simulations on a lock acquisition technique developed following the LIGO experience
Locking trials with this baseline technique (first half of July)
Attenuator installed (summer)
Restart of the locking trials with the baseline technique (21st September)
Debugging of the sub-systems
Establishement of theVariable Finesse lock acquisition technique (October)
Chronology
Recycled ITF: Base and Photodiodes
5
8
WE
NENI
WI
BSPR
WE
NENI
WI
BSPR
LLWW
LLNN
• MICH = ln-lw
• PRCL= lrec+(lN+ lw)/2
• CARM= LN+LW
• DARM= LN-LWllWW
llNNllrecrec
4 lengths to be controlled:
7
2Reflected beam
Asymmetric beam
West Transmetted beam
North Transmetted beam
1
Baseline Technique
Based on the LIGO technique
Multi–states approach
Dynamical inversion of the sensing matrix
Experimental Activity: Lock of Stable States - I
• Sidebands locked in the recycling cavity
2_quad
Reflected f-demod signals to control
MICH and PRCL
STABLE STATE 2STABLE STATE 2
2_phase
Experimental Activity: Lock of Stable States – II
• Sidebands locked in the recycling cavity, carrier locked in the FP
Reflected f-demod signals to control
MICH and PRCL
STABLE STATE 3STABLE STATE 3
2_quad
2_phase
From f-demod to 3f–demod signal
CARM contamination in the PRCL reconstruction
Frequency Response of the f-demod signal very sensitive to the ITF losses
CARM
DARM
PRCL
MICH
eee
eee
eeee
eee
eeee
eee
eee
eeee
Q
P
Qf
Pf
Q
P
Q
P
1.0384333
1253747
11461121
1411135
25614333
1513341
7116624
75135221
5
5
_3_2
_3_2
2
2
1
1
State 4 Simulated Sensing Matrix
PRCL Frequency Response - I
B2_f_phaseInput FP Mirrors Losses 1%o
Non - Minimum Phase
SIMULATION
PRCL Frequency Response - IIInput FP Mirrors Losses 1%o
B2_3f_phase
Minimum Phase
SIMULATION
VIRGO Lock Acquisition Scheme
1_phase
5_phaseREF BEAM
phase
REF BEAM quad
3f - Demod Signals
Good decoupling MICH / PRCL
Less CARM contamination in the PRCL
signal
Almost Diagonal Sensing Matrix
First Locking Trials
NORTH and WEST PowerRecycling Cavity Power
BS – PR Corrections
NE – WE Corrections
Drawbacks of the Baseline Technique: PR Transfer Function
PR transfer function
The lock acquisition technique is “statistical”.
transients, ringing
MARCH
OCTOBER
Compensation of the PR Resonances: critical, high
Q
The optical design of the ITF makes the response of the reflected 2_f signal very depending by the losses
Use of the 2_3f signal in the lock acquisition phase
The CARM contamination is anyway critical : use of SSFS is possible only in a steady state
regime
Drawbacks of the Baseline Technique:the CARM contamination
A new strategy: theVariable Finesse Lock Acquisition
The Variable Finesse Locking Strategy
“A recycled ITF with a low recycling factor is similar to a recombined ITF “
End photodiodes
Lock immediately the 4 degrees of freedom of the ITF on the half/white fringe (low recycling factor)
lock of PR prevents ringing and transient effects
lock of the cavities prevents CARM contamination
Bring the interferometer adiabatically from the half to the dark fringe increasing the recycling factor
The Variable Finesse Locking Strategy
NI NE
WE
WI
BSPR
Low Recycling Factor
Lock immediately the 4 degrees of freedom of the ITF on the half fringe:
end photodiodes to acquire the lock of the long cavities
simple michelson locked on the half fringe with the asymmetric DC signal
3f demodulated reflected signal to control the recycling cavity length
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-0.5
0
0.5
1
Half Fringe
The Variable Finesse Locking Strategy
yWest_cavit
tyNorth_cavi
10.5
0.51
west_phd
north_phd
End photodiodes start to see both the cavities:
We can not continue to control the arms We can not continue to control the arms indipendentlyindipendently
The Variable Finesse Locking Strategy
NI NE
WE
WI
BSPR
Low Recycling Factor
Laser frequency stabilization engaged
One of the end photodiodes used to control the differential mode of the cavities
Half Fringe
Laser stabilized on the common mode of the cavities
PR realigned Offset in the mich DC
error signal reduced approaching the dark fringe
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-0.5
0
0.5
1
5_ph
2_3f_ph
LASER
WEST TRANSM BEAM
5_q 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-0.5
0
0.5
1
The Variable Finesse Locking Strategy
From the DC to a demod signal to control the michelson length
The Variable Finesse Locking Strategy
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-0.5
0
0.5
1
Final Step : Final Step : To the Dark Fringe
ITF on the operating point
5_ph
2_3f ph
LASER
5_q
ASY BEAM 1_demod
RUNNING MODE: Switch to the main GW signal to
control the DARM mode: end photodiode
very noisy
The Variable Finesse Locking Strategy
POWER IN THE RECYCLING CAVITY
ITF not locked
The Variable Finesse Locking Strategy
Lock Acquisition
ITF locked on the dark fringe
“Variable Finesse” of the recycling
cavity
POWER IN THE RECYCLING CAVITY
Recombined interferometer (~ 60 mW)
Recycled interferometer (~ 17 W)
TPR=8% -> Recycling factor ~ 25
The Variable Finesse Locking Strategy
The Variable Finesse Locking Strategy
Recycling Cavity Power
Lock duration limited by the natural misalignment of the
mirrors
Longest Lock: 2h30
Need of the linear automatic alignment
( Usually about 30-40 minutes )
The Variable Finesse Locking Strategy
First lock of the recycled ITF on the end of last October
Stable lock of the recycled interferometer ~ 40-50 minutes
no linear automatic alignment yet next step
Locking procedure tested several times
lock acquired in few minutes
New original lock acquisition procedure established, combining end photodiodes, frequency servo, 3f-demod signal, slightly misalignement of PR mirror, and lock on the half fringe
1 day and half of test in the last commissioning run C5
SUMMARY
Commissioning Run C5 - December 2004
C5 configurations:
- RECOMBINED ITF as in C4 (automatic alignment, laser frequency stabilization servo, OMC locked)
+ suspension hierarchical control
-> end of the commissioning of the recombined ITF
- RECYCLED ITF (1 day and half)
Commissioning Run C5 - December 2004
Best VIRGO Sensitivity
RECOMBINEDRECYCLED
Noise hunting: C5 sensitivity
Short michelson control Recycling cavity control Laser freq control
COHERENCES with the GW signal
Sensitivity limited by control noise
Longitudinal locking control signal
BS tx local control
Local control signal
Noise hunting: C5 sensitivity• What about the noise at high frequency ?
?
• Observation: noise level change with time i.e. with alignment
Noise hunting: C5 sensitivity• 2 minutes of C5 data
Power on dark fringe Main ITF output
Other quadrature Averaged noise spectrum
Noise hunting: C5 sensitivity• Noise variation at high frequency vs alignment
Noise hunting: C5 sensitivity
• At low frequency (< 100-300 Hz)
- Switch OFF local controls (possible when automatic alignment will be used)- Use of less noisy error signals to control the ITF (2_3f -> 2_f)- Use of more complex controller filters - Reduce sensitivity to IMC length noise ( tune IMC length and Fmod)
• At high frequency (> 100-300 Hz)
- Implement ITF automatic alignment- Have a better look into noise when alignment is/will be better
Next Steps:
Something not undertood yet:
lock losses in C5 data
RECYCLING STORED POWER
Lock acquired, but
not stable
Stable Lock
Any evident difference in the two periods (analysis in progress)
Something not understood yet: the “JUMPS”
“Jumps” in the powers observed with the recycled locked
Recycling Cavity Power
Maximum power
Jumps very big -> less than half power
They can unlock the ITF
More frequent in these last weeks
Some days it was impossible to work
Not always present: any evident difference observed in the ITF status when jumps appeared with respect to the quite situation
First idea: jumps connected with the alignment of the ITF
Aligned position
Misaligned positions
Some experimental tests: NI misaligned of few urad
Jumps start to appear when the
mirror is misaligned of 2-3 urad
Same results obtained misaligning
the PR mirror
…but jumps are seen also with the “ well aligned” ITF (maximum stored power observed)
Some experimental tests: change of the PRCL error signal (2_3f) demodulation phase with respect to the alignment of the PR
Recycled Stored Power
PR - ty
2_3f demod phase
Aligned position
Aligned position: no jumps for a scan of several tens of degrees of the demodulation phase
More PR is misaligned and more the demod phase is critical
ITF locked in a “bad” way?
Sometimes the ITF works better - higher power, more stable - when it is still present an offset in the michelson error signal (5% out from the dark fringe)
A constant offset is present in the out loop reflected signal when the ITF is locked. The 2_f signal is planned to be used to control PRCL (switch 2_3f -> 2_f needed for noise reduction)
IN LOOP
OUT LOOP
Offset equivalent to 5 nm PR displacement
ITF locked in a “bad” way?
IN LOOP
OUT LOOP IN LOOP
OUT LOOP
When the switch 2_3f -> 2_f is done the stored
power decreases of the 50 %
Switch to 2_f
Stored Power
Refl 2_3f_phase signal
Refl 2_f_phase signal
The offset in the 2_f signal is independent from the alignment
conditions
An offset in the 2_3f signal ?
Something not understood yet: offset in the end signal
IN LOOPOffset
ITF LOCKED
Dark Fringe Power
ITF on the dark fringe
Stored Power
GW signalDARM error signal
MICH error signal
As soon as the switch from the end to the GW signal to control DARM is done, an offset appears on the end signal The dark fringe is “ darker” if the ITF is locked with the GW signal
An offset in the laser frequency servo?
The error signal used to control DARM is one of the end signals
It sees not only DARM, but also CARM
An offset in the laser frequency servo error signal could keep the ITF bad
locked in the CARM d.o.f
the end signal sees the CARM offset, which is transferred to the DARM d.o.f and which is visible on the dark fringe power
the GW signal sees only DARM, so it does not see the offset
could it explain also the offset in the reflected signal?
An offset in the laser frequency servo?
DARM error signal Ref 2_f_phase
OUT LOOP same offset
ITF locked with the GW signal, offset added to the frequency servo error signal
Offset Stored Power
Conclusions 1 year of commissioning
28th Oct 2003
First lock of the north cavity
26th Oct 2004
First lock of the recycled ITF
Next Steps
Improvement of the recycling locking robustness and understanding of jumps and offsets:
- real time simulation under development + dedicated shifts
Automation
- pre-alignment (in progress) and locking procedures (done)
Linear automatic alignment of the full ITF
- work started, other 3-4 weeks planned
Laser frequency stabilization optimization
- preliminary measurements done