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Status of VIRGO. Lisa Barsotti - University and INFN Pisa – on behalf of the Virgo Collaboration. Locking of Full Virgo. ILIAS. CASCINA - January 24 th , 2005. WI. PR. BS. NI. 3-km Fabry Perot cavities in the arms.

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status of virgo

Status of VIRGO

Lisa Barsotti- University and INFN Pisa – on behalf of the Virgo Collaboration

  • Locking of Full Virgo

ILIAS

CASCINA - January 24th, 2005

virgo optical scheme

WI

PR

BS

NI

3-km Fabry Perot cavities in the arms

VIRGO Optical Scheme
commissioning plan
Commissioning Plan

Steps of increasing complexity:

Sept 2003 – Feb 2004

  • A SINGLE FABRY-PEROT CAVITY

PR misaligned

North Cavity

commissioning plan4
Commissioning Plan

Steps of increasing complexity:

Sept 2003 – Feb 2004

  • A SINGLE FABRY-PEROT CAVITY
  • Check of the performances of the sub-systems
  • Check of the control systems in a simple configuration

West Cavity

PR misaligned

commissioning plan5
Commissioning Plan

Steps of increasing complexity:

Feb 2004 – Dec 2004

  • A FABRY-PEROT MICHELSON ITF

“RECOMBINED” MODE

West Cavity

  • Intermediate step towards full Virgo
  • Start of noise analysis

PR misaligned

North Cavity

commissioning plan6
Commissioning Plan

Steps of increasing complexity:

Since Sept 2004

  • A POWER RECYCLED MICHELSON ITF

West Cavity

“RECYCLED” MODE

  • Final configuration

PR aligned

North Cavity

commissioning of a single fabry perot cavity i

Transmitted Power

WE

WE

WI

WI

PR

PR

NI

NI

NE

NE

BS

BS

Demodulated osymmetric beam

Control Scheme

Commissioning of a Single Fabry-Perot Cavity - I

Lock at the first trial 28th Oct 2003

Power Fluctuations

laser freq noise

& mirror angular motion

T=8%

commissioning of a single fabry perot cavity ii

Transmitted Power

Commissioning of a Single Fabry-Perot Cavity - II

Three Commissioning runs in a single cavity configuration:

  • C1 (14-17/11/2003)- North cavity and OMC locked

IMC control noise reduced

  • C2 (20-23/02/2004)
  • - C1 + Automatic alignment
  • - West arm locked
  • C3 (23-27/04/2004)
  • - C2 + Laser freq stabilization
commissioning of a single fabry perot cavity iii
Commissioning of a Single Fabry-Perot Cavity – III
  • Sensitivity Progress

Three Commissioning runs in a single cavity configuration:

  • C1 (14-17/11/2003)- North cavity and OMC locked

C1

IMC control noise reduced

C2

C3

  • C2 (20-23/02/2004)
  • - C1 + Automatic alignment
  • - West arm locked
  • C3 (23-27/04/2004)
  • - C2 + Laser freq stabilization
commissioning of the recombined itf11

Sensitivity ~

~ 1 W

10 W

P0

PBS

Commissioning of the Recombined ITF

PBSexpected in recycled mode ~ 500 W

WE

Start of some noise characterization

WI

( 500 W)

PR

NI

NI

NE

NE

BS

BS

recombined itf optical scheme
Recombined ITF Optical Scheme

8

West Transmitted beam

WE

WE

WI

WI

PR

PR

NI

NI

NE

NE

BS

7

North Transmitted beam

T=8%

5

Pick-off beam

2

Reflected beam

1

Asymmetric beam

recombined itf optical scheme13

L2

l2

l1

L1

Recombined ITF Optical Scheme

8

  • 3 d.o.f. ‘ s to be controlled:
  • Lengths of the kilometric arms:L1 and L2
  • Michelson asymmetric length:l1 – l2
  • fields not mixed

WE

WE

West Cavity

Simple Michelson

WI

WI

North Cavity

PR

PR

NI

NI

NE

NE

BS

7

T=8%

5

2

1

recombined itf lock acquisition

2_quad

1_demod

Recombined ITF –Lock Acquisition

8_demod

  • Lock of the two arms indipendently with the end photodiodesCorrections sent to NE and WE
  • Lock of the michelson with the asymmetric port signal Corrections sent to BS

West arm

North arm

7_demod

Michelson length

recombined itf linear locking
Recombined ITF - Linear Locking
  • End photodiodes very usuful for lock acquisition but too noisy
  • Cavities controlledwith the reflected and the asymmetric beams

West arm

Michelson

North arm

2_quad

2_phase

1_demod

Differential mode of the cavities

Common mode of the cavities

commissioning run c4 june 2004
Commissioning Run C4- June 2004
  • Recombined Data Taking Mode
  • 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
commissioning run c4 june 200417
Commissioning Run C4- June 2004
  • 5 days of run
  • Longest lock ~ 28 h
  • Lock losses understood
  • h reconstruction on line
commissioning run c4 noise characterization

Michelson controller signal

C4

After frequency modulation tuning

Commissioning Run C4: Noise Characterization

Coupling of IB resonances into the michelson controller signal due to a mismatch between modulation frequency and input mode-cleaner length

see Flaminio’ s talk

after c4
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 h ierarchical c ontrol

marionette

reference mass

103

y

mirror

z

x

z

Suspension Hierarchical Control
  • Locking acquired and maintained acting at the level of the mirror
  • Reduce the strength of the mirror actuators by a few 103 to reach Virgo design sensitivity
suspension h ierarchical c ontrol21

Corrections sent to the marionette

TIDAL CONTROL

DC-0.01 Hz

Corrections sent to the mirror

0.01-8 Hz

RE-ALLOCATION OF THE FORCE

Force on the mirror reduced of a factor 20

  • Switch to low noise coil drivers

8-50 Hz

Suspension Hierarchical Control
suspension h ierarchical c ontrol22
Suspension Hierarchical Control
  • SUMMARY
  • 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)
lock acquisition of full virgo

Lock Acquisition of full VIRGO

  • Chronology
  • 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)
recycled itf base and photodiodes
Recycled ITF:Base and Photodiodes

West Transmetted beam

4 lengths to be controlled:

8

  • MICH = ln-lw
  • PRCL= lrec+(lN+ lw)/2
  • CARM= LN+LW
  • DARM= LN-LW

WE

WE

LW

WI

WI

lW

PR

PR

NI

NI

NE

NE

BS

BS

lrec

lN

LN

7

North Transmetted beam

2

5

1

Reflected beam

Asymmetric beam

baseline technique
Baseline Technique
  • Based on the LIGO technique
  • Multi–states approach
  • Dynamical inversion of the sensing matrix
experimental activity lock of stable states i
Experimental Activity:Lock of Stable States - I
  • Sidebands locked in the recycling cavity

Reflected f-demod signals to control MICH and PRCL

STABLE STATE 2

2_phase

2_quad

experimental activity lock of stable states ii
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 3

2_phase

2_quad

from f demod to 3f demod signal
From f-demod to 3f–demod signal
  • CARM contamination in the PRCL reconstruction

State 4 Simulated Sensing Matrix

  • Frequency Response of the f-demod signal very sensitive to the ITF losses
prcl frequency response i
PRCL Frequency Response - I

Input FP Mirrors Losses 1%o

  • SIMULATION

B2_f_phase

Non - Minimum Phase

prcl frequency response ii
PRCL Frequency Response - II

Input FP Mirrors Losses 1%o

  • SIMULATION

B2_3f_phase

Minimum Phase

virgo lock acquisition scheme

3f - Demod Signals

VIRGO Lock Acquisition Scheme
  • Good decoupling MICH / PRCL
  • Less CARM contamination in the PRCL signal
  • Almost Diagonal Sensing Matrix

REF BEAM phase

5_phase

REF BEAM quad

1_phase

first locking trials

BS – PR Corrections

NORTHandWESTPower

Recycling Cavity Power

NE – WE Corrections

First Locking Trials
drawbacks of the baseline technique pr transfer function

MARCH

OCTOBER

Drawbacks of the Baseline Technique: PR Transfer Function
  • PR transfer function

The lock acquisition technique is “statistical”.  transients, ringing

Compensation of the PR Resonances: critical, high Q

drawbacks of the baseline technique the carm contamination
Drawbacks of the Baseline Technique:the CARM contamination
  • 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
the variable finesse locking strategy
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 strategy37

WE

WI

PR

NI

NE

BS

Half Fringe

The Variable Finesse Locking Strategy
  • Lock immediately the 4 degrees of freedom of the ITF on the half fringe:
  • end photodiodes to acquire the lock of the long cavities

Low Recycling Factor

  • simple michelson locked on the half fringe with the asymmetric DC signal
  • 3f demodulated reflected signal to control the recycling cavity length
the variable finesse locking strategy38
The Variable Finesse Locking Strategy

End photodiodes start to see both the cavities:

We can not continue to control the arms indipendently

the variable finesse locking strategy39
The Variable Finesse Locking Strategy
  • Laser frequency stabilization engaged
  • One of the end photodiodes used to control the differential mode of the cavities

WE

  • Laser stabilized on the common mode of the cavities

Low Recycling Factor

  • PR realigned

WI

  • Offset in the mich DC error signal reduced approaching the dark fringe

PR

NI

NE

BS

Half Fringe

the variable finesse locking strategy40

LASER

The Variable Finesse Locking Strategy

WEST TRANSM BEAM

  • From the DC to a demod signal to control the michelson length

2_3f_ph

5_ph

5_q

the variable finesse locking strategy41
The Variable Finesse Locking Strategy
  • Final Step : To the Dark Fringe

ITF on the operating point

the variable finesse locking strategy42

LASER

The Variable Finesse Locking Strategy

RUNNING MODE: Switch to the main GW signal to control the DARM mode: end photodiode very noisy

2_3f ph

5_ph

5_q

ASY BEAM 1_demod

the variable finesse locking strategy43

POWER IN THE RECYCLING CAVITY

The Variable Finesse Locking Strategy

ITF locked on the dark fringe

ITF not locked

Lock Acquisition

“Variable Finesse” of the recycling cavity

the variable finesse locking strategy44

POWER IN THE RECYCLING CAVITY

The Variable Finesse Locking Strategy

Recycled interferometer (~ 17 W)

TPR=8% ->Recycling factor ~ 25

Recombined interferometer (~ 60 mW)

the variable finesse locking strategy45
The Variable Finesse Locking Strategy

Longest Lock: 2h30

Recycling Cavity Power

( Usually about 30-40 minutes )

Need of the linear automatic alignment

Lock duration limited by the natural misalignment of the mirrors

the variable finesse locking strategy46
The Variable Finesse Locking Strategy
  • SUMMARY
  • 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
commissioning run c5 december 2004
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)
noise hunting c5 sensitivity

Recycling cavity control

Laser freq control

Short michelson control

COHERENCES with the GW signal

Noise hunting: C5 sensitivity
  • Sensitivity limited by control noise

Longitudinal locking control signal

Local control signal

BS tx local control

noise hunting c5 sensitivity50
Noise hunting: C5 sensitivity
  • What about the noise at high frequency ?

?

  • Observation: noise level change with time i.e. with alignment
noise hunting c5 sensitivity51
Noise hunting: C5 sensitivity
  • 2 minutes of C5 data

Main ITF output

Power on dark fringe

Other quadrature

Averaged noise spectrum

noise hunting c5 sensitivity52
Noise hunting: C5 sensitivity
  • Noise variation at high frequency vs alignment
noise hunting c5 sensitivity53
Noise hunting: C5 sensitivity

Next Steps:

  • 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
something not undertood yet lock losses in c5 data
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
Something not understood yet: the “JUMPS”
  • “Jumps” in the powers observed with the recycled locked

Recycling Cavity 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

Maximum power

slide56

First idea: jumps connected with the alignment of the ITF

  • Some experimental tests: NI misaligned of few urad

Jumps start to appear when the mirror is misaligned of 2-3 urad

Sameresults obtained misaligning the PR mirror

Misaligned positions

Aligned position

…but jumps are seen also with the “ well aligned” ITF (maximum stored power observed)

slide57

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

Aligned position

2_3f demod phase

  • 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
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)

IN LOOP

  • 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)

Offset equivalent to 5 nm PR displacement

OUT LOOP

itf locked in a bad way59
ITF locked in a “bad” way?

Stored Power

Switch to 2_f

When the switch 2_3f -> 2_f is done the stored power decreases of the 50 %

Refl 2_3f_phase signal

The offset in the 2_f signal is independent from the alignment conditions

IN LOOP

OUT LOOP

Refl 2_f_phase signal

OUT LOOP

IN LOOP

An offset in the 2_3f signal ?

something not understood yet offset in the end signal

Offset

IN LOOP

Something not understood yet: offset in the end signal

Dark Fringe Power

Stored Power

MICH error signal

ITF on the dark fringe

ITF LOCKED

DARM error signal

GW 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
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 servo62
An offset in the laser frequency servo?
  • ITF locked with the GW signal, offset added to the frequency servo error signal

Offset

Stored Power

Ref2_f_phase

DARM error signal

same offset

OUT LOOP

conclusions
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
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