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

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