1 locking in virgo matteo barsuglia ilias, cascina, july 7 th 2004
DESCRIPTION
3 Virgo optical scheme West cavity F=50 North cavity F=50 Recycling cavity G=50 Dark fringe Fabry-Perot Michelson Power recyclingTRANSCRIPT
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Locking in Virgo Matteo Barsuglia
ILIAS, Cascina, July 7th 2004
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• Introduction: optical scheme, terms, etc…• Actors: Hardware, software, simulation • Results:
• Experience with a single arm (cavity locking, frequency stabilization, ouput-mode cleaner locking)• The recombined interferometer (almost all the controls working)• Full detector lock acquisition (preparation and first results)
Outline
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Virgo optical scheme
West cavityF=50
North cavityF=50
Recycling cavityG=50
Dark fringe
Fabry-Perot Michelson
Power recycling
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Standard base• MICH = ln-lw• PRC= lrec+(lN+ lw)/2• CARM= LN+LW
• DARM= LN-LW
LN
Lw
lw
lN
lrec
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Intro: photodiode names
• 3 signals for each photodiode: DC, ACp, Acq
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2 1
5 and 5_2f
In- phasequadrature
reflection Antisymetric port
Transmission north
Transmission west
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Detection system
InGaAs photodiodes 6.26 MHz (only 1 modulation)
16 bits ADC
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Last stage
Digital controls
Control signals(DOL’s)
Photodiodes signals(DOL’s)
Alignment Locking
3 for each suspension
trigger, signal processing, filtering
• 10 kHz sampling• VME based, homemade• software in C
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Mirror actuators
Reference mass
4 coils
40 mN
Beam splitter
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• Real time simulation package of the Virgo experiment• Written in C, configuration cards • produces frames • Can be interfaced to the real time control system (global control)
Siesta
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SIESTA
Control signalsPhotodiodes signals
Algorithms running in the global control
Siesta
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Control signalsPhotodiodes signals
Algorithms running in the global control
VIRGO
Siesta
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North cavity locking
north arm
Test: Locking
Autoalignment Frequency
stabilization tidal control
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Linearized error signal
No Linearized error signal
m
Lock acquisition speed threshold ~ 10 m/s
Signals and linearization
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Signals and simulation
Correction Transmitted power
Time domain Simulation (Siesta)
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Cavity first locking • Locking at the first trial• first lock ~ 1 hour• frequency noise
Transmitted power
Frequency noisereduction
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Lock acquisition statistics 24 locking events collected locking and delocking the cavity 23 lock acquisition at the first attempt, only 1 failed locking attempt
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Relative velocity between the mirrors computed for each locking attempt
8 m/s: maximum velocity for the lock acquisition success
12.5 m/s: velocity of the failed event
Failed locking attempt
v ~ 12.5
sμm
sμm
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2.5 m/s: mean value of the velocity
Lock acquisition statistics
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Cavity locking accuracy
3 picometers RMS
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Output mode-cleaner locking
1. Cavity locked with ~ 1% of the light
2. Mode-cleaner locked
3. Control transferred to this phd ~ 99% of the light
After OMC Before OMC
Sensitivity (m/Hz)
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Output mode-cleaner locking Transmitted P Reflected P 2
State TemperatureError signal
2 min
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Frequency stabilization- North cavity error signal sent to the input mode-cleaner (below 200 Hz) and to the laser (above 200 Hz)- Reference cavity error signal used to control cavity length at DC
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Recombined ITF
north arm
west arm
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Recombined ITF
10 W~ 1W
• Sensitivity ~ 201500PBS ~
(500 W)
• 3 d.o.f. decoupled • fields are not mixed • lock acquisition easy• no “dynamical effects”
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Lock Acquisition – OverviewB8_phase/B8_DC
B5_phase/B7_DCB2_quad
NE
WE
BS
Lock of the two cavities (independently) Corrections sent to NE and WE Lock of the michelson length Corrections sent to BS
3 Steps lock acquisition:
North arm
West arm
Michelson length
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Linear Locking - Overview
⊗B1p_phase
B2_quad
North arm
West arm
B2_phase
Michelson length
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Complete scheme
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Run C4
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reach the Virgo sensitivity: recycling
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• Technique choosen: use the LIGO one (developed by Evans et al.)• VIRGO and LIGO have the same optical scheme, and similar optical parameters.• VIRGO and LIGO have similar control systems (digital, quite similar sampling frequencies,…).• VIRGO and LIGO have similar simulation packages (real time, etc…)• pragmatic point of view …the LIGO approach works
• Few differences between LIGO and VIRGO • Pick-off signal different • Arm finesse in LIGO = 200 (Virgo =50) • Suspension and local controls system simpler in LIGO
• Reproduce the LIGO technique with SIESTA • only optics (TEMO00, no saturation, no superattenuators) • Include fine effects (saturations, etc…)
Full Virgo lock acq approach
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Full virgo lock acq approach very difficult to have the 4 d.o.f. satisfied, in a linear regime
• Sequencial & Statistical (the states are not stable)• used in LIGO, works well in 3 itf’s• lot of signal processing (linearization, dynamical matrix inversion)• simulation crucial
central cavity locked
central cavity + first arm all ITF locked
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Optical characherization
• parameters of the optical matix (~ 10 ) determined by simulation• very important to reproduce in simulation the optical behaviour of the interferometer • During the CITF the locking parameters (2) what dermined in this way• optical characterization is a strategic item
micdiffmichcommon
armdiffarmcommon
Assss
acq
acqacqacqacq
__
__
4321
Each element = K P(measured throughB7/B8/B5_2f)
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Simulation
West cavity Trans power
North cavityTrans power
Power inside the rec cavity
Sidebands power inside the rec cavity
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“step 3” locking • Lock of the central cavity (CITF) on the sidebands + lock of the north arm (on the carrier)
B2_Q
B2_PB1_Q
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Lock acquisition state3
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• Experience with a single cavity and recombined very interesting to understand the hardware/software/signals/simulations• Real time simulation crucial tool (understand signals, test algos, save commissioning time)• Hardware and software tested and performant (algos in C++, parameter in a database, etc…)
• This summer: try to lock the recycled interferometer and prepare linear lock and final frequency stabilization.
Conclusions and next steps