Instrumented baffles for Virgo - Lluïsa-Maria Mir for the Virgo Collaboration - IGFAE
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Instrumented baffles for Virgo
Lluïsa-Maria Mir
for the Virgo Collaboration
Performance of actual Virgo 2 Sensitivity Status BNS range BBH range
O3 data taking 3 @https://gracedb.ligo.org/latest/
GW detector sensitivities 4
Ranges quoted for
1.4 M⊙+1.4 M⊙ BNS
and 30 M⊙+30 M⊙
BBH systems
@ Living Rev Relativ (2018) 21:3
https://doi.org/10.1007/s41114-018-0012-9
AdV+: Advanced Virgo upgrade 5
• Next large upgrade in Virgo, synchronized with LIGO
• Keep Virgo relevance in global network
• Main change is the implementation of large end mirrors
• All subsystems will improve their performance
• Divided in two phases
• Phase I (up to 2022): preparation during O3, installation before O4
• 40 W laser input power
• Signal recycling cavity
• Newtonian noise cancellation
• Frequency depending squeezing
• Phase II (beyond 2022): preparation during O3-O4, installation before O5
• 200 W laser input power
• Larger mirrors
• Larger beam
AdV+ expected sensitivity 6
AdV+ main sources of noise 7
• Only fundamental
noises
• 40 W input power
assumed
Importance of stray light control 8 • Large fraction (70%) of light in interferometer lost in the form of stray light • ITF full of passive (AR coated) baffles to eliminate diffused light across (99.5%) • No real control/monitoring on where light goes
Importance of stray light control 9
• Stray light origin is hard to identify and its
harmful effects difficult to mitigate
• Can occur at various places:
• Laser beam diffraction
• Scattering on surfaces and in substrate
of optics
• Small reflection on anti-reflective surface
of optics
• Stray light might hit something with vibration
and re-enter the main laser beam Simulation: most of the scattered
• Stray light might cause phase noises in the light concentrated at low angles
beam, indistinguishable from GW signal
Instrumented baffles? 10 • Beam not easy to localize during pre-alignment • Rough targets installed on baffles to visualize beam • Scattered light is monitored with cameras • Sensors embedded in baffles will allow fully monitoring of small-angle scattered light: • Catch possible high order modes falling out the mirror • Discover possible ageing, contamination or worsening of mirror surfaces • Need to study carefully: • Potential mirror contamination • Electromagnetic interferences with payload actuators • Tethering effects of possible new cables • Heat exchange with mirror or auxiliary mechanics • Mechanical interfaces and payload weight and balance
Input mode cleaner (IMC) 11
@ Advanced Virgo Technical Design Report, VIR-0128A-12
https://www.nikhef.nl/pub/departments/mt/projects/virgo/inputmode/Input mode cleaner (IMC) 12
• Current IMC operated successfully
• Mirror contaminated during
installation phase
• IMC round trip losses 200 ppm (larger
than required 100 ppm)
• Throughput smaller than expected
• Increased sensitivity to back-
reflected light
• Potential issue of radiation pressure
with increased power
• Want to improve control on payload
https://www.nikhef.nl/pub/departments/mt/projects/virgo/inputmode/IMC instrumented baffle 13 https://www.nikhef.nl/pub/departments/mt/projects/virgo/inputmode/ • Profit from replacement of IMC payload to install an instrumented baffle • Instrumented baffle can be tested immediately after O3 • Would serve as prototype and performance demonstrator for baffles of main mirrors in time for the phase II upgrade
IMC instrumented baffle requirements 14
• Maintain current performance of baffles in
terms of reflectivity and scattering
• Have no significant effect on super-attenuator,
payload and mirror
• Stringent constraints on
• Mechanical design
• Ultra-high vacuum compatibility of sensors
and readout electronics
• Readout strategy
• Heat dissipation
• Induced electromagnetic noiseIMC instrumented baffle design 15 • Two rows of photodiodes around inner diameter for good angular resolution • Four radial equiangular columns to know beam dispersion in radial direction • Each half-baffle 64 photosensors • PCB and electrical components are embedded in the baffle to minimize light scattering impact • Baffle thinned in some areas to allow space for these components • If additional scattering due to the presence of the gaps is unacceptable, we will consider filling them with an UHV compatible material
IMC instrumented baffle design 16
Current baffle design Instrumented baffle design
Component Weight (g) Component Weight (g)
Stainless steel 1887.47 Stainless steel 1645.95
Photodiodes 44.74
PCB 26.98
Electrical components 140 (estimated)
Glue 20 (estimated)
Cables 100 (estimated)
Total 1887.47 Total 1977.66
Estimated difference = 90.19 g
New center of mass has moved away 1.34 mm with respect to the non-
instrumented current baffleIMC instrumented baffle thermal simulation 17 • Baffle thermal gradient including main support structure when electronics are powered by 2.5 W and the temperature of the walls is 300 K • Between 2K and 4K are expected compared with the temperature achieved in the current baffle heated by the laser at a power of 25 W
Photosensors 18
• According to simulation
• 5x10-6 to 5x10-5 W/cm2 per watt of laser input power reach baffle
• A granularity of 1 cm2 allows detection of patterns produced by non-
perfect alignments of the system
• Need sensors of about 1 cm2, which will receive 0.1 mW to 3.5 mW of light
• Temporal precision needed ~1 Hz
• Should have properties similar to baffle
• Reflectivity below 0.5% to minimize the light non hitting the main mirror to
be reflected back
• Scattering off photosensors must be < 500 ppm
• No significant amount of outgassing
• Specific R&D with Hamamatsu
• Proposed solution: 7.69 x 7.69 mm2, sensitive area of 6.97 x 6.97 mm2, based on
S13955-01 photodiode, with ceramic support and underfilling removedPhotosensors robustness simulation 19
• Temperature in diode area after being directly
illuminated by a 30 W laser beam during 30 ms
and 1 W afterwards
• Temperature in region corresponding to nearby
sensor
• Even in this extreme scenario temperature of
baffle never goes beyond 50 CElectronics 20
• Digital readout output
• Sensor front end consists of an amplifier and an ADC input for each sensor
• All sensors in each half-baffle assembled in a single PCB
• Electronics biasing: single common cable, already installed
• Data transmission either wireless or optical fiber
• Demonstrator with multiple ways to transmit digital data wirelessly (Wi-Fi,
Bluetooth and Lora) being tested @VirgoFirst prototype 21 • Validate the Hamamatsu S13955-01 photodiode readout system • Get a platform for the photodiode characterization
First prototype 22 Linearity test Polarization test
Dedicated tests 23
• First reflectivity test @ICMAB on sensors indicates
coating is needed
• Scattering tests of full baffle to be done @ICMAB
and @EGO
• UHV checks: residual gas analysis @ALBA
synchrotron facility
• Aging tests and calibration
• Photodiode and electronics characterization:
• Linearity and gain of the output signal in the
range of expected light
• Photodetection efficiency as a function of
wavelength and temperatureDAQ and software control 24 • DAQ server to provide access to data generated by instrumentation • Functionality: • Hardware interface to enable communication • Continuous acquisition of data • Database to record data and other parameters (like errors) • Engineering UI for expert to access whole system functionality • Instrument interface to make information available to Virgo DAQ
Baffles close to main mirrors 25
New (heavier) mirrors will
be installed (need for a
complete new payload)
Might end up instrumenting
also baffles in cryostat (to
ground)Summary 26
• Stray light origin is hard to identify and its harmful effects difficult to mitigate
• Currently @Virgo scattered light is partly monitored with cameras
• IFAE plans to instrument baffles with photosensors to allow fully monitoring of
small-angle scattered light
@ M. Kraan and Th. S. Bauer, “IMC installation mirror procedure”, VIR-0435A-13You can also read
