GRAVITATIONAL WAVES DETECTORS Fulvio Ricci Dipartimento di Fisica, Università di Roma Sapienza & INFN – Sezione di Roma
The Spectrum of Gravitational Waves Wave periods and Wavelength milliseconds --- tens [km] hours --- tens of Millions [km] years --- tens of Billions [km] GW Stochastic background of Astrophysical origin millions of years --- billions of billions [km] GW at the recombination z~1000 and re-ionization z~6 epoch
Hz Ground base Inteferometers Exploring the Universe with the GW Detectors Space Inteferometers Pulsar Timing B-modes of the CMB Hz
The LISA in preparation after the great success of the pathfinder mission:many technologies tested successfully! The monolithic optical bench The colloidal Thrusters of the spacecraft The test masses
The GW interferometers on the Earth are in operation
The GW Interferometer: the Optical Configuration
The noise sources concurring to define the sensitivity • For future Interferometer Thermal Noise contributions • In addition Quantum Noise can be the other main limiting noise source. Quantum Noise è Combination of radiation pressure and shot noise • If we want to increase the sensitivity at very low frequency we have to beat the Seismic and Newtonian Noise barrier
Control Loops In practice the control is based the following physical degrees of freedom L x - L y è DARM (L x + L y )/2 è CARM L y L y l x - l y è MICH l y l rec = l rc + (l x +l y )/2 è PRLC L x L x l x l sc = l sr + (l x +l y )/2 è SRLC The mirror suspended swings è Local control reduction è 1 µ m/s, then In addition we have to control the angular degrees of freedom Several nested control loops: Step 0 evaluate the residual technical noise to be added to intrinsic sources of Step 1 actuate to reduce further the residual velocity Step 2 feedback loop engaged noise mainly at low frequency
Sensitivity prediction: theoretical and experimental one i.e. intrinsic noise of the detector and technical noises
New Installation in the time window between O2 to O3 Virgo LIGO Higher laser power New ( more powerful ) laser Replaced 5 of 8 test masses (better optical Replaced the suspensions of the last stage to quality) reduce the thermal noise ( monolithic fibers) Added squeezed light injection systems Added squeezed light injection systems New baffles to mitigate scattered light New faraday isolator and photodiodes Improvements to various controls systems Improvements to various controls systems (seismic, alignment, etc) (seismic, alignment, etc)
Upgrades between O2 and O3 in VIRGO 18 Target sensitivity: 40-60 Mpc as horizon for a NSNS 1.4 M at SNR=8 Main benefit from putting back the monolithic suspension Removing the steel wire thermal noise from noise budget gives a 20 Mpc range increase Theoretical limit of this configuration: 80 Mpc @13W Main criteria applied to choose the new parts to be installed: just those new elements that they don’t require long commissioning time
Pre- installation: commissioning to cure glitches During O2 Post O2
Monolithic suspensions are back } } • 9 Done in less than four months Ø Arm valves closed on Nov 27, reopen March 19 Ø Include two weeks of commissioning Ø Faster than scheduled
Installation: additional highlights Squeezing bench provided by AEI – MAX Planck 14 – 15 dB squeezed vacuum ( then when we match to the main interferometer significant loss in the gain are added ) Stray light hunting restarted adding extra baffles New laser amplifier 70 W è 100 W New pre-mode cleaner We can inject in the ITF up to 50 W
Running a Quantum Optics Interferometer [(Hz) -1/2 ] (2019—04-03 23:05:54 UTC) 10 -19 VIRGO without squeezed vacuum VIRGO with squeezed vacuum 10 -20 10 -21 10 -2 10 -23 10 1 10 2 10 3 10 4 Frequency [Hz]
The aLIGO detectors Hanford Livingstone
LIGO status: major hardware upgrade at both LIGO sites • High power • Laser noise • Squeezing • Signal recycling mirror change – Stray light control – Electric field sensors – Test mass replacements Pre and post installation of the new baffles
Noise improvements from high power and squeezing: 120 Mpc Livingston case New installations and corresponding sensitivity improvements Credits: L Barsotti Hanford needs to improve low frequency noise in order to reach sensitivity goal for next observing run
Installation Sequence Credits : KAGRA coll.
Improved sensitivities O2 O2 O3 O2 cleaned O3 10 -21 L1 10 -21 Strain (Hz -1/2 ) Strain (Hz -1/2 ) 10 -22 H1 10 -22 10 -23 10 -23 10 -24 10 1 10 2 10 3 Frequency (Hz) 10 -24 10 1 10 2 10 3 Frequency (Hz) Virgo
O3 RUN O3 started in time on Mon Apr. 1 st 2019 and it will last for 1 year Better sensitivity than O2 for all 3 instruments. As planned, shorter than usual commissioning time at all three sites for the first week. Coordination between the sites to maximize 3-IFO operation. At least one instrument tries to remain online at any given time. Very good triple coincidence: so far more than 40%. At least two interferometers 80% of the time. Only 1.1% with no interferometer in observation mode.
Run status at the end of August 2019
New Events – Public Alerts https://gracedb.ligo.org/latest/ file://localhost/.file/ id=6571367.143264776
Example of a couple of SUPEVENTs: S190412m and S190408an FAR= 1.683x10 -27 Hz è 1 per 1.883x10 +19 years FAR= 2.81x10 -18 Hz è 1 per 1.1273x10 +10 years
KAGRA is joining the network
KAGRA project Kamioka mine, Japan 3 km, underground, cryogenic detector (20 K)
KAGRA: from Installation to Commissioning - I
KAGRA: from Installation to Commissioning - II
KAGRA: crucial milestone achieved !! Michelson + Fabry-Perot Interferometer Locked for the first time with the test masses cooled at low temperature!!! From the KAGRA logbook ---07:53, August 23, 2019 We are so happy to show the first sensitivity DARM in KAGRA!!
The Network in action nowdays GERMANY – 600 m USA - 4 km USA - 4 km ITALY – 3 km
Effective time The network in accuracy of a single detector the final part of σ t = ( 2 π ρ σ f ) -1 O3 ρ è SNR σ f è effective bandwidth of the signal USA – 4 km USA – 4 km JAPAN – 3 km ITALY – 3 km KAGRA
Transient Event Localization O2 localization : the smaller uncertainties when we have the 3 detectors : GW170814, GW170817, GW170818 Credits: S. Fairhurst Prediction for O4: Median 90% credible region for the localization area (volume) of BNS: 30−48 deg 2 ( 50–83 x 10 3 Mpc 3 )
O3 and future plans
The upgrade of the current detectors aLIGo+ AdV+ KAGRA + USA – 4 km USA – 4 km JAPAN – 3 km ITALY – 3 km KAGRA
POST O3 for aLIGO è aLIGO+ • Modest-cost upgrade to Advanced LIGO • Frequency-dependent squeezing • Larger beam splitter • Better mirror coatings / new test masses • Balanced homodyne readout Factor of 4 to 7 increase in observable volume Funding from NSF and UKRI with support from Australia Instrument Science White Paper LIGO T1600119-v4 public document
Instrument Science White Paper LIGO T1600119-v4 public document
Advanced Virgo+ • Phase I è budget secured ü Signal recycling (not done in AdV yet) ü Higher laser power (AdV run with 18 W so far) ü Frequency dependent squeezing (frequency independent squeezing already done in AdV) ü Newtonian noise cancellation • Phase II ü Further increase of laser power ü Larger and heavier end test masses : beam radius~10 cm radius , m ~ 100 kg ü Better coatings: lower mechanical losses, less point defects, better uniformity (gain will depend on coating R&D results at the end of Phase I)
AdVirgo+ O4 (Phase I) and O5 (Phase II)
KAGRA+ For KAGRA+, with limited time and resources, brodband improvement is not easy Plans with limited ambition: 4 different scenarios studied ü heavier sapphire mirrors ü silicon mirrors (more ambitious) ü sensitivity tuned at low frequency ü higher laser power (high frequency gain)
Moving forward the new 3G detectors • The GW detection and the beginning of the multimessenger astronomy stimulated a world wide acceleration toward 3G GW observatories • In Europe we are going toward the formation of a Einstein Telescope (ET) collaboration, a competition between 2 sites, candidate to host the infrastructure, the submission of an ET project proposal to the ESFRI roadmap • In US the idea of a giant 40km detector, named Cosmic Explorer, is now born and supported, as Conceptual Design Study, by NSF • We set up a global coordination committee (GWIC-3G) that is attempting to harmonise the efforts and to find synergies
Motivations for New Detectors Ø Expand the exploration to the entire Universe Ø Black holes through cosmic history ü Formation, evolution and growth of black holes and their properties Ø Understanding extremes of physics ü Structure and dynamics of neutron stars ü Physics of extreme gravity Ø Probing the transient Universe ü Gamma ray bursts, gravitational collapse and Supernovae Ø Beyond GR looking for new Physics: gravstars, wormholes, new particles and fields
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