1. LIGO-G070624-00-M LIGO - The Laser Interferometer Gravitational-wave Observatory Vibration and Facility Considerations (incomplete) Dennis Coyne TMT Vibration Workshop 16 October 2007

2. LIGO-G070624-00-M LLNL Seminar 2 Outline Ambient Environment »Seismic »Wind driven seismic »Acoustic Facility requirements Facility design Environment data sets Instrument seismic & acoustic isolation design »Initial LIGO –Passive isolation –Active quiet hydraulic isolation –Acoustic enclosures »Advanced LIGO –Lots of active isolation!

3. LIGO-G070624-00-M LLNL Seminar 3 LIGO Observatories: Livingston, LA and Hanford, WA X-ARM X-END STATION @ 4 km CORNER STATION CHILLER YARD LASER/VACUUM EQUIPMENT AREA (EXPERIMENTAL HALL) HVAC AIR HANDLING EQUIPMENT Y-ARM

4. LIGO-G070624-00-M LLNL Seminar 4 LIGO First Generation Detector Limiting noise floor  Interferometry is limited by three fundamental noise sources  seismic noise at the lowest frequencies  thermal noise (Brownian motion of mirror materials, suspensions) at intermediate frequencies  shot noise at high frequencies  Many other noise sources lie beneath and must be controlled as the instrument is improved

5. LIGO-G070624-00-M Building vibration requirements Broadband »Ground-transmitted: 2 x ambient seismic amplitude spectral density (LIGO Standard Spectrum – LSS) »Acoustic-induced: 1 x LSS Narrowband »< 2 x total rms motion in LSS from 0.1 – 1.0 Hz  2.8 x 10 -7 m »< 20 x total rms motion in LSS from 1.0 – 50 Hz  7 x 10 -8 m

6. LIGO-G070624-00-M Anthropogenic Seismic Signal Traced to Vitrification Plant Project, 10 km from X-end, up to 5000 workers expected during 5 year project E. Daw’s work R. Schofield, Environmental Disturbances; E5, E6 and E7 Investigations, LIGO-G020252-00

7. LIGO-G070624-00-M Soil Structure/Resonance Construction spectrum has shape of non- construction spectrum -- evidence for “ground resonance” of about 10 Hz

8. LIGO-G070624-00-M Wind Induced Seismic Noise High wind induced seismic motion on the 30 in. deep floor slab in the experimental hall »~5 times higher ASD »Increase in spectrum is broadly from ~0.3 to ~50 Hz, though mostly from ~0.4 to ~6 Hz »Wind at building 4 km (2.5 mi) distance was ~1/2 the speed (16 mph compared to 33 mph) Y-End Station Seismometer signal increase due to wind increase from 12 mph to 33 mph [R. Schofield, LHO electronic log, 1/11/2002 and LIGO-G020252-00]

9. LIGO-G070624-00-M Wind Histograms LIGO has difficulty locking it’s interferometers reliably when the wind exceeds 25 mph »~1% of the time in Louisiana »~10% of the time in Washington R. Schofield, Environmental Disturbances; E5, E6 and E7 Investigations, LIGO-G020252-00

10. LIGO-G070624-00-M Chiller isolation Chiller plant rotating equipment generates more vibrational energy than all other sources Placed Chiller plant at 300 ft from science instrument area based on available land and at this distance there isn’t a significant impact on chilled water line cost Predicted vibration transmission factor is 0.08 (measurement?) from chiller slab to technical slab Chiller equipment rotates at 60 Hz (3600 rpm) and weighs 21,400 lbs, mounted on a spring isolated skid Typically the foundation should be ~5 times the equipment weight to minimize vibrations Typical spring isolator frequencies are 4 to 5 Hz and give ~1% transmission If unbalance results in 0.1 g (realizable limit), then technical floor sees 80 micro-g @ 60 Hz or 6 nm

11. LIGO-G070624-00-M Rotating machinery Isolated fan skid (5 Hz vertical and horizontal), 29 to 31 Hz (1800 rpm) Six air handling fans operating at corner station with in-phase, unbalanced vibrations of 0.1 g (4 with 750 lb rotors, 2 with 550 lb rotors) One air handling fan operating with unbalanced vibration of 0.1 g ~15 nm horizontal and ~100 nm vertical motion on the mechanical room floor Significantly attenuation between the air handling unit foundation and the technical foundation due to separation

12. LIGO-G070624-00-M On-the-Instrument Vibration Sources? LIGO limits “noisy” operating equipment on the instrument and vacuum system to: »Ion pumps (no turbo-pumps) »LN2 Cryo-pump/dewar (no proximate pump and “infinite” capacity external tank) Predicted displacement spectra near Right End Station Optics Chamber (BSC9) caused by operation of Turbo-Pump TC6 (LIGO-C970091-00, Cambridge Acoustical Associates)

13. LIGO-G070624-00-M More Appropriate On-the-Instrument Noise Source for TMT The VLT Interferometer, B. Koehler, ESO, SMACS2 Symposium, 13-16 May 1997, Toulouse

14. LIGO-G070624-00-M LLNL Seminar 14 Vibration Isolation Systems »Reduce in-band seismic motion by 4 - 6 orders of magnitude »Large range actuation for initial alignment and drift compensation »Quiet actuation to correct for Earth tides and microseism at 0.15 Hz during observation

15. LIGO-G070624-00-M LLNL Seminar 15 Seismic Isolation – Springs and Masses damped spring cross section

16. LIGO-G070624-00-M LLNL Seminar 16 Seismic System Performance 10 2 10 0 10 - 2 10 - 4 10 - 6 10 - 8 10 -10 Horizontal Vertical 10 -6 HAM stack in air BSC stack in vacuum

17. LIGO-G070624-00-M Daily Variability of Seismic Noise PRE-ISOLATOR REQUIREMENT (95% of the time) Livingston Hanford RMS motion in 1-3 Hz band Displacement (m) day night

18. LIGO-G070624-00-M Hydraulic External Pre-Isolators (HEPI) Static load is supported by precision coil springs Bellows hydraulic pistons apply force without sliding friction, moving seals Laminar-flow differential valves control forces Working fluid is glycol/water formula (soluble, nonflammable) Stabilized “power supply” is remote hydraulic pump with “RC” filtering & pressure feedback control Fits in space now used for adjusters in existing system K. Mason, MIT

19. LIGO-G070624-00-M Active Seismic Isolation Hydraulic External Pre-Isolator (HEPI) BSC HYDRAULIC ACTUATOR ( HORIZONTAL ) OFFLOAD SPRINGS HYDRAULIC LINES & VALVES CROSSBEAM PIER BSC HAM

20. LIGO-G070624-00-M Active Seismic Isolation: How it Works Sensor correction extends isolation Low freq control with disp. sensor has typical benefits – improved linearity, hysteresis, since our sensors are better than our actuators Replace low freq crossover with blend To achieve isolation, feed information from STS-2 to correct the displacement sensor.

21. LIGO-G070624-00-M HEPI Preliminary Results LASTI performance: »Residual motions of 2e-9 m/√Hz at critical frequencies »Consistency of transmissibility and motion ratio indicates limits are loop gain and correction match »Exceeds requirements

22. LIGO-G070624-00-M LLNL Seminar 22 Core Optics Suspension and Control

23. LIGO-G070624-00-M LLNL Seminar 23 Core Optics Installation and Alignment Initial Alignment Requirement: 100 microradians (50 goal)

24. LIGO-G070624-00-M LLNL Seminar 24 What’s the Future for LIGO? Advanced LIGO Take advantage of new technologies and on-going R&D »Active anti-seismic system operating to lower frequencies »Lower thermal noise suspensions and optics »Higher laser power »More sensitive and more flexible optical configuration x10 better amplitude sensitivity  x1000 rate=(reach) 3  1 day of Advanced LIGO » 1 year of Initial LIGO ! Planned for FY2008 start, installation beginning 2011

25. LIGO-G070624-00-M LLNL Seminar 25 Astrophysical Targets for Advanced LIGO Neutron star & black hole binaries »inspiral »merger Spinning neutron stars »LMXBs »known pulsars »previously unknown Supernovae Stochastic background »Cosmological »Early universe

26. LIGO-G070624-00-M Render seismic noise a negligible limitation to GW searches »Both suspension and isolation systems contribute to attenuation »Newtonian background will dominate for frequencies less than ~15 Hz Reduce actuation forces on test masses Choose an active isolation approach: »3 stages of 6 degree-of- freedom each »Hydraulic External Pre-Isolation (HEPI) »Two Active Stages of Internal Seismic Isolation Increase number of passive isolation stages in suspensions »From single suspensions in initial LIGO to quadruple suspensions for Adv. LIGO Seismic Isolation Subsystem (SEI)

27. LIGO-G070624-00-M LLNL Seminar 27 Seismic isolation To open Advanced LIGO band at low frequencies, a complete redesign of the seismic isolation system is needed Active isolation, feed forward Required Isolation »10x @ 1 Hz »3000x @ 10 Hz Ground X Stage 1 X Stage 2 X goal

28. LIGO-G070624-00-M LLNL Seminar 28 Advanced LIGO suspensions Quad controls prototype installed at MIT and undergoing testing Noise prototype in fabrication »Lowest mode predicted @ 100 Hz Quad Noise Prototype