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Overview of Advanced LIGO

Overview of Advanced LIGO. David Shoemaker PAC meeting, NSF Review 5 June 2003, 11 June 2003. Advanced LIGO. LIGO mission: detect gravitational waves and initiate GW astronomy Next detector Must be of significance for astrophysics

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Overview of Advanced LIGO

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  1. Overview of Advanced LIGO David Shoemaker PAC meeting, NSF Review 5 June 2003, 11 June 2003 LIGO Laboratory

  2. Advanced LIGO • LIGO mission: detect gravitational waves and initiate GW astronomy • Next detector • Must be of significance for astrophysics • Should be at the limits of reasonable extrapolations of detector physics and technologies • Should lead to a realizable, practical, reliable instrument • Should come into existence neither too early nor too late Advanced LIGO LIGO Laboratory

  3. Initial and Advanced LIGO • Factor 10 higher amplitude sensitivity • (Reach)3 = rate • Factor 4 lower frequency bound • Binary inspirals • Stochastic background • Tunable response • Periodic sources • Broad-band bursts LIGO Laboratory

  4. Design features 40 KG SAPPHIRETEST MASSES ACTIVE ISOLATION QUAD SILICASUSPENSION 200 W LASER,MODULATION SYSTEM PRM Power Recycling Mirror BS Beam Splitter ITM Input Test Mass ETM End Test Mass SRM Signal Recycling Mirror PD Photodiode LIGO Laboratory

  5. Comparison of key parameters LIGO Laboratory

  6. Design ‘signature’ • Low-frequency ‘brick wall’ from Newtownian background • Time-varying distribution of mass near test masses • Limit for ground-based interferometers • Isolation system renders seismic noise negligible at all frequencies • Thermal noise • Low-mechanical loss materials and assembly techniques • Monolithic fused-silica suspensions • Sapphire (baseline) test masses • Quantum noise • Greatest laser powers allowed by present materials; best use of that light • Fabry-Perot arm, signal-recycled Michelson • Allows optimization for astrophysics and instrumental limitations • Advanced LIGO's Fabry-Perot Michelson IFO is a platform for all currently envisaged enhancements to this detector architecture LIGO Laboratory

  7. Anatomy of the projected Adv LIGO detector performance • Newtonian background,estimate for LIGO sites • Seismic ‘cutoff’ at 10 Hz • Suspension thermal noise • Test mass thermal noise • Unified quantum noise dominates at most frequencies for fullpower, broadband tuning Initial LIGO 10-22 10-23 10-24 10-25 1 kHz 100 Hz 10 Hz LIGO Laboratory

  8. Scope of proposal • Upgrade of the detector • All interferometer subsystems • Data acquisition and control infrastructure • Upgrade of the laboratory data analysis system • Observatory on-line analysis • Caltech and MIT campus off-line analysis and archive • Virtually no changes in the infrastructure • Buildings, foundations, services, 4km arms unchanged • Move 2km test mass chambers to 4km point at Hanford • Replacement of ~15m long spool piece in vacuum equipment • Present vacuum quality suffices for Advanced LIGO LIGO Laboratory

  9. Baseline plan • Initial LIGO Observation 2002 – 2006 • 1+ year observation within LIGO Observatory • Significant networked observation with GEO, VIRGO, TAMA • Structured R&D program to develop technologies • Conceptual design developed by LSC in 1998 • Cooperative Agreement carries R&D to Final Design, 2005 • Proposal early 2003 for fabrication, installation • Long-lead purchases planned for 2004, real start 2005 • Sapphire Test Mass material, seismic isolation fabrication • Prepare a ‘stock’ of equipment for minimum downtime, rapid installation • Start installation in 2007 • Baseline is a staggered installation, Livingston and then Hanford • Coincident observations by 2010 LIGO Laboratory

  10. Reference design options • Baseline is upgrade of 3 interferometers • in discovery phase, 3rd IFO serves to improve statistics (nongaussian noise), • improvement of sensitivity (roughly double event rate for 3 instead of 2 identical interferometers), • quiet commissioning on second LHO IFO while observing with the LHO-LLO pair • allow better stochastic upper limits (co-located instruments) • potentially increase uptime in early phases of commissioning/observation • In observation phase, the same IFO configuration can be tuned to increase low or high frequency sensitivity • sub-micron shift in the operating point of one mirror suffices • an optimization would require a change in signal recycling mirror transmission • could decide before commissioning, or after a period of observation • third IFO could e.g., • observe with a narrow-band VIRGO • focus alone on a known-frequency periodic source • focus on a coalescence or BH-ringing frequency of an inspiral detected by other two IFOs LIGO Laboratory

  11. Reference design options • Baseline is to upgrade the 3rd interferometer from 2km to 4km • Could leave at 2km • Cost is modest and sensitivity gain supports discovery • Will certainly want maximum sensitivity later • Baseline is effectively a simultaneous upgrade of both sites • Could stagger quite significantly to maintain the network – with an equally significant delay in completion and coincidence observations by the two LIGO sites • Baseline is to employ Sapphire as the test mass material • Fused silica an interesting fallback – more later LIGO Laboratory

  12. Potential later incremental upgrades • Available as options in the future to fully exploit the Advanced LIGO platform • To address… • Low-frequency ‘brick wall’ from Newtownian background • Regression techniques based on a seismometer grid may allow ~factor 10 reduction (shift down ~0.75 in frequency of ‘brick wall’) • Thermal noise • Non-Gaussian ‘Top Hat’ beams in arms may lead to a significant reduction in thermoelastic noise contribution • Interferometer topology • Injecting ‘squeezed vacuum’ may allow broader sensitive region • Variable transmission signal recycling mirror could allow optimization of Q and frequency of narrow-band mode • Reference Design is well defined, does not include the above LIGO Laboratory

  13. Timing of Advanced LIGO • Observation of gravitational waves is a compelling scientific goal, and Advanced LIGO will be a crucial element • to detection if none made with initial LIGO • to capitalizing on the science if a detection is made with initial LIGO • Delaying Advanced LIGO likely to create a significant gap in the field – at least in the US • Encouragement from both instrument and astrophysics communities • Our LSC-wide R&D program is in concerted motion • Appears possible to meet program goals • We are reasonably well prepared • Reference design well established, largely confirmed through R&D • Timely for International partners that we move forward now LIGO Laboratory

  14. Advanced LIGO • An exciting and significant step forward from first generation • instruments • potential for astrophysics • No fundamental surprises as we move forward; concept and realization remain intact with adiabatic changes • A great deal of momentum and real progress in every subsystem • Thorne: Astrophysics with Advanced LIGO • Fritschel: Systems, sensing, optics subsystems • Coyne: Mechanical subsystems, electronics, installation • Sanders: Cost and Schedule overview LIGO Laboratory

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