L IGO A DVANCED S YSTEMS T EST I NTERFEROMETER ( LASTI )

1. LIGO ADVANCED SYSTEMS TEST INTERFEROMETER (LASTI) Program Update: LSC Meeting, Hannover Dave Ottaway August 2003 LSC Meeting August ‘03

2. Talk Overview • LASTI goals and timelines • Overview of progress to date • Previously proposed solution, new problems • Proposed solutions • Conclusions LSC Meeting August ‘03

3. LASTI Mission • Test LIGO components & systems at full mechanical scale • Practice installation & commissioning • Minimize delays & downtime for advanced LIGO upgrades • Qualify design mods & retrofits for initial LIGO Specific Advanced LIGO Program Tasks (‘01 - ‘06+): • Qualify advanced isolation & suspension systems and associated controls at full scale • Develop detailed SEI/SUS installation & commissioning handbook • Look for unforeseen interactions & excess displacement noise • Test PSL and Input Mode Cleaner together at full power LSC Meeting August ‘03

4. Resident MIT Staff Students - Jamie Rollins, Stefan Ballmer, Dan Mason, Waseem Bakr Engineering - Myron MacInnis, Ken Mason, Jonathan Allen, Bill Rankin Scientists - Gregg Harry, Rich Mittleman, Dave Ottaway, David Shoemaker, Pradeep Sarin, Mike Zucker (Advice) Computers – Keith Bayer Laboratory and LSC Visitors (to date) Initial SEI & SUS- Corey Gray, Hugh Radkins, Gary Traylor, Harry Overmier, Betsy Bland , Jonathan Kern, Marcel Hammond, Dennis Coyne… Advanced SEI - Joe Giaime, Brian Lantz, Wensheng Hua, Corwin Hardham… Advanced SUS - Norna Robertson, Calum Torrie, Janeen Romie, Phil Willems, Justin Greenhalgh, Ken Strain, Caroline Cantley, Mark Barton… CDS/DAQ - Jay Heefner, Rus Wooley, Paul Russel… LASTI People LSC Meeting August ‘03

5. Commission infrastructure (vacuum, cleanrooms, cranes…) Commission PSL & controls Commission initial seismic stack, suspensions & 1m test cavity in HAM chamber Develop & test EPI for LLO seismic remediation Qualification test of early pre-prototype triple pendulum (Delayed) Integrate/test active HAM SEI pathfinder (Delayed) Integrate/test active BSC SEI pathfinder (Delayed) Integrate/test Quad and Triple suspensions Integrate/test sapphire & fused silica core optics Qualify for low displacement noise with sensitive interferometer system Integrate and test full scale adaptive thermal compensation Integrate/test AdLIGO 180 Watt PSL & Mode Cleaner LASTI Advanced LIGO R&D Program LSC Meeting August ‘03

6. High Bay Schematic Y-end HAM X-end HAM BSC Y-mid HAM PSL • Currently planned to use the Y-arm • More space around the X-arm • BSC orientated such that layout mimics: • ETM Chamber – X arm, ITM Chamber – Y arm • Y mid with seismic isolation installed is not compatible for additional experiments if Y-end HAM is used for LASTI LSC Meeting August ‘03

7. LASTI Infrastructure and PSL LASTI PSL BSC chamber including cartridge clean room Mid Y HAM with MEPI LSC Meeting August ‘03

8. Pre-stabilized Laser (PSL) J. Rollins aligning PMC cavity D. Ottaway and J. Rollins commissioning controls LSC Meeting August ‘03

9. Intensity Stabilization Experiment Our approach: => Very low noise AC-coupled PD => Low voltage low noise parts in the signal path => Beam geometry stabilized by PMC LSC Meeting August ‘03

10. High Bandwidth FSS Servo Design • Alternative high bandwidth frequency topology tried • Achieved an upper unity gain frequency of 1 MHz • Based on design by J. Hall LSC Meeting August ‘03

11. External Pre-Isolators (EPI) K. Mason, MIT LSC Meeting August ‘03

12. External Pre-Isolators (EPI) • Active vibration suppression interposed between ground and existing internal seismic isolation • Main gravitational load is supported by angled coil springs (2 per leg) • 2 forcers per leg, one vertical and one tangential • Payload-mounted L-4C geophone + DC position sensor for local feedback • STS-2 seismometer on floor permits feedforward at low frequencies (mseism) J. Giaime, LLO/LSU LSC Meeting August ‘03

13. Initially proposed Interferometric Noise Test Configuration 16 m ETM RM ITM RM MC3 MC2 MC1 MCx, MMTx, SM: Adv LIGO SOS ETM, ITM: Adv LIGO LOS PSL LSC Meeting August ‘03

14. LASTI Interferometer Sensitivity Model • For sapphire TM’s (baseline plan) • QTM= 2e8, Fcoating= 4e-4 • 6W laser power (LIGO I laser) • Cavity finesse 2000 • 16m cavity length • 3mm beam radius (max. practical) • Limited by thermoelastic noise over most of band due to small beam G. Harry, 6/25/02 LSC Meeting August ‘03

15. (Silica Test Mass Option) • For silica TM’s (backup plan) • QTM= 3e7, Fcoating= 4e-4 • 6W laser power (LIGO I laser) • Cavity finesse 2000 • 15m cavity length • 2.25mm beam radius • Limited by internal Brownian noise over most of band due to lower Q G. Harry, 6/25/02 LSC Meeting August ‘03

16. Summary of Initial Solution • Two cavities proposed to provide common mode rejection of mode cleaner frequency noise and technical radiation pressure noise • Problem : Proposed payload exceeds seismic limits • Seismic mass limit = 800 kg • Current payload mass ~ 1000 kg • ITM Suspension mass = 422.5 kg • ETM Suspension mass = 472.5 kg • MC Suspension mass = 81.3 kg +spacer • Possible solutions : Modify seismic for LASTI • or modify/remove one of the reference cavities • or anchor mirror catchers elsewhere LSC Meeting August ‘03

17. Active Seismic Isolation LSC Meeting August ‘03

18. Advanced LIGO Suspensions • Based on successful GEO600 triple pendulum design • Quad pendula for TM, BS; Triples for input optics • Blade springs for vertical isolation • Indirect damping through upper stage recoil • Electrostatic or photon drive for fast control at final stage; reaction mass for ES recoil LSC Meeting August ‘03 R. Jones, Glasgow U.

19. More details of possible solutions • Designing higher payload LASTI Seismic => Specifically testing Seismic then re-engineering to hold larger suspension weight Cons -Expensive, time consuming -Almost certainly better ways • Anchoring catcher to vacuum chamber Cons -Not likely to be used in AdvLIGO, and hence not testing what is in Advanced LIGO Pros -Saves a lot of weight -No modifications necessary to LASTI Seismic LSC Meeting August ‘03

20. More details of possible solutions • Using a single test cavity • Mass closest to designed AdvLIGO seismic load • Simplest design • Potentially good performance if OSEM noise in MC can be overcome • Also possible if global control can be used to damp the MC • Alternatively turn damping off for short periods • Using a second lighter cavity test cavity • Possible solution if OSEM noise in MC cavity cannot be fixed • Disable local damping rely on global control for damping • Control problems and noise analysis to still needs to be done ! LSC Meeting August ‘03

21. Parameter File for Calculations Mode Cleaner Parameters Length = 16 m Finesse = 2026 Modulation frequency = 25 MHz Laser power = 0.3 W (Low Power) = 1.5 W (High Power) MC1,MC3 ROC = Flat MC2 ROC = 26.9 m Spotsize = 2.7 mm Coating phi = 5.0e-5 Substrate phi = 0.3e-7 Substrate mass =3 kg Test Cavity Parameters Length =16m Finesse = 2026 Modulation frequency = 9.8 MHz PD quantum efficiency = 0.9 Laser Power = 0.3 W (Low Power) = 1.5 W (High Power) Spot size = 3mm (Conservative) = 16 mm (Aggressive) Coating phi =5.0e-5 Input mirror substrate: Fused Silica Substrate phi = 1.0e-7 Substrate mass =15 kg Input mirror ROC = Flat (Aggressive) = 40 m (Conservative) End mirror substrate: Sapphire Substrate phi = 1.0e-8 Substrate mass = 40 kg Output mirror ROC = 40 km General Parameters Intensity noise =Advanced LIGO Requirements Beam Jitter = LIGO 1 Measured PSL filtered by MC LSC Meeting August ‘03

22. Predicted MC Operation • Beam jitter only known 100 Hz • Calculated using AdvLIGO Parameters • High power curve ignores VCO, beam jitter noise • Relies on alternative OSEM strategy LSC Meeting August ‘03

23. Predicted Single Arm LASTI Performance (Low Power) • Power incident on mode cleaner =0.3 W • Conservative LASTI not limited by MC noise • Requires significant improvement over OSEM damping • Should be possible with eddy current damping LSC Meeting August ‘03

24. Predicted Single Arm LASTI Performance (Higher Power) • Power incident on mode cleaner =1.5 W • Can reach AdvLIGO sensitivity at 1kHz if technical intensity noise is improved from 2e-6 to 5e-7 at 1kHz LSC Meeting August ‘03

25. Comments on Aggressive LASTI • Parameters used: • Cavity length = 16 m • Input mirror roc =flat, Output mirror roc =40 km • Spot size = 16 mm • Alignment sensitivity 3e-7 radians for 1% power loss • Beam jitter not likely to be a problem based on static mis-alignment of 3e-7 radians and dynamic beam jitter limited by current PSL. Ref E. Calloni et al. Optics Communications 142 (1997) 50-54 LSC Meeting August ‘03

26. Updated milestones:LLO seismic remediation interleaved with Advanced LIGO development • 4Q99 (4Q99 act): LASTI vacuum envelope commissioned √ • 1Q00sch (3Q01 act): LASTI SEI external structures installed √ • 2Q00sch (4Q00 act): LASTI infrastructure design review √ • 3Q01sch (1Q02 act): LASTI infrastructure complete (DAQ, SEI, PSL, test cavity) √ • NEW 4Q01: Fit LIGO I BSC stack (from spare parts) to support EPI qualification √ • NEW 1Q02: External pre-isolator tests for LLO seismic retrofit underway • NEW 4Q02: PSL intensity stabilization experiment underway • NEW 4Q02: MC triple suspension prototype installed for “controls” pre-test • 4Q02: HAM SEI pathfinder installed for standalone testing (slips to 3Q04) • 3Q02: BSC SEI pathfinder installed for standalone testing (slips to 3Q04) • 2Q04: LASTI noise test begins; SUS prototypes installed (slips to 2Q05) • NEW: 2Q05: Thermal compensation integration and test • 4Q05: Interferometric displacement tests • 1Q06: LASTI SUS/SEI test review • 2Q06: Adv LIGO PSL/MC tests start (180 Watts) LSC Meeting August ‘03

27. Short term plans (ie 6months) • Finalize the design of the LASTI experiment for Advanced LIGO • EPI • Test HEPI on a HAM • Finish conversion of controls from Dspace to VME • Install a controls prototype in the Xend HAM LSC Meeting August ‘03

28. Conclusions • LASTI’s mission to pre-qualify Advanced LIGO technology has an unexpected dress rehearsal in the LLO seismic retrofit with the successful trial of HEPI/MEPI • Need to find more information about MC suspensions before final decision can be made on the Advanced LIGO experimental program • If mode cleaner suspension noise is significantly better than the radiation pressure limited Advanced LIGO specification can probably only require a single test cavity • It may be technically feasible to significantly increase the spot size in the test cavity and measure noise at the Advanced LIGO displacement sensitivity (Not 10 X below) at 10 Hz and 1kHz LSC Meeting August ‘03