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. Specific Advanced LIGO Program Tasks (‘01 - ‘06+):
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. Laboratory and LSC Visitors (to date)
LASTI People
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…
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
LSC Meeting August ‘03

5. LASTI Advanced LIGO R&D Program
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
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
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 = kg
ETM Suspension mass = 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
-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