LASER INTERFEROMETER GRAVITATIONAL WAVE …



LASER INTERFEROMETER GRAVITATIONAL-WAVE OBSERVATORY

-LIGO-

CALIFORNIA INSTITUTE OF TECHNOLOGY

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

|Annual Report |

|AdL progress and plans; LASTI progress and plans |

| |

California Institute of Technology

LIGO Project – MS 51-33

Pasadena CA 91125

Phone (626) 395-2129

Fax (626) 304-9834

E-mail: mailto:info@ligo.caltech.edu

Massachusetts Institute of Technology

LIGO Project – MS 20B-145

Cambridge, MA 01239

Phone (617) 253-4824

Fax (617) 253-7014

E-mail: mailto:info@ligo.mit.edu

PROJECT SUMMARY

TABLE OF CONTENTS

A. PROJECT SUMMARY 2

B. TABLE OF CONTENTS 3

C. PROJECT DESCRIPTION 4

C.1. Work Accomplished During FY 2003 4

C.1.1. LIGO Hanford Observatory 4

C.1.2. LIGO Livingston Observatory 5

C.1.3. Educational Outreach 7

C.1.4. Safety 8

C.1.5. Technical and Engineering Support 8

C.1.6. Detector Support 8

C.1.7. Data and Computing Group 11

C.1.8. Campus Research Facilities 15

C.1.9. Advanced R&D 17

C.1.10. LIGO Scientific Collaboration (LSC) 23

C.1.11. Astrophysics and Data Analysis 24

C.1.12. Actual Costs, Staffing, Organization 28

C.2. Work Planned for FY 2004 32

C.2.1. Operations 32

C.2.2. Detector Commissioning Goals 32

C.2.3. Modeling and Simulation 33

C.2.4. LIGO Data Analysis System (LDAS) 33

C.2.5. Information Technology Support Group 34

C.2.6. Campus Research Facilities 34

C.2.7. Advanced R&D 35

C.2.8. LIGO Scientific Collaboration 35

C.2.9. Astrophysics and Data Analysis 36

C.2.10. FY 2004 Meetings 37

D. References 38

F. PROPOSAL BUDGET JUSTIFICATION 39

F.1. Summary 39

F.2. MIT Funding 39

F.3. Proposal Budgets 39

F.3.1. Line A—Senior Personnel 44

F.3.2. Line B—Salaries and Wages 44

F.3.3. Line C—Fringe Benefits 44

F.3.4. Line D—Equipment 45

F.3.5. Line F—Participant Costs 46

F.3.6. Line G5—Other Direct Costs, Subawards 46

F.3.7. Line G6—Other Direct Costs, Other (GRA Benefits, Subcontracts) 46

F.3.8. Line I—Indirect Costs 47

Appendix A. 48

Appendix B. 49

PROJECT DESCRIPTION

1 MIT Facilities (LASTI)

The goal of the MIT LASTI facility is to support the development and testing of a range of LIGO subsystems and components at full scale in an environment that is as close to that found at the observatories as possible. The present principal use of this facility is for the testing of the External Pre-Isolator (EPI) system currently being implemented at the LIGO Livingston Observatory to alleviate the problems caused by excessive seismic noise due to logging in the area.

The development of the EPI has been the focus of the LASTI group for the last two years. This year’s efforts have been devoted to learning optimal methods for the control of the system. In addition to this a considerable amount of LASTI manpower has been spent on transferring the lessons learned at LASTI during the EPI tests to the local staff at Livingston Observatory. This significantly contributed to the efficient implementation of the system at the LIGO Livingston Observatory. This has involved many of the LASTI personnel spending considerable time amounts of time at the site.

The LASTI personnel also contributed to the design, installation and commissioning of a Thermal Compensation System (TCS). This system has been incorporated into the LIGO Hanford 4km detector. The TCS allows distortions in the transmission profile of the Input Test Masses (ITMs) caused by excessive 1.064 um power absorption to be corrected.

The 10 Watt PSL system at LASTI was used in the development of new frequency stabilization and intensity stabilization servos that will be implemented at the sites sometime before the S4 science run.

In the Advanced LIGO system it will be necessary to mount geophones and photo-detectors on the seismic isolation platforms within the high vacuum envelope. Obviously these components will need to be ultra-high vacuum compatible. With this in mind we designed and build a vacuum compatible geophone. This consisted of placing a regular geophone inside a stainless steel vacuum vessel that was filled with a neon buffer gas. The outside of these containers is ultra high vacuum compatible and the neon buffer gas enables the detection of any significant leaks. These vacuum compatible geophones are now routinely used inside the LASTI vacuum system.

With the completion of the HEPI testing of LASTI we are now able to use the HEPI system as a tool. This will be utilized later in 2004 when we will characterize a prototype triple suspension in one of our vacuum chambers. The HEPI system will then be used as a shake table to study the dynamics of the triple under the effects of ground excitation. In addition to this installation and alignment procedures will be learned that will reduce the installation time for Advanced LIGO at the sites.

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2 Advanced R&D

This year we initiated or continued a broad range of research to support the development of advanced detectors. This effort is very strongly collaborative, and the research highlights described below are often the result of collaborations with other institutions in the LIGO Scientific Collaboration (LSC). The results confirm the basic Advanced LIGO Design, and have allowed us to further refine and detail the subsystem designs.

1 Systems and Interferometer Sensing and Control

The Systems group supported the development of more detailed requirements for a number of subsystems, including the Core Optics, Suspensions, and Isolation subsystems. The detailed optical layout of the interferometer has proceeded as a tool to ensure interface compatibility and to establish ‘footprints’ and allowed volumes for in-vacuum subsystems.

The Interferometer Sensing and Control subsystem met a milestone in selecting a DC readout for the gravitational wave signal rather than the traditional modulation-demodulation system. This was enabled by a quantum-mechanical analysis (REF ) of the readout indicating that this system will deliver the best sensitivity, and associcated work showing that this is also the easiest to implement.

2 Seismic Isolation

The seismic isolation team continued to focus on pre-isolator research for Initial LIGO. As reported above, the development of this element of Advanced LIGO was accelerated to be applied to reduce the excess seismic noise at the Livingston Observatory. In addition to supporting the fabrication and installation of the pre-isolator at the observatory, the prototype and first-article units at the MIT LASTI testbed were exploited to characterize the mechanical system, develop and test servo control laws, and to write software routines for the operation, test, and safety aspects of the real-time controllers. Sample performance at an intermediate state of commissioning is shown in Figure X, showing the fulfillment of the basic requirements of a factor of 10 suppression in the critical region between 1-3 Hz. Innovative work in adaptive feed-forward schemes have been shown to give superior performance to traditional fixed-gain systems, and may be integrated into the Observatory controls when ready.

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Figure 1: Performance of HEPI external pre-isolator in commissioning at the MIT LASTI facility.

The seismic isolation Technology Demonstrator, designed by the LSU-Stanford-LIGO team, fabricated by the LIGO Laboratory, and installed in the Stanford Engineering Test Facility, has delivered valuable results. A photograph of the installed system is shown in Figure X. It has allowed detailed requirements on geometry and dynamics to be delivered to the designers of the final prototypes, and control topologies have been tested to optimize the performance for the sensors and actuators in the system. Some early results are shown in Figure X; each stage will supply roughly a factor of 30 suppression over a frequency range from ~2 - ~20 Hz, which with the external pre-isolator and suspension meets the requirement for suppression of seismic motion for Advanced LIGO.

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Figure 2: Figure 5. Picture of the Advanced LIGO seismic isolation technology demonstrator two-stage active platform inside the vacuum tank. The two stages are structurally interleaved to correctly position the centers of gravity. One of the 3 STS-2 seismometers mounted on the first stage, and one of the Geotech GS-13 geophones mounted on stage two are indicated. The overall width is approximately 1.5 m. Masses simulating the load of the suspension system can be seen on the optics table which is part of stage two of the platform.

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Figure 3: Measurements from the technology demonstrator prototype active isolation platform at Stanford, indicating the desired suppression of a factor of 30 in one axis of one stage. The heavy black curve shows the displacement noise level on the ground in a horizontal direction and the dotted curve the residual noise on stage 1 of the platform. The blend frequency used for these measurements was 0.5 Hz. The feature seen at around 25 Hz is believed to be a resonance of the current support structure.

.Based on the encouraging results and detailed information from these prototypes, a contract has been let with ASI for the design of the Advanced LIGO seismic isolation in-vacuum platform, as well as for the fabrication of a test-mass version of the isolator. The delivery date for this isolator is November 2004, when it will be installed at the MIT LASTI facility for standalone testing and subsequent integration with a test-mass suspension.

3 Suspensions

The suspension design for Advanced LIGO is based on developments by the Glasgow UK GEO group for the GEO 600 detector, and the effort remains a close collaboration of scientists from Glasgow, Stanford, and the LIGO Laboratory. Two suspension designs received considerable attention this year. The triple pendulum prototype suspension for auxiliary optics was characterized, and models refined to correctly reflect experimental measurements. The modes of the system were damped, and various actuator and control loops were developed. The suspension was sent from Caltech, where it had been fabricated and assembled, to MIT, where it was installed in the MIT LASTI testbed. This allowed exercise of installation tooling and procedures, and precision mechanical alignment with the metrology tools used for initial LIGO. It is undergoing further characterization at MIT, using the HEPI system there as a ‘shake table’ for measurement of transfer functions.

Work continued in Glasgow, Stanford, and Caltech on the test-mass quadruple suspension design. Fabrication techniques for the fused-silica suspension ribbons and attachments were refined in Glasgow, and detailed designs and finite-element models were pursued at Caltech. An overall sketch from this on-going design effort, and a solid-model rendering, are shown in Figure X.

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Figure 4: Schematic diagram of quadruple pendulum suspension system for Advanced LIGO. A face view of the main chain is shown on the left, and in the middle is shown a side view with main and reaction chains visible. On the right is a conceptual design for the supporting structure which is approximately 2 m in height, and whose top surface would be rigidly attached to the optics table. This structure would support elements of the sensor and actuators for local control, and earthquake stops to restrict motion of the masses and support them in the event of a wire or ribbon failure.

4 Optics

The requirements and conceptual design for the optics subsystem were documented and brought to a successful Design Requirements Review in January 2004. Requirements for both the baseline sapphire substrate material and the fused silica alternative were addressed.

Considerable effort has gone into the background research and fact-gathering for the selection of the substrate for continued development. Studies pursued by the Glasgow-Stanford-LIGO team include polishing, annealing (to address mechanical loss in fused silica and optical loss in sapphire), mechanical loss (‘Q’) measurements, scatter characterization, as well as thermal modeling. Direct measurement of thermal noise was performed in the TNI (see below). A recommendation to the LIGO Laboratory Directorate and LSC for the choice of substrate is planned to take place this year to support the further development of suspensions in the US and UK.

The Thermal Noise Interferometer (TNI) research at Caltech produced several very interesting results this year. This special-purpose interferometer is designed to demonstrate our understanding of thermal noise in substrates and coatings by magnifying the effects (using small optical spot sized on the substrates) and suppressing other noise sources (with a short baseline and common-mode seismic excitation).

In the first result, fused silica substrates with typical optical coatings were used. After considerable effort to reduce spurious electronic noise sources, a region of noise which appears to be limited only by thermal noise from ~500 Hz to ~10 kHz was exposed (see Figure X). A model for the substrate and coating thermal noise is effectively in agreement with the observed form and level of noise using model values consistent with other measurements. This confirms, and extends to lower more interesting noise levels, an earlier measurement by our Japanese TAMA colleagues (Numata, et al., PRL 91 (26), 260602 (Dec. 31, 2003)), and gives us considerable comfort that our independent measurements of mechanical losses in coatings can be used to predict thermal noise levels in interferometers, both initial and Advanced.

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Figure 5: Thermal Noise Interferometer results, indicating that the thermal noise level in fused silica substrates with conventional optical coatings behaves as anticipated. The coating mechanical loss from this experiment is ~1.5x10^-4.

In the second result, the fused silica substrates were removed and replaced with sapphire substrates. For this substrate, the thermal expansion and contraction due to thermal fluctuations in the substrate are expected to dominate in the gravitational wave band. Using materials parameters measured in earlier work at MIT and elsewhere, the observed level agrees quite well with the observed level. Again, this gives us confirmation of a central element in the noise budget of Advanced LIGO and allows us to move forward with our substrate recommendation with confidence.

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Figure 6: Thermal Noise Interferometer results with sapphire substrates. The thermoelastic noise is seen, consistent with models, between ~500 Hz and ~10 kHz.

5 Optical Coatings

Both the (familiar) optical losses but also the mechanical loss in optical coatings are important to the performance to Advanced LIGO. The challenge for Advanced LIGO lies in achieving the required low mechanical loss that is needed to control the thermal noise perceived by the interferometer. We have put into place contracts with two state-of-the-art coating firms (VIRGO SMA, Lyon, France; CSIRO, Sydney, Australia) to help us understand the sources of loss and to develop low mechanical loss coatings. Along with our LSC Collaborators (Stanford and Glasgow), we have a combination of academic and practical expertise to address the questions. This year trial coatings were made by both coating firms to establish a baseline, and some doping and annealing processes were explored. To date the losses have been reduced by small increments, but in a way consistent with the theories of losses in the Tantala, and are encouraging for further reductions.

6 Pre-stabilized Laser and Input Optics

The baseline approach to producing the Advanced LIGO laser met an important milestone at the development lab in the Max Planck AEI Hannover (Germany). This end-pumped Nd:YAG rod laser, set up as a free-running butterfly cavity, produced 213 W with an M^2 of 1.15. This meets the requirements for power, and may have met the beam quality requirement as well (this must await single-mode operation). Work continued on alternative designs at Stanford and Adelaide.

Within the LIGO Laboratory, progress was made on setting the performance requirements for the laser, and refining the intensity stabilization. Final measurements were made on the prototype setup at MIT for developing this control system, and a student completed his thesis on the topic (Jameson Rollins). The result, shown in Figure X, indicates that the requirement is met for frequencies above 40 Hz. The limit to the performance is thought to be residual beam jitter due to the air path for the laser beam; the design (and the next stage of prototyping) calls for an all-in-vacuum sensing system which will sidestep this difficulty.

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Figure 7: Performance of the prototype Advanced LIGO Intensity stabilization system. The red curve indicates the performance to date; the black curve represents the requirement.

The Input Optics are the responsibility of the University of Florida for Advanced LIGO (as they were for initial LIGO). Development of high-power Faraday Isolators and Modulators have been a focus for them. The LIGO Lab’s participation is at the LIGO Livingston Laboratory, where postdocs shared with Florida have set up a high-power testing laboratory. We have been searching for a vendor of a 100W class laser for ‘stress testing’ of the components, and have recently taken delivery of a fiber laser (from IPG Photonics) which is just now undergoing characterization and qualification.

7 Thermal Compensation

The lens formed in the substrates due to the absorption of the laser light in the substrate make the interferometer optical system sensitive to the power level. We wish to have a system which can work at all power levels, and so will apply complementary heat to the substrates to bring the curvature to the correct value for all input powers. For Advanced LIGO, most of the recent work has been in the modeling of the system, using both the mode-based MELODY model (developed by our Stanford collaborators) and the FFT-based Huygens propagation numerical code (developed at MIT for initial LIGO and now exercised at Caltech). As reported elsewhere, the basic ideas of thermal compensation have been applied to initial LIGO, and the Advanced LIGO team has been central in that application. Not surprisingly, the creative process and testing in situ have helped the Advanced LIGO design progress as well .Interface issues with the Core Optics and the Suspensions teams have been resolved, with simplification of the overall interferometer design.

2 Work Planned for FY 2004

1 Campus Research Facilities

1 MIT Facilities (LASTI)

In the winter of 2004 we will take delivery of the first prototype of the Advanced LIGO Seismic Isolation system for a BSC chamber. The first part of next year will be spent learning how install and optimally control this system. It is also planned that a prototype of the Advanced LIGO quad pendulum design will also be delivered. This quad pendulum design is the planned suspension for the core optics. This will enable us to demonstrate for the first time in LIGO the cartridge installation technique. It is thought that this technique will help to minimize the downtime between initial LIGO and Advanced LIGO. In addition to this we will be able to check for unforeseen interactions between the Advanced LIGO Seismic Isolation and Suspension systems.

2 Advanced R&D

The R&D program will continue to focus on the Advanced LIGO subsystems, the establishment of detailed requirements, and the preliminary design phases. Significant activities planned for FY2005 include the following:

• Seismic Isolation: Stanford Engineering Test Facility (ETF) testing will be further exploited. A set of software for the control systems and the supervisory control will be delivered for system testing at MIT LASTI. The test-mass (‘BSC’) in-vacuum prototype will be installed at LASTI and commissioned.

• Suspensions: The UK team, working with the LIGO team, will complete the design for the test mass suspension. The first ‘controls’ quadruple suspension will be built at Caltech and delivered to LASTI. It will be integrated with the seismic isolation prototype, and the combined system characterized.

• Optics: The full-size substrates to be used in LASTI system testing will complete their pathfinder process: they will be polished and coated, and prepared for attachment to the suspension. Tests of thermal compensation in a suspended cavity, performed at the Australian Gingin facility in collaboration with LIGO, will be completed. Design and prototyping of the Input Optics (in collaboration with the University of Florida), and the Auxiliary Optics, will continue.

• Lasers: The formal requirements review and documentation for the complete Pre-Stabilized Laser will be completed, and prototyping of the system will continue at the University of Hannover.

• Systems: We will continue to refine the baseline optical layout and interface documentation. The end-to-end simulation tool, developed for Initial LIGO, will be used to simulate locking of the complete Advanced LIGO and to study the consequences of the stored power in the optical cavities and their influence on the longitudinal and angular controls.

Appendix A.

Anticipated, Near-Term, Major LIGO Procurements

This list summarizes our current estimates concerning the size and scheduling of near-term significant LIGO procurements and whether or not NSF review and approval will be required. Where the fund source is FY 2003, these are procurements in process under the funding already approved by the Cooperative Agreement.

TBD FOR ADL

Appendix B.

MIT Proposal Budget for FY 2004 Participation in LIGO

The original signed MIT Proposal including budget allocations is retained on file at Caltech.

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