Purpose and Scope
This document outlines the engineering and implementation requirements that are applicable to all Advanced LIGO Suspension systems It focuses specifically on general engineering requirements for the Suspension Subsystem (SUS), excluding performance criteria.
Applicable Documents
• E960022, LIGO Vacuum Compatibility, Cleaning Methods and Qualification Procedures
• E960050, LIGO Vacuum Compatible Materials List
• E010613, Generic Requirements and Standards for Detector Systems
• E030513, LASTI Prototype Suspension Controller Operation Manual
• E030518, Mode Cleaner Triple Suspension Assembly Specification
• E030546, Suspension Controls Prototype Test Plan
• E030647, Advanced LIGO Detector Subsystem Interface Control Document
• E040329, Advanced LIGO Quadruple Pendulum Suspension Failure Modes and Subsequent Repair Approaches
• M950090, "Guidelines for Detector Construction Activities", M950090
• M980140, LIGO Hanford Observatory Emergency Action Plan
• M990034, LIGO Hanford Observatory Contamination Control Plan
• M990148, LIGO Livingston Observatory Laser Safety Plan
• M990184, LIGO Livingston Observatory Emergency Action Plan
• M000009, LIGO Livingston Observatory Security Procedures
• M020131, LIGO Hanford Observatory Laser Safety Plan with Added Engineering Controls and Interlock Hardware
• M040088, RODA on OSEM Counts and Responsibilities for SUS Prototypes
• M040091, RODA on Covers for Advanced LIGO Optics
• M040112, LIGO Livingston Laser Safety Plan
• M050174, RODA on Requirement for SUS Features to Aid in Initial Alignment
• M050175, RODA on Initial Alignment Requirements on COC Coating Reflectivity
• T010103, Advanced LIGO Suspension Conceptual Design Document
• T010007, Cavity Optics Suspension Subsystem Design Requirements Document
Definitions
See E010613, Generic Requirements and Standards for Detector Systems for a complete list of acronyms and names.
Physical Characteristics
All Advanced LIGO suspensions are designed to fit within the existing vacuum chambers, utilizing the Advanced LIGO SEI isolation systems The BSC chambers will accommodate the ITM, ETM, BSC, and FM suspensions, while the HAM chambers will house the remaining suspensions.
Interfaces External to LIGO Detector Subsystems
The assembly and installation processes must align with the specific constraints and sequencing of the LIGO site, ensuring compatibility with the site's emergency action plans, security protocols, and laser safety measures Adherence to these safety procedures is essential, as outlined in the Applicable Documents.
Interfaces to LIGO Detector Subsystems
The key document that records the interfaces between the detector subsystems is E030647 RODAs are used to record decisions and agreements between members of one subsystem and between subsystems The RODA Status Page may be found at http://www.ligo.caltech.edu/~coyne/AL/project_management/RODA/RODA_status.htm
The interface between the COC and SUS subsystems is designed to prioritize the protection and coverage of optics, except when the optical surfaces are required for ear bonding or alignment studies This arrangement is formalized in RODA M040091, which outlines the specific terms of the agreement.
The SUS subsystem aims to enhance the interface between AOS, IAS, and SUS by incorporating design and fabrication aids for alignment This includes fixed-distance crosshairs from the optic's centerline and mounting provisions for an alignment prism A signed RODA, M050174, outlines the specifics of this agreement.
Reliability
This section focuses exclusively on nominal operating conditions and does not cover accidents, such as personnel applying excessive current to an OSEM, or design failures in other subsystems, like insufficient AOS beam blockage that could lead to cutting of fiber or wire.
The failure rate for the ensemble of all in-vacuum components in all suspensions shall be at least 5 years per interferometer at the 99% probability level
The failure rate for the ensemble of all in-air components/equipment shall be at least 6 months at the 99% probability level.
Maintainability/Repairability
In-air components
The Mean Time To Repair (MTTR) in-air components shall be less than one day Spares for all in- air components will be kept at the sites.
In-vacuum components
The document "Advanced LIGO Quadruple Pendulum Suspension Failure Modes and Subsequent Repair Approaches, E040329" outlines various failure scenarios and repair strategies A forthcoming document will address repair methods for HAM cavity suspensions It evaluates whether repairs require complete removal of the suspension and seismic isolation (SEI) system or if only the bottom of the suspension can be extracted through the side chamber door To enhance efficiency, BSC suspension designs aim to minimize the need for cartridge de-installation, thereby reducing mean time to repair Additionally, suspensions in HAMs are designed for individual removal, avoiding the need to dismantle the entire seismic isolation system.
Repairs on fused silica suspension fibers and ribbons cannot be performed in-situ, as the welding process requires an external CO2 laser Consequently, any broken fibers or ribbons necessitate partial removal of the suspension The repair process should take no longer than two days, not accounting for the time needed to open the chamber, vent, pump down, or prepare the facility Additionally, this timeframe does not include the preparation for fabricating, characterizing, or selecting replacement fibers or ribbons The two-day period does encompass the cleanup of glass fragments and other debris resulting from the failure.
The duration of wire repairs is influenced by the wire's location and any associated damage To facilitate easier wire replacement, designs have been introduced that secure the optics and blades in place Repairs utilize a spare, pre-loaded, and pre-tested clamp-wire-clamp assembly, ensuring efficient wire installation The drum-ended wire design allows for timely repairs, with the entire process, including cleanup of glass fragments and debris, expected to be completed within two days, excluding additional preparations such as chamber opening, venting, and pumpdown.
In the event of ear damage to a test mass optic, it must be replaced with a spare Currently, we assume that test mass spares, whether in process or on the shelf, will not have bonded ears, while penultimate mass spares will Therefore, adequate time must be allocated for selecting a test mass spare, bonding and curing a new set of ears, and reinstalling the test mass optic This entire procedure should not exceed fifty days, with the actual replacement of the optic taking no more than two days, excluding the time required for chamber opening, venting, pumpdown, and facility preparation.
Sensor and actuator components must be easily replaceable within the suspension system without removing it from its location Repair times should be limited to a maximum of two days, not counting the time required for chamber opening, venting, pumpdown, and facility preparation.
Magnets used for force actuation with a coil are attached either by screwing them into metal masses or bonding them onto optical material masses It is expected that the ears and magnets will be bonded to identical spare penultimate masses The replacement of magnets due to optics should not take longer than 14 days, excluding the time for magnet assembly, optic preparation, chamber opening, venting, pumpdown, and facility setup Conversely, replacing a screwed-in magnet should not exceed 2 days, also excluding the necessary preparations and chamber activities Additionally, the process will involve locating and removing any broken magnet assembly components.
Any necessary mechanical adjustments, such as re-aligning eddy current dampers, sensors, and actuators in relation to magnets, must be completed within a maximum of two days, ideally aiming for just four hours This timeframe does not include the time required for chamber opening, venting, pumpdown, and facility preparation.
Environmental Conditions
Natural Environment
Fused silica fibers will be fabricated and stored in a controlled low-humidity, low-dust environment at the observatories Each suspension assembly will occur in an outbuilding using clean parts and metal masses, with the option for partial disassembly if needed After assembly, the suspensions will be wrapped in UHV foil, double bagged in C.P Stat, and stored in shipping containers indoors The welding of the fused silica fibers onto the suspension masses is expected to take place in a clean room near the appropriate chamber, with transportation of the suspensions limited to very short distances post-welding.
The temperature and humidity conditions for the various locations and major assembly and installation steps is indicated in Table 1 below.
Condition Temperature and Humidity Comments
Non-Operating: Storage of non-fused silica parts
10C to 38C, 0 to 90 % RH (non-condensing) storage indoors, but with minimal conditioning
Any special storage containers to maintain cleanliness are provided by SUS
Non-operating: storage of fused silica fibers in special containers
Container storage in environment typical of extremes for lab and office spaces
Low humidity containers for fiber/ribbon storage are provided by SUS
Non-operating: storage of COC/bonded-ear assemblies
RH 2 Containers for storage are provided by
Non-operating: accelerated creep bake maraging steel blades are loaded and held down in position with set screws (within
~+/1mm), and baked in air at
100 deg C for 110 hour to as an anti-creep measure
SUS sub-assemblies are baked The oven is provided by SUS.
Non-operating: low temperature, in-vacuum bake
46C, in-vacuum (