G M Advanced R&D1 Seismic Isolation Retrofit Plan for the LIGO Livingston Observatory Dennis Coyne 29 Nov 2001

G M Advanced R&D2 Issues Spiky seismic noise Hz band »related to human activity, especially cutting lumber »worst at y end, appears as wide band noise through narrow band filter »coincident with transmission peak in test mass isolation stack and seismic amplification in the soil under the Y-end station »precludes interferometer lock during work day »Rayleigh surface waves: vertical/ horizontal = 1.5/ 1, meters/ sec Most likely growing with epoch, tracking population »1988 LSU survey: not evident »1995 Rohay study: about 1/ 2 as large and 1/ 2 rate of today »need to include margin in fix Strategy to deal with the noise »higher peak current controller: short term, adds noise »active external isolation: short study, feedback, feed forward……. »need to be installed before reaching design sensitivity - 1 year

G M Advanced R&D3 Improved Seismic Isolation Improved isolation is essential for Test Masses – BSC Chambers »Need factor of ~20 reduction in the rms motion between 1 and ~5 Hz (Firm requirements are being developed) Improved isolation for the Mode Cleaner optics may be necessary – HAM chambers »Simulation is being developed to study the effect of the resulting frequency noise & modest means of reducing the rms

G M Advanced R&D4 Improved Seismic Isolation Industry »No current commercial off-the-shelf system is directly applicable »Have contacted some isolation specialty firms – not promising »Reluctant to place the responsibility out-of-house as the problem is clearly unique & challenging for industry »Will continue to study adaptation of TMC’s STACIS system; others possibly Fine Actuators »Existing single degree of freedom actuation system (piezoelectric) used for tidal correction and microseismic feedforward compensation could be employed for isolation (feedback or feedforward) »Considerable cross-coupling in the stack modes makes this approach unlikely to succeed »Experiments at Livingston are planned

G M Advanced R&D5 Improved Seismic Isolation Tuned Mass Damping »Passive method to increase modal damping; requires (perhaps brief) entry into the vacuum system »Unlikely to get more than a reduction of a factor of ~8 »May suffice for the HAM stacks, or may help an active system on the BSC »Analysis is underway Active 6-dof pre-isolator »Preferred approach »retrofit fine/coarse actuation with an active pre-isolation system under the existing passive isolation stacks; hope to preserve alignment »Leading candidate is the hydraulic actuator that the LSC (Stanford) is developing for advanced LIGO »Alternate actuators (e.g. piezo, EM) are under study in parallel

G M Advanced R&D6 Hydraulic system

G M Advanced R&D7 Hydraulic prototype test results 2-DOF system Feedforward and feedback Potential to reduce ambient seismic noise also for initial LIGO if indicated

G M Advanced R&D8 Implementation Actuator prototypes & component test stands are underway at Stanford for the actuator and sensors; at MIT for the hydraulic distribution system Full scale prototype system test including retrofit installation is planned on the LASTI BSC »BSC stack has been installed Long lead items procured in parallel with prototype testing Team »Accelerated development by the existing LSC adv. LIGO team, augmented by LIGO Lab staff »Effort transitions out of LSC R&D & into Lab implementation through the LASTI prototype development

G M Advanced R&D9 Schedule & Cost Preliminary Design Review in Jan »System modeling results »Sensors selected & characterized »Hydraulic actuator prototype tested (bolted version) »Distribution system designed & modeled Prototype installation & LASTI: May – Sep Installation at Livingston starts Oct Rough estimate is ~$750K »for 4 BSCs, 2 HAMs »beyond the R&D costs associated with the prototype development (which is mostly part of the existing R&D plan)