Vibration Isolation Group Two-layer configuration Budget → tunnel group Schedule Installation and Maintenance Short Inverted Pendulum LCGT A-review of VIS (20 Dec., 2010) 1

Generalities 4m φ (→8m x 12m) x 4m h (→7m) upper tunnel containing pre-attenuator 1.2m diameter 5m tall bore-hole with SAS chain 5.5m (→8m) tall containing main beam and cryostat

(2) Schedule

(3) Installation and Maintenance Ease of installation No need of large, expensive rigid structures Much lighter crane (1t) requirements

Disposition of GAS filters Case (1): 4 filers are placed every 2m. Eddy current damping to the Filter1 works effectively (<10min). Careful wiring between filters is necessary. One long wire (in TAMA) → Short wire chain with anchored connector. Case (2): 3 filters are inside the upper chamber. It is difficult to damp the torsion mode (>1h). If thick 7-m wire is used, a frequency of the wire resonance becomes too low (~10Hz). Maintenance of filters is easer.

Damping of torsion mode Case (1) Case (2) Filter0 3.74mm x 2.1m 3.42mm x 0.8m Filter1 3.44mm x 2.1m Filter2 3.11mm x 2.1m 3.98mm x 7.0m Filter3 2.74mm x 2.1m CB 2.45mm x 1.0m 2.44mm x 1.0m by T. Sekiguchi

(4) Short Inverted Pendulum Pre-isolator footed on solid rock It was found that small size = better performance Easy of access for pre-isolator tuning

Performance of IP Short IP is sensitive to the load. Performance by H. Ishizaki Short IP is sensitive to the load. Performance Long IP (NIM A582, 683) ~50dB Short IP (NIM A598, 737) ~80dB

Disadvantages Need new bore-holes to re-position any optical element Need to know where to locate all mirrors ! Will need 1200 mm diameter or oval boreholes to allow for ±100 mm tuning of PR, SR, ITM mirrors

In the case of one layer. External rigid structure Base for IP on bottom of the chamber like TAMA-SAS → It is difficult to apply to Type-A system.