1. 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

2. 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

3. (2) Schedule

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

5. 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.

6. 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

7. (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

8. 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

9. 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

10. 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.