TAMA300の現状(15) - JGW Document Server

Vibration Isolation Group
Two-layer configuration
(1) Budget → tunnel group
(2) Schedule
(3) Installation and Maintenance
(4) Short Inverted Pendulum
LCGT
A-review of VIS
(20 Dec., 2010)
Generalities

4m φ (→8m x 12m) x 4m h
(→7m) upper tunnel containing
pre-attenuator

1.2m diameter 5m tall borehole 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 3.42mm
x 2.1m x 0.8m
Filter1
3.44mm 3.42mm
x 2.1m x 0.8m
Filter2
3.11mm 3.98mm
x 2.1m x 7.0m
Filter3
2.74mm
x 2.1m
CB
2.45mm 2.44mm
x 1.0m 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 preisolator tuning
Performance of IP
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.

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