1. Some ideas on advanced Virgo Twins A. Giazotto-INFN Pisa
If this is true, one appealing idea could be to build a second Virgo:

2. Some interesting test on twin beams
1)Direct measurement of Scattered Light Effect on the Sensitivity in TAMA300
Ryutaro Takahashi, Koji Arai, Seiji Kawamura and
Michael Smith*
National Astronomical Observatory of Japan, Caltech*

3. Experimental method
Vibrate the mid point of the arm using a shaker vertically.
5.6 x
4.7 x
Measure the effects due to vibration and sound.

4. Experimental result 1 (signals of the interferometer)

5. Results and discussion
776.5Hz Hz
Interferometer 1.2 x 10-17m x 10-17m
(Background) x 10-17m x 10-17m
Vibration　 <0.1 x 10-17m <0.01 x 10-17m
Sound not detected x 10-17m
Calculation (with 2-m reflection area and optimal phase)
6.3 x 10-17m
There is cancellation due to mechanical modes.

6. Approximate Conclusions from TAMA TAMA Tube: Diam.~40 cm, No Baffles
Vibration 765 Hz :
~10-17/5 10-6=
Scale to Virgo Seismic noise in Virgo is expected to be xVirgo~10-7/2 m/Hz1/2
Expected seismic correlated signal in the two beams~ /2= /2 m/Hz1/2
Expected reduction due to Baffles~1/10 ~ /2 m/Hz1/2

7. 2)Preliminary data from 2km and 4km Hanford ITF’s seems to show low correlation.

8. From LIGO it seems that:
Seismic noise correlate up 30 Hz due to suspensions.
Switching power supply create bad correlations at 60 Hz harmonics; needed analog power supply and very good groundings.
3) Sound correlate on injection systems due to common housing.

9. Virgo seems to have an optimal configuration from three relevant points of views:
1) Very good seismic isolation down to 4Hz
2) Buildings for the second ITF may be completely separated from Virgo 1, this reduces a lot sound and e.m. couplings on the two injection systems.
3) Baffles are installed in the vacuum tube
4) We may also design the overall electronics to be powered with analog Power Supply.
5) A problem: overlapped beams may give coincidences due to dust falling in the vacuum pipe.

11. VIRGO 2
VIRGO1