1

New suspension study for LCGT

Erina NishidaOchanomizu UniversityThe Graduate School of Humanities and Sciences The Division of Advanced Sciences/ NAOJ

LCGT f2f meeting@Tokyo university, Japan, 5th Aug, 2011 Erina Nishida 2

LCGT Sensitivity There is a peak at 117Hz

Those depends on the fiber being thick and tunnel tilting.

bLCGT default parameters Arm length: 3000[m] Test mass: 30[kg] Mass temperature: 20[K] Suspension length: 0.3[m]

LCGT f2f meeting@Tokyo university, Japan, 5th Aug, 2011 Erina Nishida 3

troublesome peak from data analysis

•One of problem for data analysis is vertical mode at 117Hz

•LIGO mode frequency is about 300～ 400Hz.•Sensitivity is worse.( lower S/N→lower detection efficiency)•Power is unstable.(power fluctuation make detection efficiency worse)

•It is difficult to analyze this frequency band.

•Frequency band this mode could be widen. >> Laser amplitude noise, seismic noise, 4 wires…

LCGT f2f meeting@Tokyo university, Japan, 5th Aug, 2011 Erina Nishida 4

Simulation model

wh

Mathmatica Model parameters ●4 sapphire suspensions●0.30 m length● 30kg mass

r

fiber ribbon

LCGT f2f meeting@Tokyo university, Japan, 5th Aug, 2011 Erina Nishida 5

Why fiber is not effective??

angle loss

widthribbon thickness ribbon fiber,

ribbon fiber, suspension of number

(ribbons)

(fibers)

:,

::,

:,

2

3

2

4

12

4

rf

wrdfdrNfN

rr

ff

MgL

whYN

MgL

dYN

length filament the

onaccelerati nalgravitatio

mass supported the

inertia of moment sectional-cross

modulus s Young'

:

:

:

:

:

22

1

L

g

M

I

Y

MgL

YI

Physics Letters A 270 (2000) 108-114

‘Ribbon’ thickness could be thinner while the heat transportation keep.

wireof numberN;

tyconductivi thermal

effect cooling

;

dTNl

AW

Mechanical lossΦ

LCGT f2f meeting@Tokyo university, Japan, 5th Aug, 2011 Erina Nishida 6

Moving 120Hz peak by changing the fiber shape

mass wirem;

mode violin

m

M

l

gn

●

•Including cooling effect, those peaks doesn’t move to lower.•Without thermal noise increasing, how to make the peak decrease….isRibbon, which could make cross section larger, then resonant frequency higher.

suspension of section cross A;

length suspension l; module, youngY;

mode vertical

4/

/*

mass

lYAv

●

LCGT f2f meeting@Tokyo university, Japan, 5th Aug, 2011 Erina Nishida 7

Ribbon cross section constantRibbon thickness h,　 width wCooling effect　 above 0.8W

Comparison of different ribbon ratio

Thin ribbon can make violin mode move to higher.

Thinner ribbon make 2nd mode To 500Hz!!

LCGT f2f meeting@Tokyo university, Japan, 5th Aug, 2011 Erina Nishida 8

Ribbon width constantRibbon thickness hCooling effect　 above 0.8W

Comparison of different cross sections

Vertical mode and violin mode move to higher according to the thickness.

7times area make 1st mode to 300HzThose parameters are realistic!!

LCGT f2f meeting@Tokyo university, Japan, 5th Aug, 2011 Erina Nishida 9

VSPI for vertical mode Vertical mode could be suppressed by VSPI.

•Resonant frequency can be changed.

•Thermal noise can be reduced.

Feedback control

[Vertical Suspension Point Interferometer]

Alternative solution to reduce vertical TN

LCGT f2f meeting@Tokyo university, Japan, 5th Aug, 2011 Erina Nishida 10

Options for solutions

To avoid the suspension peak at the117Hz

→Use ribbon which has

wide width and thin thickness

To avoid vertical mode

→vertical SPI

Thank you for your attentions!!