1 New suspension study for LCGT Erina Nishida Ochanomizu University The Graduate School of Humanities and Sciences The Division of Advanced Sciences/ NAOJ

LCGT f2f 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 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 university, Japan, 5th Aug, 2011 Erina Nishida 4 Simulation model Mathmatica Model parameters ●4 sapphire suspensions ●0.30 m length ● 30kg mass fiberribbon

LCGT f2f university, Japan, 5th Aug, 2011 Erina Nishida 5 Why fiber is not effective?? Physics Letters A 270 (2000) ‘Ribbon’ thickness could be thinner while the heat transportation keep. Mechanical lossΦ

LCGT f2f university, Japan, 5th Aug, 2011 Erina Nishida 6 Moving 120Hz peak by changing the fiber shape Including cooling effect, those peaks doesn’t move to lower. Without thermal noise increasing, how to make the peak decrease….is Ribbon, which could make cross section larger, then resonant frequency higher.

LCGT f2f university, Japan, 5th Aug, 2011 Erina Nishida 7 Ribbon cross section constant Ribbon thickness h, width w Cooling effect above 0.8W Comparison of different ribbon ratio Thin ribbon can make violin mode move to higher. Thinner ribbon make 2 nd mode To 500Hz!!

LCGT f2f university, Japan, 5th Aug, 2011 Erina Nishida 8 Ribbon width constant Ribbon thickness h Cooling effect above 0.8W Comparison of different cross sections Vertical mode and violin mode move to higher according to the thickness. 7times area make 1 st mode to 300Hz Those parameters are realistic!!

LCGT f2f 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 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!!