Participants:

C-1:Cryogenic last-stage suspensions (interferometers) (F.Ricci-G.Frossati)Objectives: -Design new suspension elements for the last stage of interferometers.-Achieve a low noise remote control of the mirror position using cryogenic sensors-Assemble and test of a full-scale prototype of cryogenic final stage C-2:Cryogenics suspensions for advanced interferometers (G.Frossati-M.Bassan)-Objectives:-Two 1.2 ton spheres with their suspension assembled and measurementsof Q and thermal noise at low temperature performed.C-3: Cryogenics suspension system for interferometers (S.Braccini-M.Bassan)Objectives:-The entire apparatus be located in a cryogenic environment; the extra noise coming from the cryogenic system be studied and made negligible.-Full cryogenic suspension be assembled and tested

Participants:Participants: INFN ROG

Leiden University

Tasks: - Cool down of Minigrail to 50 mK- Investigation of heat transfer from the mixing chamber to the sphere

Deliverables: - Report on mechanical transfer function

measurements of cryogenic suspension

Cryogenic suspension system for advanced resonant detectors

MiniGRAILCryogenics

cryostat

Liquid N2 77K (-196 ºC)

Liquid He4K (-269 ºC)

Dilution refrigerator(10 mK)

MiniGRAILCryogenics; The dilution refrigerator

still(700 mK)

50 mKplate

mixingchamber(10 mK)

To 50 mK shield

To mixing chamber

CryogenicsThermal anchoring suspension

To still shield

CryogenicsRun 4

Minimum temperatures:Tsphere = 80 mKTmc = 20 mK

Time dependent heat leak from sphere:

45 W after 6 weeks

Vibration Isolation System

1

2

3

4

5

6

7Attenuation cables

+ absorbers

Vibration Isolation System

1

2

3

4

5

6

7

Attenuation between mass 1 and 2

• Larger diameter (68 cm instead of 65 cm) gives lower frequency and higher mass (1300 kg instead of 1150 kg).

• Six holes machined in TIGA positions

The new sphere

Resonance frequencies of bare sphere at 300 K

Old sphereNew sphere

Frequency of new sphere about 200 Hz lower

Improvements on the Vibration Isolation System

370

370

370

370

370

370

370

Material before (mm) fbefore (Hz)

CuAl 1,2 370 3516

CuAl 3,4 370 3516

Cu 5-7 370 3397

Improvements on the Vibration Isolation System

370

370

362

362

358

358

358

Material before (mm) fbefore (Hz) after (mm) fafter (Hz)

CuAl 1,2 370 3516 370 3516

CuAl 3,4 370 3516 362 3633

Cu 5-7 370 3397 358 3512

Improvements on the Vibration Isolation System

370

370

362

362

358

358

358

~ 50 dB

Closed Membrane Capacitive Transducer

Advantages:• Compact design• Easy to make

electrode

membrane

mass (~ 200 g)

spring

CuAl6%

d ~ 30 micro mVBIAS up to 500 V

Cryogenic run

transformer +2-stage SQUID

calibrator

3 hour acquisition @ 5K of mode 3 (2943 Hz)

exponential fit

Teff = 70 mK

MiniGRAIL sensitivity - run 6

1.5 x 10-20

MiniGRAIL sensitivity - run 6

Run 6

T 5 K

700 ħ

Q 105

M 200 g

C 1.1 nF

Vbias 200 V

Run 7

T 80 mK

100 ħ

Q 106

M 400 g

C 1.5 nF

Vbias 400 V

Teff = 40 K4 x 10-22

MiniGRAIL sensitivity - comparison

Initial target large interferometers

LIGO S3

GEO

AURIGA

NAUTILUS/EXPLORER

MiniGRAILrun 6

Planned at the end of 2004

MiniGRAILrun 7