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 measurements of 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

MiniGRAIL Cryogenics cryostat Liquid N 2 77K (-196 ºC) Liquid He 4K (-269 ºC) Dilution refrigerator (10 mK)

MiniGRAIL Cryogenics; The dilution refrigerator still (700 mK) 50 mK plate mixing chamber (10 mK)

To 50 mK shield To mixing chamber Cryogenics Thermal anchoring suspension To still shield

Cryogenics Run 4 Minimum temperatures: T sphere = 80 mK T mc = 20 mK Time dependent heat leak from sphere: 45  W after 6 weeks

Vibration Isolation System Attenuation cables + absorbers

Vibration Isolation System 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 sphere New sphere Frequency of new sphere about 200 Hz lower

Improvements on the Vibration Isolation System 370 Material  before (mm) f before (Hz) CuAl 1, CuAl 3, Cu

Improvements on the Vibration Isolation System Material  before (mm) f before (Hz)  after (mm) f after (Hz) CuAl 1, CuAl 3, Cu

Improvements on the Vibration Isolation System ~ 50 dB

Closed Membrane Capacitive Transducer Advantages: Compact design Easy to make electrode membrane mass (~ 200 g) spring CuAl6% d ~ 30 micro m V BIAS up to 500 V

Cryogenic run transformer + 2-stage SQUID calibrator

3 hour 5K of mode 3 (2943 Hz) exponential fit T eff = 70 mK

MiniGRAIL sensitivity - run x

MiniGRAIL sensitivity - run 6 Run 6 T5 K  700 ħ Q10 5 M200 g C1.1 nF V bias 200 V Run 7 T80 mK  100 ħ Q10 6 M400 g C1.5 nF V bias 400 V T eff = 40  K 4 x

MiniGRAIL sensitivity - comparison Initial target large interferometers LIGO S3 GEO AURIGA NAUTILUS/EXPLORER MiniGRAIL run 6 Planned at the end of 2004 MiniGRAIL run 7