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Perspectives about the capacitive-SQUID readout for the next run of AURIGA

Perspectives about the capacitive-SQUID readout for the next run of AURIGA. Andrea Vinante (University of Trento and INFN Padova) e-mail: vinante@science.unitn.it. S hh : 1st run (97-99) and 2th run (04-06…). (FWHM) bandwidth enlarged : Dn= 26 Hz (1st run Dn 1 Hz ).

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Perspectives about the capacitive-SQUID readout for the next run of AURIGA

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  1. Perspectives about the capacitive-SQUID readout for the next run of AURIGA Andrea Vinante (University of Trento and INFN Padova) e-mail: vinante@science.unitn.it A. Vinante

  2. Shh: 1st run (97-99) and2th run (04-06…) • (FWHM) bandwidth enlarged: Dn=26 Hz (1st run Dn1 Hz) Shh<10-20 Hz-1/2 over110 Hz (25 Hz) • Teff=320 mK at T=4.5K (2th run Teff>1mK at T=0.1K) (L. Baggio et al, Phys Rev. Lett. (2005) ) A. Vinante

  3. Implementation of a two-stage SQUID amplifier • Reduced amplifier noise Main new features • First operation of a resonant capacitive transducer with 2 effective modes (mechanical + electrical) tuned to the bar mode for a 3-modes operation • Increased coupling between bar and amplifier A. Vinante

  4. Bar Matching transformer Two-stage SQUID Intrinsic Q line Shielded resonant transducer Bias field line Feedback electronics Calibration line The AURIGA readout: scheme A. Vinante

  5. The AURIGA readout: compact assembling Shield plate High voltage plate Resonant transducer Mounted on the face of the bar Decoupling spring Cryogenic switch Decoupling capacitor box Superconducting transformer and SQUID box A. Vinante

  6. The shielded “heavy” transducer HV plate Main resonator Teflon spacer Effective resonator mass (from Dn): 6.1 kg Mechanical resonance frequency: 898.4 Hz gap=40 mm, capacitance=8.5 nF A. Vinante

  7. AURIGA output spectrum Typical spectrum averaged on 8 consecutive hours Main modes = mixing of bar, transducer and electrical modes: 865, 914, 955 Hz A. Vinante

  8. Mechanical transfer function 3-modes fit • Experimental transfer function. Force applied by a capacitive force actuator. • Spurious modes not considered. Work in progress to include them in model A. Vinante

  9. AURIGA Shh: Noise budget • Theoretical prediction by three-modes numerical model (spurious modes not included!). • Most parameters of the model directly measured “in situ”. • Transfer functions: • Mechanical: 1 Zero (Bar mode) • Electrical+BA: 2 Zeroes (2 mechanical modes at zero field) • Additive: 3 Zeroes (3 modes) A. Vinante

  10. Mechanical thermal noise T=4.5 K Qmec=1.5-4 106 Referred to a force on the bar: • In principle there is large reserve for increasing Qmec. Intrinsic Q of material (Al5056) is at least 1 order of magnitude higher (Ex. 2 spurious modes at 2.1 kHz exist, with Q=8107 !). Probably Q is degraded by clamping screws. Important issue to solve for next generation detectors. • Simpler way to reduce thermal noise is cooling to ultracryogenic temperature. Target temperature is 100 mK (roughly obtained in AURIGA first run and NAUTILUS. Even lower in MINIGRAIL). • Ultracryogenic run scheduled for beginning 2007 (Not possible now because some modifications are needed to insert the dilution refrigerator) A. Vinante

  11. Electrical mode: the high Q transformer • Primary coil: Lp=7.9 H • Secondary coil: Ls=3.2 mH • High coupling factor k=0.86 • Reduced stray capacitanceCp=10 pF(coil by sections) • Effective inductance (reduced by coupling to SQUID input): • Leff=3.8 H • Electrical mode (transformer effective inductance + transducer capacitance) • Resonance frequency nel=941 Hz • Quality factor Qel=1.3x106 when not coupled to SQUID • (Qel=4.7x105 when coupled to SQUID) SQUID insertion adds dissipation! A. Vinante

  12. Electrical thermal noise Qel=4.7105 E=7.5 106 V/m • Within present experimental setup, referred to the bar: • Two components of Qel: intrinsic electrical (dielectric and magnetic dissipation in transducer + superconducting transformer) and from SQUID input circuit (equivalent to back-action). Qint  1.3106 QSQ  7.4105 Seems difficult to increase significantly Qint . Recently tested a SQUID with QSQ factor >10 higher. Not yet demonstrated stability and reliability when coupled to a high Q resonant load. • Seems much more effective to increase bias field E A. Vinante

  13. Effect of increasing bias field Maximum realistic target for AURIGA ultracryogenic run: E x 2.5 (DUAL R&D target: factor >10 , Factor 6.5 already obtained on small samples) 1) Mechanical unchanged 2) Electrical + BA decreases (as 1/E) A. Vinante

  14. Electrical thermal noise at ultracryogenic T • Problem: poor thermalization (very low thermal conductivity of superconductors and polymers) at 100 mK. • High Q LC resonator cooled by means of a dilution refrigerator. Inductance (NbTi coil in SnPb shield) and capacitance (Teflon capacitors) elements with similar technology with respect to AURIGA ones. • 3He or 4He exchange gas. LC thermal noise scales down to 60 mK ! (A. Vinante et al, Rev. Sci. Instrum. 2005) A. Vinante

  15. SQUID noise Two components: • Back-action (Svv) • Additive (SII) True energy sensitivity. (TN noise temperature) Main achievements of recent years: 1) Two-stage configuration Noise is close to the thermal limit in both components (TN  T), down to T200 mK 2) Damping network for stabilization of SQUID + high Q resonant loads Noise can be optimized when the SQUID is operated on the real detector A. Vinante

  16. AURIGA-SQUID at ultracryogenic T • AURIGA-like SQUID (two-stage Quantum Design) coupled to a high Q LC resonator (11 kHz) • e scales with T down to 200 mK as predicted. Best value 27 h. History of improvements of Trento SQUID noise in recent years A. Vinante

  17. AURIGA ultracryogenic: design sensitivity Ultracryogenic operation (like AURIGA first run): T=100 mK All noise components in AURIGA decrease WITH T! • SQUID noise saturation at 200 mK taken into account. • Mechanical and electrical noise assumed thermal (scale with T down to 100 mK). • Quality factors assumed constant. A. Vinante

  18. Emin 110 hw kBTN  55 hw Ultracryo run prediction (T=0.1 K, E x 2.5) How far from quantum limit? Minimum detectable energy SQUID noise energy Emin 7000 hw kBTN  550 hw Present run experimental (T=4.5 K) Emin 62 hw kBTN  12 hw Ultracryo with a better SQUID * Note: SQUID noise includes excess dissipation from input circuit and non-thermal 1/f noise contribution * Manufactured by IBM. kBTNestimated from bench tests (additive noise and excess dissipation), but not yet demonstrated operation on a high Q resonator and reliability. Ultracryo case much closer to the matching limit (factor 2). Crucial factor is the increase of bias field E A. Vinante

  19. Current R&D on SQUIDs • Better SQUIDs. In the near future plan to operate a SQUID with kBTN 10 hw coupled to a high Q resonator. • Reduce (non-thermal) 1/f noise (Recent indications point to weak magnetic impurities near the SQUID loop). • Reduce excess dissipation in the input circuit (i.e. increase electrical Q factor) • Improve thermalization of shunt resistors, in order to avoid the saturation of electron temperature at 200 mK. Can be achieved by using cooling fins. Collaborations: • Giessen University • Twente University (MINIGRAIL) A. Vinante

  20. R&D on voltage breakdown (DUAL R&D) M. Bonaldi, F. Penasa IFN Trento Apparatus for High voltage study Measurement of V.B. of Al5056 polished surfaces of cylindrical samples Goal: 108 V/m Achieved: 50 MV/m A. Vinante

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