September 23, 2004Univeristy of Twente1 Superconducting Gravity Gradiometry State of the Art

September 23, 2004Univeristy of Twente2 Superconducting Gravity Gradiometry  Present status  Key technologies  Conclusions

September 23, 2004Univeristy of Twente3 Present status: low-Tc

September 23, 2004Univeristy of Twente4 Maryland design (Paik et.al. 1996/2002)  Noise level: 20 mE /Hz (4 mE /Hz)  CMRR (lin.): 10 4

September 23, 2004Univeristy of Twente5 Oxford Instruments (2001)  CMRR: 810 4 (>10 6 )  Noise level: 180 mE/Hz (?) (1 mE/Hz)

September 23, 2004Univeristy of Twente6 UWA (van Kann et.al. 2002)  Noise level: 0.5 E/Hz  CMRR (ang.): >10 4 (10 6 )  CMRR (lin.): 10 9 (310 10 )

September 23, 2004Univeristy of Twente7 Gravitec (Veryaskin 2000)  Noise level: 3 E/Hz  CMRR: ?

September 23, 2004Univeristy of Twente8 Univ. Kharkov (verozub 1996) F = 0 for I 1 = 0.  Magnetic levitation of proof mass  Low intrinsic noise level…  Lateral stability…  Potential for miniaturization…

September 23, 2004Univeristy of Twente9 High-Tc  High-Tc conceptual design study on basis of Maryland device 1  Predicted sensitivity 4 mE/ 1 Hz and 77 K 2.5 mE/ 0.1 Hz and 28 K 1 C.S. Jacobsen et. al., Conceptual Design of a Gravity Gradient sensor based on high Tc superconducting technology, ESA contract 9031/90/NL/PB CCN2 final report May 1995

September 23, 2004Univeristy of Twente10 Key technologies: materials  Low-Tc 4 K  High-Tc 77 K Bi, Tl, Hg families  MgB 2 Tc of 39 K, operating temp. 35 K  Test masses High quality Nb or Si

September 23, 2004Univeristy of Twente11 Key technologies: SQUIDS  Low-Tc Nb: improved sensitivity Well developed technology  High-Tc YBCO: limited progress since 1995 Lifetime: no significant improvement Coupling coils: still difficult (T)  MgB 2 Research in full swing At present no sophisticated junction technology More work needed

September 23, 2004Univeristy of Twente12 Key technologies: levitation coils  Nb Fulfils requirements  BSCCO Joining still a problem Tapes 0.2x5 mm 2 (big) Geometry: react after wind, limited strain Other materials not suitable  MgB 2 First results wit powder in tube, but improvement in properties needed Joints not yet realised

September 23, 2004Univeristy of Twente13 Key technologies: electronics  SQUID electronics for both low-Tc and high-Tc has improved in sensitivity and speed  Modulation techniques are available for improved signal to noise ratios at low frequencies

September 23, 2004Univeristy of Twente14 Key technologies: cooling 1  Cooler mass 4K  100 kg 35K  10 kg 77K  1 kg Recent overview for cryocoolers in space: ISEC, 6-9 september 2005, Noordwijkerhout

September 23, 2004Univeristy of Twente15 Key technologies: cooling  Efficiency: P 0.3W 4K 40K 77K

September 23, 2004Univeristy of Twente16 Key technologies: cooling  Mass vs. volume

September 23, 2004Univeristy of Twente17 Conclusions  Low-Tc: possible, size reduction possible, cooler has large mass and requires a lot of power  MgB 2 : research is underway, has to prove itself, cooling hast intermediate mass and power requirements  High-Tc: looks possible when several practical issues have been solved (maybe hybrid structure with MEMS), cooler has acceptable mass and power requirement

September 23, 2004Univeristy of Twente18 High-Tc  Mechanical No specific improvements (Q)  Thermal Cooling technology improving, but reliability and lifetime insufficient

September 23, 2004Univeristy of Twente19 Noise in small Gradiometer:  Thermal gradiometer noise  M=0.1kg; T=4K; Q=10 5 ; f 0 =1Hz; b=0.1m; Miniaturization

September 23, 2004Univeristy of Twente20 M=1 kg, b=1 m, Q=10 5 M=1 kg, b=0.1 m, Q=10 5 M=1 g, b=0.1 m, Q=10 5 M=1 g, b=0.01 m, Q=10 5 Miniaturization

September 23, 2004Univeristy of Twente21 Miniaturization  High-T c Coils, squids and cooling make a superconducting High-Tc SGGM not feasible  Low T c Maryland/Oxford approach… Kharkov approach…

September 23, 2004Univeristy of Twente22  Reduced mass smaller dimensions everything closer together   Coils geometry problems increase  stray couplings increase   Mechanical alignment etc. more difficult  Miniaturization Maryland/Oxford approach

September 23, 2004Univeristy of Twente23 Miniaturization Maryland/Oxford approach  Thermal Liq.-He bath not suitable for planetary mission: long lived 4K mechanical cooler?   Technical Problems are already conside- rable without miniaturization  The technical challenge of realizing a low-Tc Maryland/Oxford-type SGG is considerable. Miniaturization will be difficult and a reliable ‘low mass’ 4K cooler is not yet available.

September 23, 2004Univeristy of Twente24 L1I1L1I1 L2I2L2I2 M Miniaturization Kharkov approach  Reduced mass smaller dimensions  Coils 2-D coil arrangement possible that can easily be scaled down  Mechanical Magnetic spring determined by electrical currents alignment of measurement axis 

September 23, 2004Univeristy of Twente25 L1I1L1I1 L2I2L2I2 M Miniaturization Kharkov approach  Thermal Liq.-He bath not suitable for planetary mission: long lived 4K mechanical cooler? Realization of a miniature Kharkov-type SGG seems feasible in low-Tc. A reliable ‘low mass’ 4K cooler is not yet available