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Liquid Nitrogen Cooled SQUID Magnetometer for TEM

Andreas Chwala1, Ronny Stolz1, Marco Schulz1, Frank Previous HitBauerTop1, Rob Ijsselsteijn1, Eddie Köstlin2, and Hans-Georg Meyer1
1Quantendetektion, IPHT Jena e.V., Jena, Germany
2Private Consultant, Johannesburg, South Africa

SQUID magnetometers used in Transient Electromagnetics (TEM) surveys have become a valuable tool for exploring difficult targets during the last decade. Over the past 12 years, IPHT has developed SQUID systems for TEM applications, based on "High Temperature" Superconductors (HTS, Yttrium-Barium-Copper-Oxide YBCO), cooled with liquid nitrogen at 77 K. Test measurements on many targets of very different geological and climatic conditions demonstrated, that SQUID sensors are reliable and can outperform conventional induction coils, especially in late time applications. The latest version developed by IPHT uses ac-bias technology in order to overcome excessive low frequency noise and has recently been tested in Portugal. Excellent signal-to-noise-ratio at late time is shown in comparison to a Crone and Zonge coil; transients and profiles compare well to "LandTEM", a SQUID system developed by CSIRO in Australia.

IPHT SQUIDs, based on Low Temperature Superconductors (LTS, Niobium Nb), cooled by liquid helium down to 4K, have been used in production mode for several years now in South Africa and Australia by Anglo American.

Gradiometers SQUIDs are able to measure the magnetic gradient directly with a very high resolution of better than 1pT/m in a 10Hz bandwidth. A short introduction of the new instrument "Jessy Star" will also be given.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery