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| Titel |
Prototyping a new, high-temperature SQUID magnetometer system |
| VerfasserIn |
J. Michael Grappone, John Shaw, Andrew J. Biggin |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250153710
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| Publikation (Nr.) |
 EGU/EGU2017-18723.pdf |
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| Zusammenfassung |
| High-sensitivity Superconducting Quantum Inference Devices (SQUIDs) and μ-metal
shielding have largely solved paleomagnetic noise problems. Combing the two allows
successful measurements of previously unusable samples, generally sediments with very
weak (<10 pAm2) magnetizations. The improved sensitivity increases the fidelity
of magnetic field variation surveys, but surveys continue to be somewhat slow.
SQUIDs have historically been expensive to buy and operate, but technological
advances now allow them to operate at liquid nitrogen temperatures (77 K), drastically
reducing their costs. Step-wise thermal paleomagnetics studies cause large lag times
during later steps as a result of heating from and cooling to room temperature for
measurements. If the cooling step is removed entirely, however, the lag time drops by at
least half. Available magnetometers currently provide either SQUID-level (0.1 -
1 pAm2) sensitivity or continuous heating. Combining a SQUID magnetometer
with a high temperature oven is the logical next step to uncover the mysteries of
the paleofield. However, the few that currently offer high temperature capabilities
with noise levels approaching 10 pAm2 require either spinning or vibrating the
sample, necessitating additional handling and potentially causing damage to the
sample.
Two primary factors have plagued previous developments: noise levels and
temperature gradients. Our entire system is shielded from the environment using 4 layers
of μ-metal. Our sample oven (designed for 7 mm diameter samples) sits inside a
copper pipe and operates at high-frequency AC voltages. High frequency (10 kHz)
AC current reduces the skin depth of radio frequency (RF) electromagnetic noise,
which allows the 2 mm-thick copper shielding to reduce RF noise by ∼94%, leaving
a residual field of ∼1.5 nT at the SQUID’s location, 14.9 mm from the oven. A
computer-controlled Eurotherm 3216 thermal controller regulates the temperature
within ± 0.5 ˚ C. To reach 700 ˚ C, just above the Curie temperature of Hematite, a
temperature difference of nearly 900 ˚ C between the sample and the SQUID is
required. Since dipole fields decay rapidly with distance (∝ r −3 ), the equipment
is designed to handle temperature gradients above 500 ˚ C cm−1 for maximum
sensitivity using a passive double-vacuum separation system. All the parts used are
commercially available to help reduce the operating costs and increase versatility. |
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