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news release:
ORNL uses nanodots
to boost superconductivity
Oak Ridge, TN, Apr. 3:
Oak Ridge National Laboratory
researchers have demonstrated a way to sustain high supercurrents in wires in
the presence of a large applied magnetic field -- a step which could greatly
expand practical applications of superconductors.
By creating columns of self-aligned,
non-superconductive "nanodots" within the superconductor, the ORNL team has
produced a high-temperature superconductor that works even in a powerful
magnetic field.
The ORNL work, reported in the current issue of
Science, increases the plausibility of high-temperature superconductors in
motors, generators, air defense systems and other applications once limited by
the negative effects of applied magnetic fields.
Lead author for the Science paper is Sukill Kang,
a post-doctoral fellow in the Materials Sciences and Technology Division at ORNL.
Kang's mentor, Amit Goyal, is an ORNL
distinguished scientist and the project's technical leader who also co-developed
the rolling-assisted-biaxially-textured substrates (RABiTS) process which
deposits brittle, ceramic-like high temperature superconducting materials onto a
substrate, or template, that gives the wires the texture, flexibility and
mechanical strength of metal.
Superconductors carry large amounts of current
when cooled, offering much more efficient energy transmission for a wide range
of uses. Advances in achieving supercurrent at higher temperatures with liquid
nitrogen, which is more practical than liquid helium needed to cool older
superconductors at lower temperatures, have made the technology more applicable.
However, magnetic fields have remained an
obstacle to many superconductor applications, Goyal said. The problem is that
naturally occurring vortices -- whirling cylindrical forces between the atoms of
the superconducting material -- begin to move about under applied magnetic
fields, creating electrical resistance and power dissipation. Large scale
supercurrents can flow only if these vortices remain firmly locked in place, or
"pinned."
ORNL's answer was to incorporate "misfit"
nanodots of non-conductive material throughout the entire thickness of the
superconductor and effectively pin the vortices and prevent their movement,
enabling high supercurrents even in the presence of high applied magnetic
fields.
"Most applications of superconductors require the
superconductor to be in large applied magnetic fields," Goyal said. "Thus, to
truly sustain very high current in strong magnetic fields, you must prevent the
vortices from moving.
"One way to do that is to have
non-superconducting regions which "pin" or prevent these vortices from moving.
They provide a barrier. To get adequate, effective, non-superconducting regions
to do this work for us, they had to be of the nanoscale dimensions.
"This is a nice combination of the use of
nanotechnology and superconductivity. With continued advances in nanotechnology,
maybe even more interesting things are possible in the future.
Bob Hawsey, manager of ORNL's superconductivity
program, said the work, sponsored by the Department of Energy's Office of
Electricity Delivery and Energy Reliability, may lead to even more developments
in superconductivity.
"These results demonstrate the potential for the
'second generation' high-temperature superconductors to have broad applicability
in the electric power sector of our economy" Hawsey said. "Our team is working
with three U.S. companies to learn how to apply these innovative, short-sample
laboratory results to industrial processes."
UT-Battelle manages Oak Ridge National Laboratory
for the Department of Energy.
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