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NIST provides key measurements for superconducting magnets for the International Thermonuclear Experimental Reactor.

Superconducting magnets are used in fusion energy projects, such as the International Thermonuclear Experimental Reactor (ITER), to confine and heat the plasma. The superconductors for the ITER's large magnet systems are all "cable-in-conduit conductors" (CICC), which provide both mechanical support for the large magnetic forces and a flow path for the liquid helium required to cool the cable. The superconducting magnet must be operated below the critical current of the cable, which is a function of magnetic field and temperature. Temperature is an important variable, and the local temperature of the conductor depends on the mass-flow rate of the coolant and the distribution of the heat load along the CICC.

Earlier magnet systems that used CICC experienced unexpected degradation of their superconducting properties. To help determine the source of such degradation, NIST scientists measured variable-temperature critical current of a "witness" superconductor strand that was thermally processed along with the superconducting cables used to make the latest two ITER test conductors.

The results of NIST's unique variable-temperature measurements provide a comprehensive mapping of critical current as a function of magnetic field (0 T to 12 T) and temperature (4 K to 17 K), and form a basis for evaluating CICC and magnet performance. NIST scientists used the data to generate curves of electric field versus temperature at constant current and magnetic field. These, in turn, gave a direct indication of the temperature safety margin of the conductor.

NIST's results will be used by Lawrence Livermore National Laboratory, which will test CICC samples at the Plasma Physics Research Center in Villigen, Switzerland, with current up to 100 000 A and magnetic fields up to 12 T, while controlling the mass-flow rate of the coolant.

More information about ITER may be found at www.iter.org.

CONTACT: Ron Goldfarb, (303) 497-3650; goldfarb@boulder.nist.gov.
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Title Annotation:General Developments
Publication:Journal of Research of the National Institute of Standards and Technology
Date:Nov 1, 2003
Words:302
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