14 research outputs found
Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors
Quasiclassic Uzadel equations for two-band superconductors in the dirty limit
with the account of both intraband and interband scattering by nonmagnetic
impurities are derived for any anisotropic Fermi surface. From these equations
the Ginzburg-Landau equations, and the critical temperature are obtained.
An equation for the upper critical field, which determines both the temperature
dependence of and the orientational dependence of
as a function of the angle between and the c-axis is
obtained. It is shown that the shape of the curve essentially
depends on the ratio of the intraband electron diffusivities and ,
and can be very different from the standard one-gap dirty limit theory. In
particular, the value can considerably exceed ,
which can have important consequences for applications of . A scaling
relation is proposed which enables one to obtain the angular dependence of
from the equation for at . It is shown
that, depending on the relation between and , the ratio of the upper
critical field for and can both increase and decrease as the temperature decreases. Implications
of the obtained results for are discussed
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Experience in the operation of the International Fusion Superconducting Magnet Test Facility
The International Fusion Superconducting Magnet Test Facility (IFSMTF) was placed under vacuum in October 1985 and cooled in January 1986. It remained at cryogenic temperatures until September 1987, when testing was completed. This paper is an account of the activities of cooling, testing, and maintaining the system during this period. The facility contained six superconducting magnets, arranged in a toroidal array. Each of these D-shaped magnets weighed 40-50 tonnes and was about 5 m by 10 m. The refrigerator system provided atmospheric liquid helium (LHe), about 5000 L in the three pool-boiling coils and the leads, plus a storage capacity of 21,000 L. In addition, the three forced-flow coils were supplied with up to 300 g/s of single-phase helium at 3.8 K and 15 atm. A crew of three or four trained, certified operators handled the cryogenic facility on a 24-h basis for most of the daily activities. Detailed records were maintained, reports of unusual events were prepared and a continuous record of availability was accumulated. At the end of the 22-month period of operation, the cumulative availability was 57%. 1 ref., 13 figs., 2 tabs
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Conductors for tokamak toroidal field coils
This paper describes six conductors which are being developed for use in superconducting toroidal field coils of tokamak fusion machines. Included are three pool boiling and three forced flow concepts. Research and development programs on several of the conductors are under way, jointly involving Oak Ridge National Laboratory (ORNL) and conductor manufacturers. Conductors will be tested in short lengths and in the form of 3m x 2.5m Large Coil Segment (LCS) tests. The conductor development and testing is closely coordinated with the Large Coil Program (LCP) at ORNL
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Test results of the vapor-cooled leads for the IFSMTF
A vapor-cooled lead system that used six pairs of leads in twelve separate dewars was built for the International Fusion Superconducting Magnet Test Facility (IFSMTF). Each of these leads was cooled by helium vapor from a reservoir separate from the coil, in pool boiling or by force flow. Satisfactory acceptance tests were performed on the early production runs of the leads. Inconsistent and anomalously high heat losses were observed on the two pairs of lead assemblies used in the partial-array test. Additional tests on the leads and their associated dewars confirmed satisfactory performance of the lead and dewar and offered an explanation for the excessive losses during the partial-array test
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Integrated composite conductor for the LCS program
The design of a 10 kA 8 T conductor intended for the LCS test program is presented. The interaction of mechanical, thermal, and electrical design requirements are emphasized in the selection of the basic conductor configuration. Evolution of the conductor design from its inception to the final manufactured configuration is traced. Details of the conductor configuration, a steel core about which composite rectangular superconducting elements are cabled, will be given. Using the parameters of this configuration, calculations of electrical loss from a 0.35 T/second and 0.15 T/second pulse are presented. Consideration of possible mechanical motion from the pulsed field is also discussed and analyzed
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Performance of the IFSMTF helium refrigerator in partial-array tests
Performance of the International Fusion Superconducting Magnet Test Facility (IFSMTF) helium refrigerator in Partial Array Tests with three coils is described. The refrigerator was able to cool the coils and facility structure to 4.2 K in 20 days, with maximum temperature differentials of less than 50 K. Boiloff measurements were made for several components; only the lead dewars showed losses substantially higher than expected. Forced-flow cooling tests were also conducted. The coils and facility were warmed back to room temperature in 30 days. Several repairs and improvements were carried out. Results of another recent test on the refrigerator alone are reported
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Startup of Large Coil Test Facility
The Large Coil Test Facility (LCTF) is being used to test superconducting toroidal field coils about one-third the size of those for INTOR. Eventually, six different coils from four countries will be tested. Operations began in 1983 with acceptance testing of the helium refrigerator/liquefier system. Comprehensive shakedown of the facility and tests with the first three coils (from Japan, the United States, and Switzerland) were successfully accomplished in the summer of 1984. Currents up to 10,200 A and fields up to 6.4 T were reached. Data were obtained on performance of refrigerator, helium distribution, power supplies, controls, and data acquisition systems and on the acoustic emission, voltages, currents, and mechanical strains during charging and discharging the coils
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Operating experience of the IFSMTF (International Fusion Superconducting Magnet Test Facility) vapor-cooled lead system
The International Fusion Superconducting Magnet Test Facility (IFSMTF) uses six pairs of vapor-cooled leads (VCLs) to introduce electric power to six test coils. Each VCL is housed in a dewar outside the 11-m vacuum vessel and is connected to the coal via a superconducting bus duct;the various VCLs are rated at 12 to 20 kA. Heat loss through the leads constitutes the single largest source of heat load to the cryogenic system. Concerns about voltage breakdown if a coil quenches have led to precautionary measures such as installation of a N/sub 2/-purged box near the top of the lead and shingles to collect water that condenses on the power buses. A few joints between power buses and VCLs were found to be inadequate during preliminary single-coil tests. This series of tests also pointed to the need for automatic control of helium flow through the leads. This was achieved by using the resistance measurements of the leads to control flow valves automatically. By the time full-array tests were started, a working scheme had developed that required little attention to the leads and that had little impact on the refrigerator between zero and full current to the coils. The operating loss of the VCLs at full current is averaging at about 7.4 gs of warm flow and 360 W of cold-gas return load. These results are compared with predictions that were based on earlier tests. 4 refs., 6 fig