High-Magnetic-Field Research and Facilities [Final Report] (1979) / Chapter Skim
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MAGNET DESIGN AND MATERIALS
MAGNET DESIGN AND MATERIALS
Pages 55-71
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From page 55... ...
Continuous-field generation, for example, progressed from the large iron magnets of the 1920's to 10 T in the 1930's, to 20 T in the early 1960's, and to 30 T in the late 1970's. Each new major increase required significant time and effort to develop technologies, test concepts, and marshal the major new commitment of resources that was needed.
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From page 56... ...
This effort should include a study of high-field superconducting magnets, resistive magnets, and hybrid systems, which combine superconducting outer coils and water-cooled inserts, and which represent the approach most likely to result in the highest steady-state fields, and as such should receive priority attention. Intermediate goals between the available 30 T and the desired 75 T should be pursued; goals of 45 T and 60 T would divide the interval in thirds.
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From page 57... ...
Prior to these developments, continuous fields of this level were available only in those central facilities that had large power supplies.
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From page 58... ...
Although fields of 10 T are easily attained with superconducting magnets, the cost of producing fields substantially above 10 T rises rapidly. Figure 1 gives an approximate cost curve for 5-cm bore coils.
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From page 59... ...
20 30 FIELD (TESLA) FIGURE 2 Limiting winding current density assumed for advanced superconducting coils.
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From page 60... ...
We assume that (a) consideration of coil protection limits overall coil current density to 10 x 103 A/cm2; (b)
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From page 61... ...
Resistive and Hybrid Magnets-Present Status Until the economic arguments in the previous section change, continuous fields much above 20 T will continue to be generated by resistive watercooled magnets or resistive inserts boosted by external superconducting coils. These boosted, or hybrid, systems are a good combination, because they place the resistive elements on the inside where the field is high and the power requirements lowest, and the superconductor on the outside where the field is low enough but the power requirements highest.
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From page 62... ...
Type 30 3.2 10 Hybrid 25 3.2 5 Hybrid 20 3.2 2.5 Hybrid 23.5 3.2 10 Resistive 19.5 5.4 10 Resistive 18.5 3.2 5 Resistive 16 5.4 5 Resistive Table 3 indicates that resistive magnets with power supplies of at least 5.0-MW capacity and hybrid magnets of at least 2.5-MW capacity can produce field magnitudes higher than the 20-T level that is available relatively economically from superconducting magnets. However, there are certain advantages to resistive magnets, even below 20 T, largely as a result of sweep speed.
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From page 63... ...
Higher-field outer superconducting sections will further reduce the power supply required but will also be very expensive. As with the pure superconducting coils discussed in the previous section, a fundamental change in the empirical rule that B x / = constant must occur to allow substantial cost reduction.
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From page 64... ...
QUASI-STATIC PULSE SYSTEMS Present Status Although continuous fields are necessary for many experiments and always desirable, certain experiments can be conducted in shorter times. Pulse times
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From page 65... ...
Precooled magnets that depend on thermal inertia are limited by the product of magnet current density squared times the pulse time (/2r)
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From page 66... ...
The long-pulse magnets, particularly using present fusion program power supplies, represent the least expensive entry into the field range between 30 and 75 T Realization of these ambitious pulse coils will represent a major magnet design challenge for the next few years.
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From page 67... ...
All of these factors usually worsen as the field magnitudes increase. Pulse fields obtained from capacitor discharges have been the principal method of generating fields beyond those available from continuous fields.
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From page 68... ...
shells. The higher the field, the less can be generated by the inner elements where the field is high, and the more must be generated in shells farther out, but at the cost of rapidly increased energy demands.
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From page 69... ...
Many people believe that it will be difficult to greatly exceed 300 T without using flux compression techniques, at least in reasonable volumes and useful time scales. It is perhaps not unreasonable to anticipate useful laboratory-produced fields of more than 500 T with electromagnetic implosion techniques.
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From page 70... ...
Some exploratory work has been done on localized azimuthal megagauss field generation by other techniques. It should be remarked here, however, that the magnetic fields are not uniform but instead vary inversely with distance from the current source.
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From page 71... ...
Some combinations of explosive-driven, transformer-coupled foils and compressing fields produced by large superconducting coils outside the blast shield might produce fields in the 5000-T region. High-field flux compression calculations are uncertain, as they involve not only sophisticated MHD plasma stability considerations but also require equations of state and conductivity information that is poorly known at the extreme conditions encountered.
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