Windings for High Powered Magnets

Physicists, for reasons of their own, like to see what happens to things in high magnetic fields. 'High' means 50 Tesla or more, so the only way to get such fields is the old-fashioned one: dump a huge current through a wire-wound coil, water-cooled if necessary (Figure 32.1). Permanent magnets have a practical field strength limit of 1.5T. Superconducting coils currently are limited to 25T.

The current generates a field-pulse which lasts as long as the current flows. The limits on the field and its duration are set by the material of the coil itself; exceed the limits and the coil either blows itself apart or melts. So choosing the right material for the coil is critical. What should it be? The answer — as we shall show — depends on the pulse duration.

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Pulsed fields are classified according to their duration and strength as shown in Table 32.1. Except for the ultra-short pulses, the fields listed in the table are generated in coils which are expected to survive during the pulse. The design requirements are summarized in Table 32.2.

Table 32.1 Classification of pulsed magnetic fields.

Figure 32.1 Schematic of the high-field magnet.

Table 32.2 The design requirements