Making Resistive Magnets

Nested Interest

After all the discs are stacked, what's next? If you don't know by now, you really haven't been paying attention.

The four resistive coils of our 45 tesla hybrid magnet. When assembled, they fit inside each other.

More quality control, of course. We connect the magnet to power supply and energize it with 50 amps of current. Each turn in the magnet is tested with a voltmeter, a tool that measures the electrical voltage in a circuit. All the end turns should have the same voltage; all the mid turns should have the same voltage. If the voltmeter picks up low voltage somewhere, the current may be taking an unauthorized shortcut, perhaps due to an overlooked burr.

Finally, it's time to put the coils inside the magnet and hook them up to the electrical source. They are placed one inside the other, like Russian dolls.

The coils run in series: the current spirals down the innermost coil first, then works its way up the next one, passing through the largest coil last, as shown below. The illustration also demonstrates how cold water pumped through the coil keeps the magnet from overheating.

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