But the field from a current line goes in a circle, while the field from a solenoid goes straight. We aren't compensating over a whole room, but we are compensating over several cm. We do it with three pairs of Helmholtz coils--one pair for each axis. You probably wouldn't care about up-down, so you'd only need two pairs of Helmholtz coils.
P=I2R, so adding more wire doesn't require as much energy as raising the current. Also, in my experience, it's harder to find high current power supplies. Doing the calculations, though... it might still be prohibitively expensive.
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P=I2R, so adding more wire doesn't require as much energy as raising the current. Also, in my experience, it's harder to find high current power supplies. Doing the calculations, though... it might still be prohibitively expensive.