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A superconducting magnet is a large inductor and holds a strong magnetic field which carries energy.
Energy must be put into the magnetic field in order to bring it up to strength.
The rate at which energy can be put into a superconducting magnet is limited, because a high rate of energy input can cause heating, which can cause the material to cease ...
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On the experimental side, one experiment that confirms pairs of electrons is flux quantization. The magnetic flux, $\Phi$ through a superconducting ring is quantized in units of: $$\frac{2\pi\hbar c}{q}$$ Experimentally, q is measured to be 2e. See Kittel's discussion of flux quantization.
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