Magnetic resonance imaging instruments use very large magnets that consist of many turns of superconducting wire. a typical such magnet has an inductance of 40 h. when the magnet is initially powered up, the current through it must be increased slowly so as not to "quench" the wires out of their superconducting state. one such magnet is specified to have its current increased from 0 a to 150 a over 220 min.

what constant voltage needs to be applied to yield this rate?

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia