a primary potential difference drives an alternating current through the primary coil the primary coil current produces a magnetic field, which changes as the current changes the iron core ...

This magnetic field changes as the current changes ... The induced voltage causes an alternating current to flow. Transformers can only work with alternating current. Input and output voltages ...

How a tokamak works: The electric field induced by a transformer drives a current (big red arrows) through the plasma column. This generates a poloidal magnetic field that bends the plasma current ...