Unipolar inductor

A Unipolar inductor usually refers to a device in which a rotating metal disk rotating in a magnetic field, generates an electric current. The metal disk can be any conductor, including a rotating plasma. It is also known as a homopolar generator, unipolar generator, acyclic generator, disk dynamo, or Faraday disk.

Astrophysical unipolar inductors

Unipolar inductors occur in astrophysics where a conductor rotates through a magnetic field, for example, the movement of the highly conductive plasma in a cosmic body’s ionosphere through its magnetic field. In their book, Cosmical Electrodynamics, Hannes Alfvén and Carl-Gunne Fälthammar write:

“Since cosmical clouds of ionized gas are generally magnetized, their motion produces induced electric fields [..] For example the motion of the magnetized interplanetary plasma produces electric fields that are essential for the production of aurora and magnetic storms” [..]

“.. the rotation of a conductor in a magnetic field produces an electric field in the system at rest. This phenomenon is well known from laboratory experiments and is usually called ‘homopolar ‘ or ‘unipolar’ induction. ^[3]

Unipolar inductors have been associated with the aurorae on Uranus,^[4] binary stars,^{[5] [6]} black holes,^{[7] [8]} pulsars (neutron stars),^[2] galaxies,^[9] the Jupiter Io system,^{[10] [11]} the Moon,^{[12] [13]} the Solar Wind,^[14] sunspots,^{[15] [16]} in the Venusian magnetic tail.^[17], the Earth,^[18], and comets.^{[19] [20]}

Notes