Editing Magnetohydrodynamic generator (section)

=== Disc generator ===

[[File:Disk MHD generator.png|thumb|right|upright=1.5|alt=Diagram of a Disk MHD generator|Diagram of a disk MHD generator showing current flows]]
The third and, currently, the most efficient design is the Hall effect disc generator. This design currently holds the efficiency and energy density records for MHD generation. A disc generator has fluid flowing between the center of a disc, and a duct wrapped around the edge. (The ducts are not shown.) The magnetic excitation field is made by a pair of circular [[Helmholtz coils]] above and below the disk. (The coils are not shown.)

The Faraday currents flow in a perfect dead short around the periphery of the disk.

The Hall effect currents flow between ring electrodes near the center duct and ring electrodes near the periphery duct.

The wide flat gas flow reduced the distance, hence the resistance of the moving fluid. This increases efficiency.

Another significant advantage of this design is that the magnets are more efficient. First, they cause simple parallel field lines. Second, because the fluid is processed in a disk, the magnet can be closer to the fluid, and in this geometry, magnetic field strengths increase as the 7th power of distance. Finally, the generator is compact, so the magnet is smaller and uses a much smaller percentage of the generated power.