The MHD Hall Generator

At high field-to-conductivity ratios the induced current turns along the flow; the Hall generator collects that axial current instead.

When the current turns

In a strongly magnetized plasma the charge carriers do not move straight along the induced field — they are deflected by the same magnetic field, an effect measured by the Hall parameter (roughly the ratio of gyration to collision frequency). When the Hall parameter is large, the net current develops a substantial component along the flow direction. The Hall generator embraces this: it short-circuits the transverse electrodes and collects the axial current between electrodes at the channel ends.

Trade against the Faraday design

• Faraday: collects transverse current; needs segmented electrodes to beat the Hall short-circuit.
• Hall: collects axial current; a single load, simpler wiring, favored at high Hall parameter.
• Diagonal: electrodes set at an angle to capture a blend — a hybrid used to balance the two.

Why the burner's high field matters here

At 26.49 T plug and 17 T throat fields, the Hall parameter in the conversion channel is naturally large, which pushes the design toward Hall or diagonal configurations rather than a plain continuous-electrode Faraday generator. The ultra-high field that makes MHD conversion powerful also makes the Hall effect strong, so the geometry must be chosen deliberately.

Losses to watch

Hall generators concentrate current at the end electrodes, raising local current density and erosion there. They also depend sensitively on the plasma conductivity, which varies with temperature along the channel. Managing electrode life and conductivity profile is the central engineering task, and it feeds directly into the MHD efficiency-and-losses discussion.