In the discharge units, cold plasma is created between two electrodes as the air between them is ionised. In this video, the discharger has a cylindrical outer electrode and a thin, rod-like inner electrode. The unit is seen here from the end, so it appears as an outer ring and an inner point.

With no magnetic field, the plasma discharge (seen here as purple) would form between random points on each electrode. However, when a magnet field is applied, the plasma spreads out into a disc, as seen when the unit is switched off and on in the middle of the video.