Television observations of a barium plasma flux tube extending from near 4500 km to near 10,000 km during a magnetic substorm and dawn sector auroral display indicated several interesting anomalous events. Beyond 5500 km there was a rapid increase in brightness accompanied by flux tube splitting and diffusion, leaving behind a truncated single flux tube. From the orientation of the flux tube compared with theoretical field models the presence of a substantial field-aligned current sheet is deduced. A suggested explanation of these phenomena is given in terms of a plasma potential double layer.