Fig. 10. Evolution of the topology with for the set of parameters given in Fig. 5. For lower values of , the topology is FX and the magnetic configuration is normal. For higher values of the topology is OF and the magnetic configuration is inverse. For a critical value , the topology passes from FX to OF. There, the field is parallel to the inversion line, almost everywhere in the low field region, and the prominence vertical thickness is null. This could be observed as an empty filament channel.