Plasma build-up in stellarators by neutral beams alone

Plasma generation has been achieved in the stellarator W7-AS using neutral beam injection only.Plasma evolution is analysedusing a zero-dimensional model.The model gives guidelines for this method to be successful.Both a low neutral gasstarting pressure and a small fraction of wall recyclingare necessary to get `ignition' by beams.The predictions of the model are compared to experiments on W7-AS and LHD.